"uuid","repository link","title","author","contributor","publication year","abstract","subject topic","language","publication type","publisher","isbn","issn","patent","patent status","bibliographic note","access restriction","embargo date","faculty","department","research group","programme","project","coordinates"
"uuid:4f63adc9-6cd6-43dc-923e-28a9c4a21cb6","http://resolver.tudelft.nl/uuid:4f63adc9-6cd6-43dc-923e-28a9c4a21cb6","A Comprehensive Study on Measurement Accuracy of Distributed Fiber Optic Sensors Embedded within Capillaries of Solid Structures","Xiao, Y. (TU Delft Structural Integrity & Composites); Rans, C.D. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2023","Embedding fiber optic sensors (FOSs) within parts for strain measurement is attracting widespread interest due to its great potential in the field of structural health monitoring (SHM). This work proposes a novel method of embedding FOSs using capillaries within solid structures and investigates fiber positions and orientation uncertainties within capillaries of different sizes and their influences on strain measurement accuracies. To investigate how the fiber positions and orientation variations influence strain measurement accuracy, both analytical and numerical models are utilized to predict strain distributions along embedded fibers at different positions and with different orientations within the specimen. To verify the predictions, a group of specimens made of Aluminum 6082 was prepared, and the specimens in each group had capillaries of 2 mm, 4 mm, and 6 mm diameters, respectively. Fibers were embedded within each specimen using the capillaries. Four-point bending static tests were conducted for each specimen with embedded FOSs, performing in situ strain measurement. Subsequently, the specimens were partitioned into several pieces, and the cross sections were observed to know the real positions of the embedded fiber. Finally, the strain predictions at the real locations of the fiber were compared with the measured strain from the embedded FOSs. The predicted strain distributions as a function of the fiber positions alone and as a function of both the fiber positions and orientations were compared to assess the influence of fiber orientation change. The results from a combination of analytical, numerical, and experimental techniques suggest that the fiber position from the capillary center is the main factor that can influence strain measurement accuracies of embedded FOSs, and potential fiber misalignments within the capillary had a negligible influence. The fiber position-induced measured error increases from 10.5% to 18.5% as the capillary diameter increases from 2 mm to 6 mm. A 2 mm capillary diameter is able to lead to the lowest measurement error in this study and maintains ease of embedding. In addition, it is found that the measured strain always lies within a strain window defined by the strain distribution along capillary boundaries when there are no cracks. This can be further studied for crack detection.","fiber optic sensor embedding; strain measurement; structural health monitoring; measurement accuracy","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:e0793ab9-18f3-4fd4-83f8-15734ea4eb52","http://resolver.tudelft.nl/uuid:e0793ab9-18f3-4fd4-83f8-15734ea4eb52","Delamination Size Prediction for Compressive Fatigue Loaded Composite Structures Via Ultrasonic Guided Wave Based Structural Health Monitoring","Gul, F.C. (TU Delft Structural Integrity & Composites); Moradi, M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); HADJRIA, RAFIK (Safran Aircraft Engines); LUGOVTSOVA, YEVGENIYA (BAM Federal Institute for Materials Research and Testing); Zarouchas, D. (TU Delft Structural Integrity & Composites)","","2023","Under in-plane compressive load conditions, the growth of a delamination initially induced by an impact can be followed by a fast growth after a threshold level, which leads to a catastrophic failure in composite structures. To avoid reaching this critical level, it is essential to uncover the delamination size and growth pattern in real time. Ultrasonic Guided Waves (UGW) have a strong capability to interrogate and monitor the structure in real-time and thus track the growth of damage, which may occur during the flight cycles. Although various types of damage affect the monitored UGW signals, it is challenging to determine from the UGW signals what types of damage and at what rate of growth are occurring within the structure. UGW signals can be acquired at defined intervals and then analysed to possibly detect different types of damages, such as delamination, and to quantify the rate of damage growth over fatigue cycles. However, correlating the UGW-based Damage Indicators (DIs) with the specific type of damage, such as delamination, and damage growth is a challenging task as the relation between these DIs and the actual damage state is very complex. Therefore, in this study, a supervised Deep Neural Network-based (DNN) prediction model is proposed aiming to diagnose the delamination size of the composite structure by correlating the UGW-based DIs with the quantified time-varying delamination size. UGW data is collected through a network of permanently installed piezoelectric transducers (PZTs). The delamination size is obtained through ultrasonic C-Scan technique at defined cycles. DIs are extracted in time, frequency, and time-frequency domains and used as the input for the DNN-based regression model. Each sensor-actuator path is considered as an independent set of indicators, which are separated for training, validation, and testing purposes. The effect of the different paths on the delamination size prediction is presented along with the model performance on measured delamination growth in woven type composite sample.","Ultrasonic guided waves; Damage Indicators; piezoelectric transducers; PZT; Deep neural network; Structural health monitoring (SHM); Carbon fiber reinforced polymer (CFRP); Compression after impact; Wavelet transform (WT); Signal Processing","en","conference paper","DEStech publications, Inc.","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-06-30","","","Structural Integrity & Composites","","",""
"uuid:86f0e258-98fa-42f8-b779-8aceed685f2b","http://resolver.tudelft.nl/uuid:86f0e258-98fa-42f8-b779-8aceed685f2b","Advanced Health Monitoring of Composite Structures Through Deep Learning-Based Analysis of Lamb Wave Data for Developing Health Indicators","Moradi, M. (TU Delft Structural Integrity & Composites); Gul, F.C. (TU Delft Structural Integrity & Composites); Chiachío, Juan (Universidad de Granada; University of Granada); Benedictus, R. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites)","","2023","A health indicator (HI) serves as an intermediary link between structural health monitoring (SHM) data and prognostic models, and an efficient HI should meet prognostic criteria, i.e., monotonicity, trendability, and prognosability. However, designing a proper HI for composite structures is a challenging task due to the complex damage accumulation process during operational conditions. Additionally, designing a HI that is independent of historical SHM data (i.e., from the healthy state until the current state) is even more challenging as HI and remaining useful life prediction are time-dependent phenomena. A reliable SHM technique is required to extract informative time-independent data, and a powerful model is necessary to construct a proper HI from that data. The lamb wave (LW) technique is a useful SHM method that can extract such time-independent data. However, translating the LW data at each time step to the appropriate HI value
is a challenge. AI—deep learning in this case—offers significant mathematical potential to meet this difficulty. A semi-supervised learning approach is developed to train the model using the simulated ideal HIs as the targets. The model uses the current LW data, without prior or subsequent data, to output the current HI value. Prognostic criteria are then calculated using the entire HI trajectory until the end-of-life. To validate the proposed approach, aging experiments from NASA’s prognostics data repository are used, which include composite specimens subjected to a tension-tension fatigue loading and monitored using the LW technique. The LW data is first processed using the Hilbert transform, and then, upper and lower signal envelopes in two states – baseline and current time – are used to feed the deep learning model. The results confirm the effectiveness of the proposed approach according to the prognostic criteria. The effect of different triggering frequencies of the LW system on the results is also discussed in terms of the prognostic criteria.","Prognostics and health management (PHM); Intelligent health indicator; Semi-supervised learning; Tension-Tension fatigue; Composite structures; Signal Processing; machine learning (ML) algorithms; Deep learning (DL); Structural health monitoring (SHM); Guided waves","en","conference paper","DEStech publications, Inc.","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-06-30","","","Structural Integrity & Composites","","",""
"uuid:ac148328-5b6f-495c-a862-cc16bd0610ce","http://resolver.tudelft.nl/uuid:ac148328-5b6f-495c-a862-cc16bd0610ce","Intelligent health indicator construction for prognostics of composite structures utilizing a semi-supervised deep neural network and SHM data","Moradi, M. (TU Delft Structural Integrity & Composites); Broer, Agnes A.R. (TU Delft Structural Integrity & Composites); Chiachío, Juan (University of Granada); Benedictus, R. (TU Delft Structural Integrity & Composites); Loutas, Theodoros H. (University of Patras); Zarouchas, D. (TU Delft Structural Integrity & Composites)","","2023","A health indicator (HI) is a valuable index demonstrating the health level of an engineering system or structure, which is a direct intermediate connection between raw signals collected by structural health monitoring (SHM) methods and prognostic models for remaining useful life estimation. An appropriate HI should conform to prognostic criteria, i.e., monotonicity, trendability, and prognosability, that are commonly utilized to measure the HI's quality. However, constructing such a HI is challenging, particularly for composite structures due to their vulnerability to complex damage scenarios. Data-driven models and deep learning are powerful mathematical tools that can be employed to achieve this purpose. Yet the availability of a large dataset with labels plays a crucial role in these fields, and the data collected by SHM methods can only be labeled after the structure fails. In this respect, semi-supervised learning can incorporate unlabeled data monitored from structures that have not yet failed. In the present work, a semi-supervised deep neural network is proposed to construct HI by SHM data fusion. For the first time, the prognostic criteria are used as targets of the network rather than employing them only as a measurement tool of HI's quality. In this regard, the acoustic emission method was used to monitor composite panels during fatigue loading, and extracted features were used to construct an intelligent HI. Finally, the proposed roadmap is evaluated by the holdout method, which shows a 77.3% improvement in the HI's quality, and the leave-one-out cross-validation method, which indicates the generalized model has at least an 81.77% score on the prognostic criteria. This study demonstrates that even when the true HI labels are unknown but the qualified HI pattern (according to the prognostic criteria) can be recognized, a model can still be built that provides HIs aligning with the desired degradation behavior.","Composite structures; Intelligent health indicator; Prognostic and health management; Semi-supervised deep neural network; Structural health monitoring","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:cd05702e-a4ec-437b-981c-cd69042679a3","http://resolver.tudelft.nl/uuid:cd05702e-a4ec-437b-981c-cd69042679a3","Investigation on the effect of interface properties on compressive failure behavior of 3D woven composites through micromechanics-based multiscale damage model","Zheng, T. (TU Delft Structural Integrity & Composites; Harbin Institute of Technology); Guo, Licheng (Harbin Institute of Technology); Sun, Ruijian (Beijing Institute of Astronautical Systems Engineering, Beijing); Wang, Tongtong (Harbin Institute of Technology); Hong, Changqing (Harbin Institute of Technology); Benedictus, R. (TU Delft Structural Integrity & Composites); Pascoe, J.A. (TU Delft Structural Integrity & Composites)","","2023","In this paper, the effect of interface properties on the compressive failure behavior of 3D woven composites (3DWC) is investigated by incorporating a micromechanics-based multiscale damage model (MMDM). The correlation between the mesoscopic stress of yarns and microscopic stress of constituents is established by defining a stress amplification factor. With the microscopic stresses, the fiber breakage and matrix failure can be separately evaluated at the microscale, without assuming the yarns as transversely isotropic homogeneous materials. Especially, the interfacial debonding between yarns and matrix is also a dominant damage mode within 3DWC. Given that there is still a lack of studies on the influence of interfacial properties on the compressive failure behavior of 3DWC, it is meaningful to perform numerical parametric studies to reveal how the interface properties contribute to the damage mechanisms of 3DWC under compressions. The predicted results indicate that with the increase of interface strengths and fracture toughness, the compressive resistance of 3DWC can be significantly improved, resulting in higher strength and failure strain. Additionally, the studied 3DWCs with weak, medium and strong interfaces exhibit different damage development processes.","3D woven composites; Compressive failure behavior; Interface; Micromechanics-based multiscale damage model; Numerical parametric study","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-11-29","","","Structural Integrity & Composites","","",""
"uuid:f17718be-e3cf-4bd0-aa1b-4ad057e06906","http://resolver.tudelft.nl/uuid:f17718be-e3cf-4bd0-aa1b-4ad057e06906","Analysis of Stochastic Matrix Crack Evolution in CFRP Cross-Ply Laminates under Fatigue Loading","Li, X. (TU Delft Structural Integrity & Composites; Center of Excellence in Artificial Intelligence for Structures); Benedictus, R. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites; Center of Excellence in Artificial Intelligence for Structures)","","2023","The present work aims at understanding the stochastic matrix crack evolution in CFRP cross-ply laminates under tension–tension fatigue loading. An experimental campaign was carried out on twenty-three specimens at different stress levels, while two optical techniques were used for the in-situ monitoring of the accumulation of transverse matrix cracks. The results showed a significant scatter in crack evolution among specimens. This stochastic behaviour was further investigated using image analysis and numerical modelling. It was found that transverse matrix cracks can be classified into the independent and dependent cracks based on a critical crack spacing. Furthermore, the severity of interaction among cracks was quantified by introducing a dependent crack ratio. Finally, a strength-based probabilistic model was proposed to describe the scattering regime of the crack evolution. The agreement between model and test results indicates that local strength variations of 90 plies are the dominant scattering source governing the initial fatigue resistance to cracking and determining the accumulation of transverse matrix cracks among specimens. These results may provide a new insight into the stochastic nature of matrix cracking in composite laminates and aid in the design of fatigue resistance properties.","Composite laminates; Fatigue; In-situ damage monitoring; Phenomenological model","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:a83f0089-d274-447c-bbed-9cafabe3eb5c","http://resolver.tudelft.nl/uuid:a83f0089-d274-447c-bbed-9cafabe3eb5c","Intelligent Health Indicators Based on Semi-supervised Learning Utilizing Acoustic Emission Data","Moradi, M. (TU Delft Structural Integrity & Composites); Broer, Agnes A.R. (TU Delft Structural Integrity & Composites); Chiachío, Juan (Universidad de Granada); Benedictus, R. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites)","Rizzo, Piervincenzo (editor); Milazzo, Alberto (editor)","2023","Health indicators are indices that act as intermediary links between raw SHM data and prognostic models. An efficient HI should satisfy prognostic requirements such as monotonicity, trendability, and prognosability in such a way that it can be effectively used as an input in a prognostic model for remaining useful life estimation. However, discovering or designing a suitable HI for composite structures is a challenging task due to the inherent complexity of the evolution of damage events in such materials. Previous research has shown that data-driven models are efficient for accomplishing this goal. Large labeled datasets, however, are normally required, and the SHM data can only be labeled, respecting prognostic requirements, after a series of nominally identical structures are tested to failure. In this paper, a semi-supervised learning approach based on implicitly imposing prognostic criteria is adopted to design a novel HI suitable. To this end, single-stiffener composite panels were subjected to compression-compression fatigue loading and monitored using acoustic emission (AE). The AE data after signal processing and feature extraction were fused using a multi-layer LSTM neural network with criteria-based hypothetical targets to generate an intelligent HI. The results confirm the performance of the proposed scenario according to the prognostic criteria.","Composite structures; Intelligent health indicator; Prognostic and health management; Semi-supervised deep neural network; Structural health monitoring","en","conference paper","Springer","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-10-16","","","Structural Integrity & Composites","","",""
"uuid:ef65aeeb-0372-41d7-89b7-89771a72708f","http://resolver.tudelft.nl/uuid:ef65aeeb-0372-41d7-89b7-89771a72708f","Hierarchical Upscaling of Data-Driven Damage Diagnostics for Stiffened Composite Aircraft Structures","Broer, Agnes A.R. (TU Delft Structural Integrity & Composites); Yue, N. (TU Delft Structural Integrity & Composites); Galanopoulos, Georgios (University of Patras); Benedictus, R. (TU Delft Structural Integrity & Composites); Loutas, Theodoros (University of Patras); Zarouchas, D. (TU Delft Structural Integrity & Composites)","Rizzo, Piervincenzo (editor); Milazzo, Alberto (editor)","2023","To move towards a condition-based maintenance practice for aircraft structures, design of reliable health management methodologies is required. Development of diagnostic methodologies is commonly realised on simplified sample structures with assumptions that methodologies can be adapted for application to realistic aircraft structures under in-service conditions. Yet such actual applications are not conducted. In this work, we study the development of diagnostic methodologies to training structures and their application to dissimilar testing structures. A heterogeneous population is considered, consisting of single-stiffener composite panels for methodology development and training and a multi-stiffener composite panel for application and testing. Characteristics as its composite material, lay-up, and temperature condition are constant while topologies and applied loads differ between the dissimilar structures. Damage in the structural panels is monitored on multiple diagnostic levels using a variety of structural health monitoring (SHM) techniques, including acoustic emission and distributed strain sensing. Specifically, we develop diagnostic methods for localising and monitoring disbond growth after impact using strain data collected during fatigue testing of multiple single-stiffener panels and apply these for disbond monitoring in an upscaled version of a multi-stiffener panel. In this manner, this study aids in the maturement and application of SHM methodologies to realistic aircraft structures.","Aircraft; Composite structures; Damage diagnostics; Population; Upscaling","en","conference paper","Springer","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-01-01","","","Structural Integrity & Composites","","",""
"uuid:19ccdf3f-2f9c-436b-b9a1-d432687e80f5","http://resolver.tudelft.nl/uuid:19ccdf3f-2f9c-436b-b9a1-d432687e80f5","Improving the quality of continuous ultrasonically welded thermoplastic composite joints by adding a consolidator to the welding setup","Jongbloed, B.C.P. (TU Delft Aerospace Structures & Computational Mechanics); Vinod, R. (Student TU Delft); Teuwen, Julie J.E. (TU Delft Aerospace Manufacturing Technologies); Benedictus, R. (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Aerospace Structures & Computational Mechanics)","","2022","Continuous ultrasonic welding is a promising high-speed and energy-efficient joining technique for thermoplastic composite structures. However, in the current state-of-the-art research on the topic numerous deconsolidation voids could be identified at the welding interface, which results in a strength knock-down. The aim of this study is, therefore, to improve the quality of continuous ultrasonically welded joints by adding a consolidation shoe to the welding setup. To determine the required consolidation pressure, the size of the shoe, and its distance from the sonotrode a stepwise approach was followed based on the static ultrasonic welding process. The closest consolidation distance, best representing the static welding conditions, did not improve the weld quality as significant porosity was still found in the weld line and in the adherends. However, for the furthest consolidation distance high-quality continuous welds were obtained with almost no porosity and a high strength.","Fusion bonding; Ultrasonic welding; Consolidation; Joining; CF/PPS; PPS; CF","en","journal article","","","","","","","","","","","Aerospace Structures & Computational Mechanics","","",""
"uuid:f8ed199b-dab5-4684-a08b-085a4b5e13ac","http://resolver.tudelft.nl/uuid:f8ed199b-dab5-4684-a08b-085a4b5e13ac","The Need for Multi-Sensor Data Fusion in Structural Health Monitoring of Composite Aircraft Structures","Broer, Agnes A.R. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites)","","2022","With the increased use of composites in aircraft, many new successful contributions to the advancement of the structural health monitoring (SHM) field for composite aerospace structures have been achieved. Yet its application is still not often seen in operational conditions in the aircraft industry, mostly due to a gap between research focus and application, which constraints the shift towards improved aircraft maintenance strategies such as condition-based maintenance (CBM). In this work, we identify and highlight two key facets involved in the maturing of the SHM field for composite aircraft structures: (1) the aircraft maintenance engineer who requires a holistic damage assessment for the aircraft’s structural health management, and (2) the upscaling of the SHM application to realistic composite aircraft structures under in-service conditions. Multi-sensor data fusion concepts can aid in addressing these aspects and we formulate its benefits, opportunities, and challenges. Additionally, for demonstration purposes, we show a conceptual design study for a fusion-based SHM system for multi-level damage monitoring of a representative composite aircraft wing structure. In this manner, we present how multi-sensor data fusion concepts can be of benefit to the community in advancing the field of SHM for composite aircraft structures towards an operational CBM application in the aircraft industry.","aircraft components; composite structures; condition-based maintenance; data fusion; health management; structural health monitoring","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:87b86bc3-9a74-4deb-9c59-37e0c82dca9f","http://resolver.tudelft.nl/uuid:87b86bc3-9a74-4deb-9c59-37e0c82dca9f","On the Challenges of Upscaling Damage Monitoring Methodologies for Stiffened Composite Aircraft Panels","Broer, Agnes A.R. (TU Delft Structural Integrity & Composites); Yue, N. (TU Delft Structural Integrity & Composites); Galanopoulos, Georgios (University of Patras); Benedictus, R. (TU Delft Structural Integrity & Composites); Loutas, Theodoros (University of Patras); Zarouchas, D. (TU Delft Structural Integrity & Composites)","Farhangdoust, Saman (editor); Guemes, Alfredo (editor); Chang, Fu-Kuo (editor)","2022","Health management methodologies for condition-based maintenance are often developed using sensor data collected during experimental tests. Most tests performed in laboratories focus on a coupon level or flat panels, while structural component testing is less commonly seen. As researchers, we often consider our experimental tests to be representative of a structure in a final application and consider the developed methodologies to be transferrable to these real-life structures. Yet, structures in their final applications such as wind turbines or aircraft are often larger, more complex, might contain various assembly details, and are loaded in complex conditions. These factors might influence the performance of developed diagnostic and prognostic methodologies and should therefore not be ignored.
In our work, we consider the aspects of upscaling structural health monitoring (SHM) methodologies for stiffened composite panels with the design of the panels inspired by an aircraft wing structure. For this, we examine two levels of panels, namely a single- and multi-stiffener composite panel, where we consider the single-stiffener panel to be a representative lower-level version of the multi-stiffener panel. Multiple SHM sensors (acoustic emission, Lamb waves, strain sensing) were installed on both composite panels to monitor damage propagation during testing. We identify and analyse challenges and further discuss considerations that must be taken during upscaling of diagnostics and prognostics, and with that, aid in the development of health management methodologies for condition-based maintenance.","","en","conference paper","DEStech Publications Inc.","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","","","","Structural Integrity & Composites","","",""
"uuid:01955ba2-a841-49e8-bb5d-a6c9c5262514","http://resolver.tudelft.nl/uuid:01955ba2-a841-49e8-bb5d-a6c9c5262514","The Faculty of Aerospace Engineering at Delft University of Technology","De Breuker, R. (TU Delft Aerospace Structures & Computational Mechanics); Benedictus, R. (TU Delft Structural Integrity & Composites); Bisagni, C. (TU Delft Aerospace Structures & Computational Mechanics); Boneschansker, I. (TU Delft Communication LR); Melkert, J.A. (TU Delft Flight Performance and Propulsion); Snellen, M. (TU Delft Control & Operations; TU Delft Aircraft Noise and Climate Effects); Veldhuis, L.L.M. (TU Delft Flow Physics and Technology; TU Delft Flight Performance and Propulsion); Verdegaal, F.M. (TU Delft Support Aerospace Engineering); Visser, P.N.A.M. (TU Delft Space Engineering; TU Delft Space Systems Egineering); Werij, H.G.C. (TU Delft Aerospace Engineering)","","2022","The Faculty of Aerospace Engineering is one of eight faculties at Delft University of Technology. It is one of the most comprehensive academic and innovation communities worldwide focusing on aerospace engineering. Its 120 professors and 70 researchers are mentoring and teaching around 2,800 BSc/MSc students and more than 350 PhD candidates while working in all aerospace disciplines. It’s a powerhouse in aerospace education, research, and innovation, within the top 10 in the world. Our priority themes? Sustainable aerospace, digital transformation, including Artificial Intelligence, bio-inspired engineering and smart instruments and systems. Here’s our story.","TU Delft; aerospace","en","journal article","","","","","","","","","Aerospace Engineering","Control & Operations","Aerospace Structures & Computational Mechanics","","",""
"uuid:c956b7ae-daa8-49c4-bd1f-9f6e5a73481c","http://resolver.tudelft.nl/uuid:c956b7ae-daa8-49c4-bd1f-9f6e5a73481c","Spectral characteristics of gold nanoparticle doped optical fibre under axial strain","Wang, X. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites)","","2022","Nanoparticle (NP) doping of optical fibres can be used to increase the intensity of the backscattered light used for distributed strain sensing and has shown the advantages of high precision strain detection and multiplex sensing experimentally. However, the backscatter spectral characteristics of NP-doped optical fibres have not been described even though they are quite different from the spectra from fibre Bragg gratings (FBGs) or commercial single mode fibres. In this paper, gold NPs, used as the contrast agent in the optical fibre to increase the intensity of the backscattered light, were investigated from the aspect of their spectra. A single scattering model with Mie theory and an effective refractive index (RI) model were used to evaluate the backscattered light spectra and the Monte Carlo Method was used for seeding NPs. The results showed that the strain responsivity of gold-NP doped fibres with low volume ratio doping (single scattering restriction) are close to FBGs and commercial fibres. High volume ratios of gold NP doping increase the imaginary part of the RI of the optical fibre, which has a significant influence on the spectra in the wavenumber domain. These theoretical insights may promote the future engineering design of NP-doped fibre sensors.","","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:1ed8cfcc-aa12-4ea1-b148-d3d1b90114fe","http://resolver.tudelft.nl/uuid:1ed8cfcc-aa12-4ea1-b148-d3d1b90114fe","How literature reviews influence the selection of fatigue analysis framework","Bhangale, J.A. (TU Delft Structural Integrity & Composites); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Bersee, H.E.N. (TU Delft Structural Integrity & Composites; Suzlon Energy Limited)","Vassilopoulos, Anastasios P. (editor); Michaud, Véronique (editor)","2022","Prediction models for fatigue in engineering applications are developed within a fatigue analysis framework, deliberately selected in some cases, but mostly chosen without substantiation. The proposition of this paper is that selecting the most appropriate framework can only be done with the knowledge and a complete overview of existing frameworks and their systematic categorization. In particular for composite materials, where due to coexistence of different mechanisms and their complex interaction under fatigue loading, only a unified approach can characterize the complete fatigue phenomenon. To that aid, this paper provides a complete overview of existing fatigue analysis frameworks for various materials along with such systematic categorization. Each analysis framework is based on a specific methodology that evolved over time. Hence, this overview is provided following the time stamp evolution of each methodology within different analysis frameworks. With such an overview, one can conclude that for fatigue analysis of composite materials, the theory of the thermodynamics of the irreversible processes and continuum damage mechanics framework provides the required unified approach. Additionally, this paper demonstrates that many material classes, like metals and composites, can be analysed using a common framework. This common framework has similarity up to a certain level, and at the detailed level, it differs by addressing the difference in material class-specific mechanisms.","Wind turbine blades; leading edge protection; droplet impact computational modelling; multilayer systems","en","conference paper","EPFL Lausanne, Composite Construction Laboratory","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:a5bf48ea-6c08-46f6-abc8-4c8a02805431","http://resolver.tudelft.nl/uuid:a5bf48ea-6c08-46f6-abc8-4c8a02805431","Progressive Damage Accumulation Process of CFRP Cross-Ply Laminates during the Early Fatigue Life","Li, X. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites)","Vassilopoulos, Anastasios P. (editor); Michaud, Véronique (editor)","2022","The present work aims at investigating the progressive damage accumulation process of CFRP laminates in an interactive scheme, with a special focus on the early fatigue life where mainly matrix-dominant damage accumulates and stiffness degrades significantly. An in-situ damage monitoring system, containing edge observation, digital image correlation and acoustic emission techniques, was established to characterize and quantify the accumulation of transverse cracks and delamination. Two cross-ply configurations ([0/902]s and [02/904]s) and different stress levels were involved in the experimental campaign. Dependent crack ratio was proposed to reflect the interaction among transverse cracks, and saturated crack density was used to represent the interactive level between transverse cracks and delamination. Results showed that generation of transverse cracks and their interaction govern the early fatigue damage accumulation of the [0/902]s laminates, while not only the interaction among cracks but also the interaction between both damage mechanisms were observed for the [02/904]s laminates.","Delamination; Fatigue damage; Stiffness degradation; Transverse crack","en","conference paper","EPFL Lausanne, Composite Construction Laboratory","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:6914a423-0f68-4a11-89af-00795ba2a081","http://resolver.tudelft.nl/uuid:6914a423-0f68-4a11-89af-00795ba2a081","The effect of pick-up point location on fibre angle devation in Non-Crimp Fabrics","de Zeeuw, C.M. (TU Delft Delft Aerospace Structures and Materials Laboratory); Peeters, D.M.J. (TU Delft Aerospace Structures & Computational Mechanics); Bergsma, O.K. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","Vassilopoulos, Anastasios P. (editor); Michaud, Véronique (editor)","2022","For pick-and-place processes to become widely implemented in industry a consistent and acceptable product quality needs to be achieved. One important quality criterion is the fiber angle deviations in the reinforcement. Handling a reinforcement will subject it to forces due to e.g. gravity and accelerations. These forces can result in in-plane shear and subsequently in fiber angle deviations. The current work looks at predicting and preventing in-plane shear induced fiber angle deviations by studying the positioning of pick-up points. In the state of the art the positioning of individual pick-up points is typically either not discussed or is based on the mould where the fabric is to be draped on – not on the effect of the handling on the fabric. The relationship between the positioning of the pick-up points and the behavior of the fabric should however also be considered. Finite element simulations validated through experimental work will be used to study the influence of pick-up point location on the in-plane shear strain for a bi-axial Non Crimp Fabric [NCF]. In [1] tolerances have been set for the fiber angle deviations, additionally the relationship between in-plane shear strain and fiber angle deviations has been demonstrated for the specific NCF. These results are used in the present work to evaluate the results from the simulations. The current work will demonstrate that it is possible to control the in-plane shear induced fiber angle deviations by varying the position and number of the pick-up points. Additionally, It will show whether simulations for the positioning of pick-up points on large reinforcements can be simplified by looking at one instance of a repeating pattern. The paper will provide a framework for the determination of positioning of pick-up points while predicting and preventing in-plane shear induced fiber angle deviations.","Pick-and-place; automation; fabrics/textiles; non-crimp fabrics","en","conference paper","EPFL Lausanne, Composite Construction Laboratory","","","","","","","","","","Delft Aerospace Structures and Materials Laboratory","","",""
"uuid:78b96ff4-9a16-4cce-aba4-a0a150373b90","http://resolver.tudelft.nl/uuid:78b96ff4-9a16-4cce-aba4-a0a150373b90","Interpretable neural network with limited weights for constructing simple and explainable HI using SHM data","Moradi, M. (TU Delft Structural Integrity & Composites); Komninos, P. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites)","Kulkarni, Chetan (editor); Saxena, Abhinav (editor)","2022","Recently, companies all over the world have been focusing on the improvement of autonomous health management systems in order to enhance performance and reduce downtime costs. To achieve this, the remaining useful life predictions have been given remarkable attention. These predictions depend on the proper designing process and the quality of health indicators (HI) generated from structural health monitoring sensors based on prior established multiple prognostic evaluation criteria. Constructing such HIs from noisy sensory data demands powerful models that enable the automatic selection and fusion of features taken from those relevant measurements. Deep learning models are promising to autonomously extract features in scenarios with a huge volume of data without requiring considerable domain expertise. Nonetheless, the features established by artificial neural networks are complicated to comprehend and cannot be regarded as physical system characteristics. In this regard, the goal of this paper is to extend a new model; an interpretable artificial neural network that enables the automatic selection and fusion of features to construct the most appropriate HIs with remarkably fewer parameters. This model consists of additive and multiplicative layers that provide a feature fusion that better reflects the system’s physical properties. Additionally, the weights are discretized in two ways: a) using a ternary form with values {-1, 0, 1}, and b) relaxing the aforementioned ternary form by rounding the weights at the first decimal point in the range of [-1, 1]. Both discretization techniques have the ability to softly control the number of parameters that should be ignored. This trick guarantees interpretability for the neural network by extracting simple yet powerful equations representing the constructed HIs. Finally, the model’s performance is evaluated and compared with other approaches using a practical case study. The results show that the proposed approach's designed HIs are both interpretable and of high quality according to the criteria of the HI's evaluation.","Prognostics and Health Management (PHM); Structural Health Monitoring (SHM); Intelligent health indicator; Interpretable neural network; C-MAPSS turbofan engines; Machine learning; Artificial Intelligent (AI)","en","conference paper","PHM Society","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:d0de85b2-ca3b-4292-ae5a-c0f0c8c80719","http://resolver.tudelft.nl/uuid:d0de85b2-ca3b-4292-ae5a-c0f0c8c80719","Micromechanics-based multiscale progressive failure simulation of 3D woven composites under compressive loading with minimal material parameters","Zheng, T. (TU Delft Structural Integrity & Composites; Harbin Institute of Technology); Guo, Licheng (Harbin Institute of Technology); Benedictus, R. (TU Delft Structural Integrity & Composites); Pascoe, J.A. (TU Delft Structural Integrity & Composites)","","2022","A novel micromechanics-based multiscale progressive damage model, employing minimal material parameters, is proposed in this paper to simulate the compressive failure behaviours of 3D woven composites (3DWC). The highly realistic constructions of microscopic and mesoscopic representative volume cells are accomplished, and a set of strain amplification factor is employed to bridge the meso-scale and micro-scale numerical calculations. Considering that the multiple failure mechanisms of 3DWC under compression are all caused by the matrix failure from the microscopic perspective, a new method incorporating the micromechanics of failure (MMF) theory and 3D kinking model is developed to identify the micro matrix failure associated with the kinking of yarns, inter-fiber fracture and pure matrix failure. As a result, only the matrix parameters are required for the failure simulation of 3DWC, eliminating the necessity of using other material parameters such as the fracture toughness and failure strengths of fiber yarns, which are generally difficult to accurately obtain through experiments. The newly proposed damage model is numerically integrated into ABAQUS with a user-defined subroutine UMAT. The numerical predictions and the experimental results exhibit good agreement, verifying the feasibility and accuracy of the novel damage model.","A. Polymer-matrix composites (PMCs); A. Textile composites; B. Non-linear behaviour; C. Multiscale modeling; C. Representative volume element (RVE)","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","","Structural Integrity & Composites","","",""
"uuid:be45a8b2-97a2-4b1c-a88a-ed7d82a61d32","http://resolver.tudelft.nl/uuid:be45a8b2-97a2-4b1c-a88a-ed7d82a61d32","Assessment of the Measurement Performance of the Multimodal Fibre Optic Shape Sensing Configuration for a Morphing Wing Section","Nazeer, N. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2022","In this paper, with the final aim of shape sensing for a morphing aircraft wing section, a developed multimodal shape sensing system is analysed. We utilise the method of interrogating a morphing wing section based on the principles of both hybrid interferometry and Fibre Bragg Grating (FBG) spectral sensing described in our previous work. The focus of this work is to assess the measurement performance and analyse the errors in the shape sensing system. This includes an estimation of the bending and torsional deformations of an aluminium mock-up section due to static loading that imitates the behaviour of a morphing wing trailing edge. The analysis involves using a detailed calibration procedure and a multimodal sensing algorithm to measure the deflection and shape. The method described In this paper, uses a standard single core optical fibre and two grating pairs on both the top and bottom surfaces of the morphing section. A study on the fibre placement and recommendations for efficient monitoring is also included. The analysis yielded a maximum deflection sensing error of 0.7 mm for a 347 × 350 mm wing section.","Experimental mechanics; Fibre Bragg Grating; Morphing wing; Multimodal sensing; Optical fibre sensing; Optical interferometry; Shape sensing; Spectral sensing; Strain measurement; Structural health monitoring","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:4969970c-998a-4a38-aa7f-7aa4d0291231","http://resolver.tudelft.nl/uuid:4969970c-998a-4a38-aa7f-7aa4d0291231","Early fatigue damage accumulation of CFRP Cross-Ply laminates considering size and stress level effects","Li, X. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites)","","2022","Ply-block size and stress level effect on accumulation of transverse cracks and delamination are investigated during early fatigue life of CFRP laminates. Tension-tension fatigue tests under different stress levels were performed for two cross-ply configurations. Edge observation with digital cameras, digital image correlation and acoustic emission were employed for in-situ damage monitoring. Transverse cracks were dominant for [0/902]s laminates with almost non-existent delamination, while different interactive levels between both damage mechanisms occurred for [02/904]s laminates. Poisson's ratio identifies whether early fatigue damage is dominant by transverse cracks or involves delamination. Cumulative AE energy is a helpful indicator of crack density.","Acoustic emission; Delamination; Poisson's ratio; Stiffness degradation; Transverse cracking","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:8c131585-c91e-4407-ad3e-329f1e05546c","http://resolver.tudelft.nl/uuid:8c131585-c91e-4407-ad3e-329f1e05546c","Plasmon resonance based gold nanoparticle doped optical fibre strain sensing","Wang, X. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites)","","2022","Strain-based structural health monitoring (SHM) relies on high performance strain sensing methods. Gold nanoparticle (NP) doped fibre optic sensors not only have the potential to increase the intensity of the backscattered signal to increase the signal to noise ratio but also have plasmon resonance peaks in the visible light range. The spectral peak shift of the plasmon resonance may be used for strain sensing. In this paper, the spectral peak shift of the plasmon resonance of an optical fibre containing gold NPs under axial strain was analysed. A modified Lorentz-Drude (LD) model with the T-matrix method was used and the spectral peak shifts of spheroidal NPs under strain were calculated. An approximate analytical expression was derived for faster calculation. The modelling presented in this paper shows that the ratio of the change of the peak wavelength to the strain can be related to the refractive index (RI) change of the optical fibre under strain, the shape change of the gold NP, and the RI change of the gold NP. The peak shift was also observed experimentally in an optical adhesive containing gold NPs under compression. The peak shifts were analysed at different RI of the optical fibres, 1.35, 1.45, 1.55 and 1.65 respectively, in order to cover the range of RI of fused silica and some polymer materials. The results confirm experimentally that the applied axial strain can induce the peak wavelength shift by the NPs. By choosing a different optical fibre or the properties of the NPs, the wavelength change ratio has the potential to be tuned, which may be used for highly sensitive strain sensing.","Gold nanoparticle; Optical fibre; Plasmon resonance; Strain sensing","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:1f8154f7-28f7-46fd-922f-814e25c4a2a1","http://resolver.tudelft.nl/uuid:1f8154f7-28f7-46fd-922f-814e25c4a2a1","A reliable progressive fatigue damage model for life prediction of composite laminates incorporating an adaptive cyclic jump algorithm","Zheng, T. (TU Delft Structural Integrity & Composites; Harbin Institute of Technology); Guo, Licheng (Harbin Institute of Technology); Wang, Zhenxin (AECC Commercial Aircraft Engine Co., Ltd); Benedictus, R. (TU Delft Structural Integrity & Composites); Pascoe, J.A. (TU Delft Structural Integrity & Composites)","","2022","In this paper, a reliable progressive fatigue damage model (PFDM) for predicting the fatigue life of composite laminates is proposed by combining the normalized fatigue life model, nonlinear residual degradation models and fatigue-improved Puck criterion. To balance the accuracy of life predictions and computational efficiency, an adaptive cyclic jump algorithm is developed and implemented within the PFDM. The sensitivity of life prediction to cyclic jump parameter has been greatly reduced by correlating the cyclic jump with the increment time and viscous coefficient. Therefore, the cyclic jump parameter can be arbitrarily selected within a relatively large range to obtain convergent results. When incorporating the adaptive cyclic jump algorithm, there is no need to define a standard for determining the material failure in numerical calculations, which effectively eliminates an artificially induced uncertainty in life predictions. Two sets of experiments are conducted to validate the proposed PFDM. The numerical predictions including static failure strength and fatigue life correlate reasonably well with the available experimental data.","A. Laminate; A. polymer-matrix composites (PMCs); B. Fatigue; C. Finite element analysis (FEA); D. Life prediction","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","","Structural Integrity & Composites","","",""
"uuid:f2642a6d-a647-4232-8d9c-45cedfc75cec","http://resolver.tudelft.nl/uuid:f2642a6d-a647-4232-8d9c-45cedfc75cec","Setting bounds for in-plane shear induced fiber angle deviations in bi-axial non-crimp fabrics","de Zeeuw, C.M. (TU Delft Delft Aerospace Structures and Materials Laboratory; SAM|XL); Peeters, D.M.J. (TU Delft Aerospace Structures & Computational Mechanics); Bergsma, O.K. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites; SAM|XL)","","2022","For pick-and-place processes to become widely implemented in industry a consistent and acceptable product quality needs to be achieved. In the state of the art it is assumed that reinforcements will be in perfect condition at the start of forming or draping. In reality the handling process can already result in undesired deformations. The current work will look at fiber angle deviations that occur during this process due to in-plane shear. It is shown that bounds can be set for these fiber angle deviations based on experimental work. Periodic representative volume element homogenization is used to obtain homogenized material properties for a bi-axial non-crimp fabric with a specific construction. With these material properties the in-plane shear strain, and thus the fiber angle deviations, can be predicted. The presented methodology and results obtained using it can be a basis in the design process for automated handling of reinforcements and for in-situ quality control of the pick-and-place process.","composite fabrics; composites; high performance fabrics; performance; structure properties; technical nonwoven fabrics","en","journal article","","","","","","","","","","","Delft Aerospace Structures and Materials Laboratory","","",""
"uuid:3992c564-6b6c-478e-b566-5c6d5362c9e2","http://resolver.tudelft.nl/uuid:3992c564-6b6c-478e-b566-5c6d5362c9e2","Plasmon resonance spectral peak shift due to morphing of gold nanoparticles for strain sensing","Wang, X. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites)","Berghmans, Francis (editor); Zergioti, Ioanna (editor)","2022","The plasmon resonance spectral peak of a gold spherical nanoparticle (NP) will shift when the NP shape is changed from sphere to spheroid. This may be used as a novel strain detection method with gold NPs embedded in a medium of different refractive index (RI). Applying a strain to the external medium will cause a change in the shape of the NP from spherical to spheroidal. In our previous work, it was found that when the RI change of the medium surrounding the NPs is close to zero, the shape change induced plasmon resonance spectral peak shift will become important. In order to obtain only the wavelength shift values caused by the shape change of the NPs, the RI of medium surrounding the gold NPs is set at a constant of 1.45 and the RI of the gold NP is assumed unchanged. The T-matrix method is used to calculate the scattered light and light extinction by the NP morphing. The diameters of the gold NPs are set from 100 nm to 400 nm, with the size interval at 10 nm, to cover a wide size range for typical sizes of gold spherical NPs. The spectra of the light scattering and light extinction were calculated on the Delft University high performance computing cluster. The results show that the plasmon resonance spectral peak shift is related to the size of the NPs. Larger sizes of gold NPs have larger peak shift values, but there is an inflection point around 200 nm and the bandwidth of the resonance peak becomes larger which will cause a difficulty in precisely locating the peak.","gold nanoparticle; plasmon resonance; spectral shift; Strain sensing","en","conference paper","SPIE","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2022-11-28","","","Structural Integrity & Composites","","",""
"uuid:0b88b900-a31d-4ec4-b08a-c8a56a73e970","http://resolver.tudelft.nl/uuid:0b88b900-a31d-4ec4-b08a-c8a56a73e970","Erratum to “Unraveling the myth of closure corrections: Sharpening the definition of opening and closure stresses with an energy approach” [Int. J. Fatigue 143 (2021) 106016] (International Journal of Fatigue (2021) 143, (S014211232030548X), (10.1016/j.ijfatigue.2020.106016))","van Kuijk, J.J.A. (TU Delft Structural Integrity & Composites); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2021","An important figure was omitted from this article, as Fig. 11 was repeated in Fig. 12. The image below shows the correct version of Fig. 12 that should have appeared in the article. [Figure presented]","","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:44794587-66f0-4f0a-876f-cb3716468b0a","http://resolver.tudelft.nl/uuid:44794587-66f0-4f0a-876f-cb3716468b0a","Modelling of light scattering by gold nanoparticles at optical fibre interfaces","Wang, X. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites)","","2021","Optical fibre backscatter reflectometry is an important technique for Structural Health Monitoring (SHM). In recent years, increasing the intensity of backscattered light in backscatter reflectometry has shown the advantage of improving the signal detection in shape sensing and temperature detection due to the increase of signal to noise ratio and this approach could potentially be used to improve the performance of an SHM system. Doping nanoparticles (NPs) is a method to increase the intensity of backscattered light in distributed fibre optic sensing. The increased intensity of light backscattered by the NPs needs to be investigated to design suitable optical sensing fibres with NPs for backscatter reflectometry. In this work NPs were added to refractive index matching liquid and tested with commercial NP suspensions experimentally between the tips of two optical fibres. An estimate of the intensity of backscattered light from the NPs in this structure was performed by simulation to give a better understanding of the expected levels of intensities of scattered light from NPs in this distributed fibre optic sensing configuration. We present analytical models based on Mie theory and the Monte Carlo Method. Simulated results are presented, for a broad bandwidth Gaussian spectra shape incident light with a central wavelength around 1550 nm, to match the experimental conditions in this work. The novelty is in developing this model for scattered light by NPs at optical fibre interfaces and the evaluation of the possibility of detection by the calculated scattered intensity levels.","backscattering; gold nanoparticle suspension; light scattering model; optical fibre","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:74b9e1be-7060-496e-b1ea-c3ac9d910b26","http://resolver.tudelft.nl/uuid:74b9e1be-7060-496e-b1ea-c3ac9d910b26","Damage accumulation analysis of cfrp cross-ply laminates under different tensile loading rates","Li, X. (TU Delft Structural Integrity & Composites); Saeedifar, M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites)","","2021","This paper investigates the loading rate effect on both mechanical properties and damage accumulation process of [0°2/90°4]S carbon fiber-polymer laminates under tensile loading. In-situ edge observations, Acoustic Emission and Digital Image Correlation techniques were utilized simultaneously to monitor the state of damage in real time. Results showed that the axial modulus and strength were less sensitive to loading rates than failure strain, which increased with the decrease of the loading rate. In the viewpoint of damage accumulation process, high density and uniform distribution of transverse matrix cracks, and H-shape crack patterns, incorporating inter-laminar cracks, were more likely to occur at low loading rates while variable crack spacing occurred at higher rates. When loading rates were lower than a certain level, maximum transverse matrix crack density decreased slightly due to the restriction of relatively widely generated inter-laminar cracks. Furthermore, the cumulative acoustic emission energy of low-frequency signals was linearly correlated to transverse matrix crack density, providing a promising way to quantify crack accumulation in real time. Finally, spatial consistence was observed between transverse matrix cracks at edges and stress concentrations at the exterior 0° ply, and the peaks of axial strain at local concentration regions locate either near the newest cracks or at the place with minimum crack spacing.","Acoustic emission; Cross-ply laminate; Digital image correlation; Inter-laminar crack; Transverse matrix crack","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:199b5aae-fd5d-4cf2-b1d8-5b43a11d68ea","http://resolver.tudelft.nl/uuid:199b5aae-fd5d-4cf2-b1d8-5b43a11d68ea","A Study on Through-the-Thickness Heating in Continuous Ultrasonic Welding of Thermoplastic Composites","Jongbloed, B.C.P. (TU Delft Aerospace Structures & Computational Mechanics); Teuwen, Julie J.E. (TU Delft Aerospace Manufacturing Technologies); Benedictus, R. (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Aerospace Structures & Computational Mechanics)","","2021","Continuous ultrasonic welding is a promising technique for joining thermoplastic composites structures together. The aim of this study was to gain further insight into what causes higher through-the-thickness heating in continuous ultrasonic welding of thermoplastic composites as compared to the static process. Thermocouples were used to measure temperature evolutions at the welding interface and within the adherends. To understand the mechanisms causing the observed temperature behaviours, the results were compared to temperature measurements from an equivalent static welding process and to the predictions from a simplified heat transfer model. Despite the significantly higher temperatures measured at the welding interface for the continuous process, viscoelastic bulk heat generation and not thermal conduction from the interface was identified as the main cause of higher through-the-thickness heating in the top adherend. Interestingly the top adherend seemed to absorb most of the vibrational energy in the continuous process as opposed to a more balanced energy share between the top and bottom adherend in the static process. Finally, the higher temperatures at the welding interface in continuous ultrasonic welding were attributed to pre-heating of the energy director due to the vibrations being transmitted downstream of the sonotrode, to reduced squeeze-flow of energy director due to the larger adherend size, and to heat flux originating downstream as the welding process continues.","fusion bonding; heat transfer; energy director; CF/PPS; joining; high-frequency welding","en","journal article","","","","","","","","","","","Aerospace Structures & Computational Mechanics","","",""
"uuid:f5bb3778-f91f-4172-8609-09ef713439de","http://resolver.tudelft.nl/uuid:f5bb3778-f91f-4172-8609-09ef713439de","Fusion-based damage diagnostics for stiffened composite panels","Broer, Agnes A.R. (TU Delft Structural Integrity & Composites); Galanopoulos, Georgios (University of Patras); Benedictus, R. (TU Delft Structural Integrity & Composites); Loutas, Theodoros (University of Patras); Zarouchas, D. (TU Delft Structural Integrity & Composites)","","2021","Conducting damage diagnostics on stiffened panels is commonly performed using a single SHM technique. However, each SHM technique has both its strengths and limitations. Rather than straining the expansion of single SHM techniques going beyond their intrinsic capacities, these strengths and limitations should instead be considered in their application. In this work, we propose a novel fusion-based methodology between data from two SHM techniques in order to surpass the capabilities of a single SHM technique. The aim is to show that by considering data fusion, a synergy can be obtained, resulting in a comprehensive damage assessment, not possible using a single SHM technique. For this purpose, three single-stiffener carbon–epoxy panels were subjected to fatigue compression after impact tests. Two SHM techniques monitored damage growth under the applied fatigue loads: acoustic emission and distributed fiber optic strain sensing. Four acoustic emission sensors were placed on each panel, thereby allowing for damage detection, localization, type identification (delamination), and severity assessment. The optical fibers were adhered to the stiffener feet’ surface, and its strain measurements were used for damage detection, disbond localization, damage type identification (stiffness degradation and disbond growth), and severity assessment. Different fusion techniques are presented in order to integrate the acoustic emission and strain data. For damage detection and severity assessment, a hybrid health indicator is obtained by feature-level fusion while a complementary and cooperative fusion of the diagnostic results is developed for damage localization and type identification. We show that damage growth can be monitored up until final failure, thereby performing a simultaneous damage assessment on all four SHM levels. In this manner, we demonstrate that by proposing a fusion-based approach toward SHM of composite structures, the intrinsic capacity of each SHM technique can be utilized, leading to synergistic effects for damage diagnostics.","Damage diagnostics; fusion; acoustic emission; distributed strain sensing; stiffened composite panel; fatigue; impact","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:b79a2259-33c5-43ee-b168-8c802e8fd0bf","http://resolver.tudelft.nl/uuid:b79a2259-33c5-43ee-b168-8c802e8fd0bf","Modeling and imaging of ultrasonic array inspection of side drilled holes in layered anisotropic media","Anand, C. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2021","There has been an increase in the use of ultrasonic arrays for the detection of defects in composite structures used in the aerospace industry. The response of a defect embedded in such a medium is influenced by the inherent anisotropy of the bounding medium and the layering of the bounding medium and hence poses challenges for the interpretation of the full matrix capture (FMC) results. Modeling techniques can be used to understand and simulate the effect of the structure and the defect on the received signals. Existing modeling techniques, such as finite element methods (FEM), finite difference time domain (FDTD), and analytical solutions, are computationally inefficient or are singularly used for structures with complex geometries. In this paper, we develop a novel model based on the Gaussian-based recursive stiffness matrix approach to model the scattering from a side-drilled hole embedded in an anisotropic layered medium. The paper provides a novel method to calculate the transmission and reflection coefficients of plane waves traveling from a layered anisotropic medium into a semi-infinite anisotropic medium by combining the transfer matrix and stiffness matrix methods. The novelty of the paper is the developed model using Gaussian beams to simulate the scattering from a Side Drilled Hole (SDH) embedded in a multilayered composite laminate, which can be used in both immersion and contact setups. We describe a method to combine the scattering from defects with the model to simulate the response of a layered structure and to simulate the full matrix capture (FMC) signals that are received from an SDH embedded in a layered medium. The model-assisted correction total focusing method (MAC-TFM) imaging is used to image both the simulated and experimental results. The proposed method has been vali-dated for both isotropic and anisotropic media by a qualitative and quantitative comparison with experimentally determined signals. The method proposed in this paper is modular, computationally inexpensive, and is in good agreement with experimentally determined signals, and it enables us to understand the effects of various parameters on the scattering of a defect embedded in a layered anisotropic medium.","CFRP; Full matrix capture; Gaussian beam; Side-drilled hole; Total focusing method; Ultrasonic phased array","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:50f26202-a389-401d-9668-496e5311ed42","http://resolver.tudelft.nl/uuid:50f26202-a389-401d-9668-496e5311ed42","Unraveling the myth of closure corrections: Sharpening the definition of opening and closure stresses with an energy approach","van Kuijk, J.J.A. (TU Delft Structural Integrity & Composites); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2021","The substantiation of fatigue crack closure corrections is disputed, based on the closure stress definition. The ΔKeff equation lacks a physical explanation. An inconsistency is observed between the opening stress Sopphen as used by this equation and the physical opening stress Sopphys. This Sopphys is related to Sopphen through an energy equivalent area approach. Furthermore, an elastic spring model is used as a physical approach to crack closure effects. An FEA approach generates Sopphys values, which are reworked into Sopphen. This physical model agrees well with existing closure corrections, and is able to provide a physical explanation for their necessity.","Closure corrections; Crack closure; Crack opening; Crack opening stress; Physics based approach","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:5189a4bb-f45a-45f8-ad5d-94a3d6909f2c","http://resolver.tudelft.nl/uuid:5189a4bb-f45a-45f8-ad5d-94a3d6909f2c","Optimization of light scattering enhancement by gold nanoparticles in fused silica optical fiber","Wang, X. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites)","","2021","A conventional distributed fiber optic sensing system offers close to linear sensitivity along the fiber length. However gold nanoparticles (NP) have been shown to be able to enhance the contrast ratio to improve the quality of signal detection. The challenge in improving the contrast of reflected signals is to optimise the nanoparticle doping concentration over the densed sensing length to make best use of the distributed fiber sensing hardware. In this paper, light enhancement by spherical gold NPs in the optical fibers was analyzed by considering the size-induced NP refractive index changes. This was achieved by building a new model to relate backscattered light from a gold NP suspension between the optical fiber end tips and backscattered light from gold NPs in the core of the optical fiber. The paper provides a model to determine the optimized sizes and concentrations of NPs for sensing at different desired penetration depths in the optical fiber.","","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:c888dc5a-6d7c-45e4-8111-76eabb0218dd","http://resolver.tudelft.nl/uuid:c888dc5a-6d7c-45e4-8111-76eabb0218dd","Measuring crack growth and related opening and closing stresses using continuous potential drop recording","van Kuijk, J.J.A. (TU Delft Structural Integrity & Composites); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2021","To improve resolution of in-situ measurement of crack closure and opening in fatigue, potential drop (PD) measurement technique has been further developed to measure thousands of times through each load cycle with high precision. The results are interpreted with physical phenomena like strain, Poisson's effect, piezo-resistivity, plasticity, and crack growth. Application of the technique to fatigue crack growth tests on aluminum 2024-T3 CCT specimens at different maximum stresses and stress ratios, demonstrate that indeed variations in PD can be associated to development of plasticity and crack opening and closure. Hence, the technique allows to measure timing and magnitude of crack opening and closure stresses in-situ in fatigue crack growth experiments.","Crack closure; Piezoresistivity; Plasticity; Poisson effect; Potential drop","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:bf32dc6e-b870-42b4-9d92-97522fb7967d","http://resolver.tudelft.nl/uuid:bf32dc6e-b870-42b4-9d92-97522fb7967d","Perception modelling by invariant representation of deep learning for automated structural diagnostic in aircraft maintenance: A study case using DeepSHM","Ewald, Vincentius (TU Delft Structural Integrity & Composites); Sridaran Venkat, Ramanan (Saarland University); Asokkumar, Aadhik (Saarland University; Kaunas University of Technology); Benedictus, R. (TU Delft Structural Integrity & Composites); Boller, Christian (Saarland University); Groves, R.M. (TU Delft Structural Integrity & Composites)","","2021","Predictive maintenance, as one of the core components of Industry 4.0, takes a proactive approach to maintain machines and systems in good order to keep downtime to a minimum and the airline maintenance industry is not an exception to this. To achieve this goal, practices in Structural Health Monitoring (SHM) complement the existing Non-Destructive-Testing (NDT) have been established in the last decades. Recently, the increasing computational capability such as utilization of a graphical processing unit (GPU) in combination with advanced machine learning techniques such as deep learning has been one of the main drivers in the advancement of predictive analytics in condition monitoring. In our previous work, we proposed a novel approach using deep learning for guided wave based structural health called DeepSHM. As a study case, we treated an ultrasonic signal from guided Lamb wave SHM with a convolutional neural network (CNN). In that work, we only considered a single central frequency excitation. This led to a single governing wavelength which is normally good for the detection of a single damage size. In classical signal processing, applying a broader excitation frequency poses an analysis and interpretation nightmare because it contains more complex information and thus is difficult to understand. This problem can be overcome with deep learning; however, it creates another problem: while deep learning typically results in a more accurate result prediction, it is specifically made for solving only certain types of tasks. While many papers have already introduced deep learning for diagnostics, many of these works are only proposing novel predictive techniques, however the mathematical formalization is lacking, and we are not informed about why we should treat acoustic signal with deep learning. So, the basis of ‘explainable AI’ for SHM and NDT is currently lacking. For this reason, in this paper, we would like to extend our previous work into a more generalized. Rather than focusing on a novel technique, we propose a plausible theoretical perspective inspired from neuroscience for signal representation of deep learning framework to model machine perception in structural health monitoring (SHM), especially because SHM typically involves multiple sensory input from different sensing locations. To do this, we created a set of artificial data from a finite element model (FEM) and represented DeepSHM in two different ways: 1). Perpetual representation of observation and 2). Hierarchical structure of entities that is decomposable in a smaller sub-entity. Consequently, we assume two plausible models for DeepSHM: 1). Either it behaves as a single deciding actor since the observation is regarded as perpetual, and 2). Or it acts as a multiple actor with independent outputs since multiple sensors can form different output probabilities. These artificial data were split into several different input representations, classified into several damage scenarios and then trained with commonly used deep learning training parameters. We compare the performance metrics of each perception model to describe the training behavior of both representations.","Convolutional neural network; Deep learning; Feature learning; Invariant representation; Perception; Structural health monitoring; Time-frequency-analysis; Ultrasonic lamb wave","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:76551aec-50e4-4bba-b12d-a8ff73327abc","http://resolver.tudelft.nl/uuid:76551aec-50e4-4bba-b12d-a8ff73327abc","On the sensitivity of ultrasonic welding of epoxy- to polyetheretherketone (PEEK)-based composites to the heating time during the welding process","Tsiangou, E. (TU Delft Aerospace Structures & Computational Mechanics); Kupski, J.A. (TU Delft Structural Integrity & Composites); Teixeira De Freitas, S. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Aerospace Structures & Computational Mechanics)","","2021","This study aims at assessing the sensitivity of the ultrasonic welding process for joining epoxy- to thermoplastic-based composites sensitivity to the heating time. For that, carbon fibre (CF)/epoxy adherends with a co-cured PEI coupling layer were ultrasonically welded to CF/polyetheretherketone (PEEK) adherends at different heating times. Process-induced changes in the meso and microstructure of these welds were identified and correlated to the weld strength. Subsequently, a processing interval, i.e., a range of heating times resulting in less than 10% decrease of weld strength, was defined. As, expected, the dissimilar composite welded joints were more sensitive to the heating time than the CF/PEEK to CF/PEEK welded joints. However, this effect was less pronounced than expected, since a relatively wide processing interval could be obtained provided that the coupling layer had a sufficient thickness.","A. Polymer-matrix composites (PMCs); A. Thermoplastic resin; A. Thermosetting resin; E. Joints/joining","en","journal article","","","","","","","","","","","Aerospace Structures & Computational Mechanics","","",""
"uuid:a688376d-2c9b-4ed6-bc39-9bc3f155d01d","http://resolver.tudelft.nl/uuid:a688376d-2c9b-4ed6-bc39-9bc3f155d01d","Light scattering by gold nanoparticles cured in optical adhesive at optical fibre interfaces","Wang, X. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites)","Lehmann, Peter (editor); Osten, Wolfgang (editor); Goncalves, Armando Albertazzi (editor)","2021","This study forms a part of the research in using nanoparticles (NPs) to increase the intensity of light scattering signal in the optical fibres. Increasing the intensity of the backscattered light signal in the optical fibres shows the potential to increase the signal-to-noise ratio in order to improve the sensitivity of the backscatter reflectometry. Doping NPs into the optical fibres can greatly increase the scattered light. However, it is not easy to manufacture NP-doped optical fibres to test different designs. To overcome this problem, in our former work we used the method of dropping refractive index matching liquid containing gold NPs at the optical fibres end tips to investigate the intensity change of the scattered light from the interfaces. In this paper, some new initial experimental results for the scattered light between the optical fibre end tips are shown. Gold NPs have been mixed into the optical adhesive (Norland) and is then dropped and cured at the optical fibre end tips. A backscatter reflectometer (LUNA ODiSI-B) was used in the experiment to measure the intensity of scattered light distribution between the optical fibre end tips. We investigated 4 cases of light scattering between the optical fibre end tips: (i) the backscattered light intensity distribution in the case of the air gap between the optical fibre end tips; (ii) the backscattered light intensity distribution with optical adhesive between the optical fibre end tips; (iii) the backscattered light intensity distribution with optical adhesive containing gold NPs (gold nanopowder (<100 nm), Sigma Aldrich) between the optical fibre end tips before curing process and (iv) the backscattered light intensity distribution with optical adhesive containing gold NPs between the optical fibre end tips after the curing process. Our initial findings are that the scattered light by gold NPs at the optical fibre interfaces can be detected by the backscatter reflectometer. By obtaining the differential signal between the distributed light scattering by cured optical adhesive containing gold NPs and only optical adhesive between the optical fibre end tips, the light scattered by the gold NPs has be determined.","Curing process; Gold nanoparticle; Light scattering; Optical adhesive","en","conference paper","SPIE","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2022-04-12","","","Structural Integrity & Composites","","",""
"uuid:04f3f191-8486-4745-a6a0-d799b6146092","http://resolver.tudelft.nl/uuid:04f3f191-8486-4745-a6a0-d799b6146092","Thermal effects on the performance of ultrasonically welded CF/PPS joints and its correlation to the degree of crystallinity at the weldline","Koutras, N. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Aerospace Structures & Computational Mechanics)","","2021","The effect of temperature on the lap shear strength (LSS) and failure mechanisms of ultrasonically welded carbon fibre reinforced polyphenylene sulphide (CF/PPS) joints was investigated, correlating the weld performance to the crystallinity degree of PPS at the weldline. The single-lap shear tests were carried out at temperatures ranging from –50 °C to 120 °C on three series, one with amorphous and two with semi-crystalline weldline. The overall trend was decreasing LSS with increasing temperature and the largest LSS reduction was observed above the glass transition temperature. Fractographic analysis revealed that the main failure mechanism at –50 °C was matrix fracture while fibre/matrix debonding became more pronounced with increasing temperature. It was demonstrated that higher degree of crystallinity of PPS at the weldline was beneficial at high temperatures (90 °C and 120 °C) most likely due to the higher fibre/matrix interfacial strength compared to amorphous PPS. The amorphous weldline was shown to be advantageous at -50 °C, probably due to the higher toughness and ductility of amorphous PPS.","Crystallinity; Failure mechanism; Temperature; Thermal analysis; Thermoplastic composites; Ultrasonic welding","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:bfe96ada-1ed2-437c-9472-2e952ac44e8b","http://resolver.tudelft.nl/uuid:bfe96ada-1ed2-437c-9472-2e952ac44e8b","Experimental method for investigating wear of porous thermal insulation systems exposed to realistic, hot, turbulent gas flow","Reurings, C. (TU Delft Structural Integrity & Composites); Koussios, S. (TU Delft Aerospace Manufacturing Technologies); Bergsma, O.K. (TU Delft Structural Integrity & Composites); Vergote, K. (BOSAL ECS n.v.); Paeshuyse, L. (BOSAL ECS n.v.); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2021","A realistic wear test was developed for porous thermal insulation systems exposed to high temperature turbulent gas flow, because it is essential for the development of existing and new concepts of such insulation and therefore also for the performance of processes that depend on such insulation. Wear is crucial and often dominant for the long-term performance of thermal insulation and, because of the complex nature of insulation wear under exposure of high-temperature turbulent flow, realistic testing capability is a necessary tool for improvement. A test rig was developed to subject fibrous ceramic insulation, the most encountered type of thermal insulation, to conditions representative for in-service use and to enable investigation of the occurring phenomena and behaviour. This rig can accommodate a range of different insulation configurations and is compatible with many turbulent flow sources. This test rig, its components, the experimental procedure, its accuracy and representative results are presented.","High temperature; porous thermal insulation; Pulsating; Testing; Turbulent flow; Wear","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:8485f597-d62f-4bc4-b59d-ff604e1a48f0","http://resolver.tudelft.nl/uuid:8485f597-d62f-4bc4-b59d-ff604e1a48f0","On the sensitivity of the ultrasonic welding process of epoxy- to polyetheretherketone (PEEK)-based composites to the welding force and amplitude of vibrations","Tsiangou, E. (TU Delft Aerospace Structures & Computational Mechanics); Teixeira De Freitas, S. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Aerospace Structures & Computational Mechanics)","","2021","This paper addresses the sensitivity of the ultrasonic welding process for joining dissimilar composites to variations in either the welding force or amplitude of vibrations. For that, carbon fibre (CF)/epoxy specimens were welded to CF/polyetheretherketone (PEEK) specimens, through a polyetheretherimide (PEI) coupling layer co-cured with the CF/epoxy material. It was found that reducing either the welding force or the amplitude of vibrations caused an increase in the heating time and maximum temperatures between the coupling layer and CF/epoxy adherend. In addition, local signs of thermal degradation were found in the CF/epoxy adherend even at welding conditions that resulted in the highest strength. However, such alterations were not significant enough to have an apparent effect on the maximum lap shear strength of the welded joints.","Joints/joining; Polymer-matrix composites (PMCs); Thermoplastic resin; Thermosetting resin; Ultrasonic welding","en","journal article","","","","","","","","","","","Aerospace Structures & Computational Mechanics","","",""
"uuid:96fe92b2-7fc9-41e9-bd68-440fa924aa03","http://resolver.tudelft.nl/uuid:96fe92b2-7fc9-41e9-bd68-440fa924aa03","Multi-material adhesive joints with thick bond-lines: Crack onset and crack deflection","Lopes Fernandes, R. (TU Delft Structural Integrity & Composites); Budzik, Michal K. (Aarhus University); Benedictus, R. (TU Delft Structural Integrity & Composites); Teixeira De Freitas, S. (TU Delft Structural Integrity & Composites)","","2021","This study investigates the fracture onset and crack deflection in multi-material adhesive joints with thick bond-lines (≈10 mm) under global mode I loading. The role of adherend-adhesive modulus-mismatch and pre-crack length are scrutinized. The parameters controlling the crack path directional stability are also discussed. Single-material (i.e. steel-steel and GFRP-GFRP) and bi-material (i.e. steel-GFRP) double-cantilever beam joints bonded with a structural epoxy adhesive are tested. The joints are modelled analytically, considering a beam on elastic-plastic foundation, to include characteristic length scales of the problem (e.g. adhesive thickness, plastic zone) and numerically using Finite Element Model. An empirical relation, in terms of geometrical and material properties of the joints, that defines the transition between non-cohesive and cohesive fracture onset is found. Above a specific pre-crack length the stress singularity at pre-crack tip rules over the stress singularity near bi-material corners, resulting in mid-adhesive thickness cohesive fracture onset. However, the cracking direction rapidly deflects out from the adhesive layer centre-line. Positive T-stress along the crack tip is found to be one of the factors for the unstable crack path.","Fracture onset; Mode I; Thick bond-line","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:ef946695-37da-4072-a07a-8a7882345eb8","http://resolver.tudelft.nl/uuid:ef946695-37da-4072-a07a-8a7882345eb8","Damage Diagnostics of a Composite Single-Stiffener Panel Under Fatigue Loading Utilizing SHM Data Fusion","Broer, Agnes A.R. (TU Delft Structural Integrity & Composites); Galanopoulos, Georgios (University of Patras); Zarouchas, D. (TU Delft Structural Integrity & Composites); Loutas, Theodoros (University of Patras); Benedictus, R. (TU Delft Structural Integrity & Composites)","Rizzo, Piervincenzo (editor); Milazzo, Alberto (editor)","2021","A case study is presented in which the first steps are made towards the development of a structural health monitoring (SHM) data fusion framework. For this purpose, a composite single-stiffener panel is subjected to compression-compression fatigue loading (R = 10). The carbon-epoxy panel contains an artificial disbond of 30 mm, which was created using a Teflon insert during manufacturing and placed between the skin and the stiffener foot. Under the applied fatigue load, the disbond is expected to grow and its propagation is monitored using two SHM techniques, namely acoustic emission (AE) and Rayleigh-scattering based distributed fiber optic strain sensing. Four AE sensors are placed on the skin, thereby allowing for disbond growth detection and localization. On each stiffener foot, fiber optic sensors are surface-bonded to monitor the growth of the disbond under the applied fatigue loading. The distributed strain measurements are used to localize and monitor the disbond growth. The strength of each technique is utilized by fusing the data from the AE sensors and the fiber optic sensors. In this manner, a data-driven approach is presented in which a data fusion of the different techniques allows for monitoring the damage in the stiffened panel on multiple SHM levels, including disbond growth detection and localization.","Acoustic emission; Composite single-stiffener panel; Data fusion; Distributed strain sensing; Fatigue loading","en","conference paper","Springer","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2022-06-28","","","Structural Integrity & Composites","","",""
"uuid:1c7a59e3-7039-43e2-a1a1-d273ed9d0c41","http://resolver.tudelft.nl/uuid:1c7a59e3-7039-43e2-a1a1-d273ed9d0c41","On differences and similarities between static and continuous ultrasonic welding of thermoplastic composites","Jongbloed, B.C.P. (TU Delft Aerospace Manufacturing Technologies); Teuwen, Julie J.E. (TU Delft Aerospace Manufacturing Technologies); Benedictus, R. (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Aerospace Structures & Computational Mechanics)","","2020","Continuous ultrasonic welding is a promising high-speed and energy-efficient joining method for thermoplastic composite structures. Our aim was to identify and understand differences between the static and continuous ultrasonic welding process for thermoplastic composites. In particular, melting of the interface, consumed power and energy density, temperature evolution at the weld interface, and optimum welding conditions for both types of processes were investigated. This was done for three combinations of welding force and vibrational amplitude, parameters which are known to have a significant effect in both welding processes. Our results showed that for the continuous process the amount of non-welded area under the sonotrode remains constant, while for the static process the amount of non-welded area gradually decreases to zero. Additionally, the optimum vibration times and welding speeds in both processes are similar.","fusion bonding; Polymer mesh; Continuous welded seam; High frequency welding; Joining; Fusion bonding","en","journal article","","","","","","","","","","","Aerospace Manufacturing Technologies","","",""
"uuid:84eaa7e0-19a2-4d87-89c2-d50db4eec6f1","http://resolver.tudelft.nl/uuid:84eaa7e0-19a2-4d87-89c2-d50db4eec6f1","On the influence of overlap topology on the tensile strength of composite bonded joints: Single overlap versus overlap stacking","Kupski, J.A. (TU Delft Structural Integrity & Composites); Teixeira De Freitas, S. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","The goal of this study is to explore new topologies for adhesively bonded composite overlap joints in order to improve their strength under tensile loading. Multiple stacked overlaps, also referred as finger joints, are compared with single overlap topologies. The quasi-static tensile behaviour of single lap joints with two overlap lengths 12.7 mm and 25.4 mm are compared to finger joints with 1 and 2 stacked overlaps through thickness with constant 12.7 mm overlap length. Two composite adherend stacking sequences are tested for each topology [0/90]4s and [90/0]4s. A non-linear FE-analysis is performed to analyse the shear and peel stresses along the adhesive bond line. A difference in peak shear and peel stress, at the tip of the bonded region could be observed: (i) for 1 finger, the peak peel stress is higher than in the single lap joint configurations because the beneficial effect of avoiding eccentricity in the finger joint is outperformed by the detrimental effect of reducing to half the adherend stiffness at the overlap; (ii) for 2 fingers, the stress field changes significantly leads to a 23% decrease in peak shear and 33% in peak peel stress, compared to the single lap joint topologies. In addition, experimental lap shear tests are performed and monitored using acoustic emission technique, to follow the damage events. Different trends at damage initation and at maximum load are believed to result from how the damage propagates inside the joint. A topology with 2 fingers and layup [90/0]4s, which fails entirely inside the adherend, provides the lowest peak shear and peel stress and the highest load at damage initiation. It is however outperformed in maximum load by a single lap joint topology with layup [0/90]4s, with mostly cohesive failure. It is further found that, unlike in single overlap topologies, the most dominant stress component for damage initiation inside the finger joints is the in-plane tensile stress, at the butt joint resin pockets, rather than peel stresses at the overlap region. Lastly, if weight efficiency is the main requirement, a finger joint design can effectively replace a single overlap joint design. However, for absolute maximum joint strength, the single overlap joint is a better choice than the finger joint.","Adhesive bonding; Composite joints; Finger joints; Joint topology; ply interleaving technique","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:b707be28-4268-4a0a-9e99-60158d81dd16","http://resolver.tudelft.nl/uuid:b707be28-4268-4a0a-9e99-60158d81dd16","Role of adherend material on the fracture of bi-material composite bonded joints","Lopes Fernandes, R. (TU Delft Structural Integrity & Composites); Teixeira De Freitas, S. (TU Delft Structural Integrity & Composites); Budzik, Michal K. (Aarhus University); Poulis, J.A. (TU Delft Adhesion Institute); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","The aim of this study is to investigate the effect of the adherend material on the mode I fracture behaviour of bi-material composite bonded joints. Both single-material (steel-steel and composite-composite) and bi-material (steel-composite) joints bonded with a structural epoxy adhesive are studied. Additionally, two adhesive bondline thicknesses are considered: 0.4 mm (thin bondline) and 10.1 mm (thick bondline). The Penado-Kanninen reduction scheme is applied to evaluate the mode I strain energy release rate. The results show that the mode I fracture energy, GIc, is independent of the adherend type and joint configuration (single or bi-material). GIc shows average values between 0.60 and 0.72 N/mm for thin bondlines and 0.90–1.10 N/mm for thick bondlines. For thin bondlines, the failure is cohesive and the similar degree of constraint that is imposed to the adhesive by the high-modulus (i.e., steel) and/or relatively thick (i.e., composite) adherends results in similar values of GIc for both single- and bi-material joint types. For thick bondlines, the crack grows closer to one of the adhesive-adherend interfaces, but still within the adhesive. The results show that the adhesive could deform similarly, although the crack has been constrained on one side by different types of adherends, either a steel or composite.","Adherend material; Analytical modelling; Mode I fracture; Steel-composite bonded joints","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:52f34753-3bca-4dc0-94ae-5d202690104d","http://resolver.tudelft.nl/uuid:52f34753-3bca-4dc0-94ae-5d202690104d","Enhancing the fracture toughness of carbon fibre/epoxy composites by interleaving hybrid meltable/non-meltable thermoplastic veils","Quan, D. (TU Delft Structural Integrity & Composites); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Dransfeld, C.A. (TU Delft Aerospace Manufacturing Technologies); Murphy, Neal (University College Dublin); Ivanković, Alojz (University College Dublin); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","Interlaying thermoplastic veils into carbon fibre/epoxy composites has proved to significantly increase the interlaminar fracture toughness. The main toughening mechanism is thermoplastic fibre bridging for the non-meltable veils and matrix toughening for the meltable veils. Herein, to take advantage of different toughening mechanisms, hybrid meltable/non-meltable thermoplastic veils were used to interlay two types of aerospace-grade composites produced from unidirectional (UD) prepregs and resin transfer moulding of non-crimp carbon fibre fabrics (NCF). The mode-I and mode-II fracture behaviour of the interleaved laminates were investigated. The experimental results demonstrated outstanding toughening performance of the hybrid veils for the mode-I fracture behaviour of the UD laminates and for both of the mode-I and mode-II fracture behaviour of the NCF laminates, resulting from the combination of different toughening mechanisms. For example, the maximum increases in the mode-I and mode-II fracture energies of the NCF laminates were observed to be 273% and 206%, respectively.","Carbon fibre/epoxy composites; Fracture toughness.; Hybrid toughening; Thermoplastic veils","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:562cc6d4-71cb-46bc-92b5-f22991937c79","http://resolver.tudelft.nl/uuid:562cc6d4-71cb-46bc-92b5-f22991937c79","Co-cure joining of epoxy composites with rapidly UV-irradiated PEEK and PPS composites to achieve high structural integrity","Quan, D. (TU Delft Structural Integrity & Composites); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Dransfeld, C.A. (TU Delft Aerospace Manufacturing Technologies); Tsakoniatis, Ioannis (TU Delft Aerospace Manufacturing Technologies); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","Efficient joining of hybrid thermoset/thermoplastic composite joints is critical to produce high performance lightweight structures while keeping the cost low. Herein, a high-power UV-irradiation technique was proposed to rapidly active the surfaces of PEEK and PPS composites for the following co-cure joining with epoxy composites. A single lap-shear joint test and a double cantilever beam test were used to evaluate the mechanical and fracture performance of the hybrid joints. The experimental results revealed that high structural integrity of the hybrid joints was achieved upon applying a 6 s UV-treatment to the thermoplastic composites. For example, the lap-shear strength and fracture energy of the adhesive bonded hybrid joints were above 25 MPa and 800 J/m2, respectively. Overall, high-power UV-irradiation proved a highly efficient, rapid and low-cost method to treat thermoplastic composites for the co-cure joining with epoxy composites, and hence it demonstrated significant promise in industrial mass production.","Adhesive bonding; Hybrid composite joints; Structural integrity; Surface treatment","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:92d4a954-0e60-4a51-8b5f-f3a42627cfcf","http://resolver.tudelft.nl/uuid:92d4a954-0e60-4a51-8b5f-f3a42627cfcf","Unfolding the early fatigue damage process for CFRP cross-ply laminates","Li, X. (TU Delft Structural Integrity & Composites); Kupski, J.A. (TU Delft Structural Integrity & Composites); Teixeira De Freitas, S. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites)","","2020","This study investigates the early fatigue damage of cross-ply carbon/epoxy laminates. The aim is to unfold the damage accumulation process, understand the interaction between different damage mechanisms, and quantify their contribution to stiffness degradation. Tension-tension fatigue tests were performed, while edge observation and DIC technique monitored the damage evolution. It was found that different accumulation process and interactive levels between transverse matrix cracks and delamination exist for specimens with similar stiffness degradation. A linear increase of stiffness degradation was observed with the increase of matrix crack density, while the growing trend of stiffness degradation converged with the increase of delamination.","Damage interaction; Digital Image Correlation; Early fatigue damage process; In-situ monitoring","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:5632772d-07b4-402f-b138-349cc6b5ddc7","http://resolver.tudelft.nl/uuid:5632772d-07b4-402f-b138-349cc6b5ddc7","Significantly enhanced structural integrity of adhesively bonded PPS and PEEK composite joints by rapidly UV-irradiating the substrates","Quan, D. (TU Delft Structural Integrity & Composites); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Dransfeld, C.A. (TU Delft Aerospace Manufacturing Technologies); Tsakoniatis, Ioannis (TU Delft Aerospace Manufacturing Technologies); Teixeira De Freitas, S. (TU Delft Structural Integrity & Composites; University College Dublin); Scarselli, Gennaro (University College Dublin; University of Salento); Murphy, Neal (University College Dublin); Ivanković, Alojz (University College Dublin); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","A high-power UV-irradiation technique was proposed for the surface treatment of PPS and PEEK composites, aiming to achieve good adhesion with epoxy adhesives. The composite substrates were rapidly UV-irradiated for a duration of between 2–30s, and then bonded using an aerospace film adhesive to produce joints. Tensile lap-shear strength and mode-I and mode-II fracture energies of the adhesive joints were investigated. It was observed that the application of a short-time UV-irradiation to the substrates transformed the failure mode of the specimens from adhesion failure to substrate damage in all cases. This consequently resulted in remarkable improvements in the mechanical and fracture performance of the adhesive joints. For example, the lap-shear strength increased from 11.8MPa to 31.7MPa upon UV-irradiating the PPS composites for 3s, and from 8.3MPa to 37.3MPa by applying a 5s UV-irradiation to the PEEK composites. Moreover, the mode-I and mode-II fracture energies significantly increased from ∼50J/m2 to ∼1500J/m2 and from <300J/m2 to ∼7000J/m2, respectively for both of the adhesively bonded PEEK and PPS composite joints.","A: Adhesive joints; A: Polymer-matrix composites (PMCs); B: Fracture toughness; B: Strength; E: Welding/joining","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:8d99ac4a-7235-4250-992c-fc9f523f5295","http://resolver.tudelft.nl/uuid:8d99ac4a-7235-4250-992c-fc9f523f5295","Ultrasonic welding of epoxy- to polyetheretherketone- based composites: Investigation on the material of the energy director and the thickness of the coupling layer","Tsiangou, E. (TU Delft Aerospace Manufacturing Technologies); Teixeira De Freitas, S. (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Aerospace Structures & Computational Mechanics); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","Ultrasonic welding is a highly promising technique for joining thermoplastic to thermoset composites. A neat thermoplastic coupling layer is co-cured on the surface to be welded to make the thermoset composite ‘weldable’. A reliable bond is attained when miscible thermoplastic and thermoset materials are chosen. For welding carbon fibre/polyetheretherketone (PEEK) to thermoset composite samples, a PEEK film is not preferable due to its immiscibility with epoxy resins. On the other hand, polyetherimide is an excellent candidate, since it is known to be miscible to most epoxy systems at high temperatures and PEEK polymers. This study focusses on two main subjects; firstly, the nature of the material of the energy director, i.e. a flat thermoplastic film used to promote heat generation at the interface. In this case, the energy director can be either polyetherimide, as in the coupling layer or PEEK material, as in the matrix of the thermoplastic composite adherend. It was found that both materials can produce welds with similar mechanical performance. This study focusses secondly on the thickness of the coupling layer. Due to the high melting temperature of the PEEK matrix, a 60-µm-thick coupling layer was seemingly too thin to act as a thermal barrier for the epoxy resin for heating times long enough to produce fully welded joints. Such an issue was found to be overcome by increasing the thickness of the coupling layer to 250 µm, which resulted in high-strength welds.","Composites; thermoplastic; thermoset; ultrasonic welding","en","journal article","","","","","","","","","","","Aerospace Manufacturing Technologies","","",""
"uuid:f9f1e478-dc81-46d4-9da6-994888032ff4","http://resolver.tudelft.nl/uuid:f9f1e478-dc81-46d4-9da6-994888032ff4","A gaussian beam based recursive stiffness matrix model to simulate ultrasonic array signals from multi-layered media","Anand, C. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","Ultrasonic testing using arrays is becoming widely used to test composite structures in the Aerospace industry. In recent years, the Full Matrix Capture (FMC) technique has been implemented to extract the signals for post-processing to form an image. The inherent anisotropy and the layering of the structure pose challenges for the interpretation of this FMC data. To overcome this challenge, modeling techniques are required that take into account the diffraction caused by finite-size transducers and the response of the structure to these bounded beams. Existing models either homogenize the entire structure, use computationally expensive finite difference time domain (FDTD) methods, or do not consider the shape of the bounded beam, which is used to test such structures. This paper proposes a modeling technique based on combining the Multi-Gaussian beam model with the recursive stiffness matrix method to simulate the FMC signals for layered anisotropic media. The paper provides the steps required for the modeling technique, the extraction of the system efficiency factor, and validation of the model with experimentally determined signals for aluminum as an isotropic material such as aluminum and Carbon Fiber Reinforced Plastic (CFRP) laminate as a layered material. The proposed method is computationally inexpensive, shows good agreement with the experimentally determined FMC data, and enables us to understand the effects of various transducer and material parameters on the extracted FMC signals.","Angular spectrum; CFRP; Full matrix capture; Gaussian beam; Modeling; Recursive stiffness matrix","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:28af33d0-fdb2-45d7-8ba1-5783cbeb4d02","http://resolver.tudelft.nl/uuid:28af33d0-fdb2-45d7-8ba1-5783cbeb4d02","An adaptive probabilistic data-driven methodology for prognosis of the fatigue life of composite structures","Eleftheroglou, N. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","Data driven probabilistic methodologies have found increasing use the last decade and provide a platform for the remaining useful life (RUL) prediction of composite structures utilizing health-monitoring data. Of particular interest is the RUL prediction of composite structures that either underperform or outperform due to unexpected phenomena that might occur during their service life. These composite structures are referred as outliers and the prediction of their RUL is a challenge. This study addresses this challenge by proposing a new data-driven model; the Adaptive Non-Homogenous Hidden Semi Markov Model (ANHHSMM), which is an extension of the NHHSMM. The ANHHSMM uses diagnostic measures, which are estimated based on the training and testing data, and it adapts the trained parameters of the NHHSMM. The training data set consists of acoustic emission data collected from open-hole carbon–epoxy specimens, subjected to fatigue loading, while the testing data set consists of acoustic emission data collected from specimens, subjected to fatigue and in-situ impact loading, which can be considered as an unseen event for the training process. ANHHSMM provides better predictions in comparison to the NHHSMM for all the cases, demonstrating its capability to adapt to unexpected phenomena and integrate unforeseen data to the prognostics course.","Acoustic emission; Adaptation; Probabilistic data-driven methodology; Prognostics; Remaining useful life","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:c3a34572-0191-4638-90e3-7a50877be146","http://resolver.tudelft.nl/uuid:c3a34572-0191-4638-90e3-7a50877be146","The influence of a porous, compliant layer with overlying discrete roughness elements as exhaust pipe wall on friction and heat transfer","Reurings, C. (TU Delft Structural Integrity & Composites); Koussios, S. (TU Delft Aerospace Manufacturing Technologies); Bergsma, O.K. (TU Delft Structural Integrity & Composites); Breugem, W.P. (TU Delft Multi Phase Systems); Vergote, K. (BOSAL ECS n.v.); Paeshuyse, L. (BOSAL ECS n.v.); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","The purpose of this work is to experimentally establish the combined influence on the flow and thermal resistance of an exhaust pipe wall formed by a porous, compliant layer with overlying discrete roughness elements exposed to the pulsating exhaust gas flow of a combustion engine. Through measuring the streamwise pressure drop over and radial temperature differences in different pipe samples for a range of flow states with different Reynolds numbers and non-dimensional pulsation frequencies, the effects were discerned. The configurations of the sample walls covered a range of mesh pitches, compliant-layer densities, and compliant-layer compression ratios. The (non-sinusoidally) pulsating exhaust gas flow spanned the following range: Reb (= ubD/νb) = 1⋅ 104 - 3⋅ 104, Tb = 500 - 800 ∘C, ω+(= ωνb/uτ2) = 0.003 - 0.040. The friction factors were found to be effectively constant with Reynolds number and non-dimensional pulsation frequency while the variation with insulation density/compression was not significant. Additionally, for both mesh pitches, the measured friction factors were in line with those reported in literature for similar geometries with steady flow and solid walls. Together this indicates that neither compliance nor the pulsations in the exhaust gas flow significantly affect the friction for this configuration. Comparison of the samples based on the derived thermal resistance showed a similar influence of the fluid-wall interface as for the friction. Additionally a distinct influence of compression, independent of the insulation density, was observed that increases with increasing temperature. It was concluded that the increased resistance was due to additional radiation resistance because of fibre reorientation due to compression.","","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:0ad1147e-01c1-42e9-b5aa-877fd8181076","http://resolver.tudelft.nl/uuid:0ad1147e-01c1-42e9-b5aa-877fd8181076","The influence of interlayer/epoxy adhesion on the mode-I and mode-II fracture response of carbon fibre/epoxy composites interleaved with thermoplastic veils","Quan, D. (TU Delft Structural Integrity & Composites); Deegan, Brian (Henkel Ireland Operations & Research Ltd.); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Dransfeld, C.A. (TU Delft Aerospace Manufacturing Technologies); Murphy, Neal (University College Dublin); Ivanković, Alojz (University College Dublin); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","The compatibility between the majority of thermoplastic veils (TPVs) and epoxies is typically poor, owing to the inherently low surface energies of thermoplastics. This tends to largely affect the toughening performance of TPVs as interlayer materials of carbon fibre/epoxy composites. The traditional methods for surface activation of thermoplastics, such as corona discharge, plasma treatment and acid etches, are not applicable to TPVs as they could cause significant damage to the thermoplastic fibres with nano-/micro-scale diameters. Herein, a UV-irradiation technique was proposed to active the surfaces of polyphenylene-sulfide (PPS) veils, that effectively improved their adhesion with epoxies. Consequently, the effects of an improved veil/epoxy adhesion on the mode-I and mode-II fracture behaviour and corresponding fracture mechanisms of the interleaved laminates were investigated. It was found that an improved veil/epoxy adhesion significantly enhanced the toughening performance of the PPS veils for the laminates manufactured by resin transfer moulding of non-crimp fabrics, by introducing additional carbon fibre delamination and significant PPS fibre damage during the fracture process. In contrast, the increased level of veil/epoxy adhesion inhibited PPS fibre bridging during the fracture process of the laminates produced from unidirectional prepregs, and caused considerable adverse effects on the fracture performance.","Fracture toughness; Interlay toughening; Interlayer/matrix adhesion; Polymer-matrix composites; Thermoplastic veils","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:fd8eaebb-f942-4f11-b2d4-901099560754","http://resolver.tudelft.nl/uuid:fd8eaebb-f942-4f11-b2d4-901099560754","Effects of high-amplitude low-frequency structural vibrations and machinery sound waves on ultrasonic guided wave propagation for health monitoring of composite aircraft primary structures","Ochôa, Pedro (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","A reliable damage diagnostic by ultrasonic guided wave (GW) based structural health monitoring (SHM) can only be achieved if the physical interactions between wave propagation, the SHM system and environmental factors are fully understood. The purpose of this research was to gain knowledge about the effects of high-amplitude low-frequency structural vibrations (HA-LFV) and audible sound waves (SW) on ultrasonic GW propagation. Measurements were performed on a stiffened panel of a full-scale composite torsion box containing barely visible impact damage. Time-domain analysis of the filtered GW signals revealed that the main effect of HA-LFV was the presence of coherent noise. This was interpreted as the consequence of superposition of multiple dispersive wave groups produced by mode conversion at the moment of reflection on the corrugated panel surfaces during propagation. It was also observed that the coherent noise amplitude depends on the amplitude of the HA-LFV, and on the ratio between the HA-LFV frequency and the ultrasonic excitation frequency. These relationships can potentially be explored for the development of a HA-LFV compensation mechanism to enable in-service GW based damage diagnostics. In contrast, GW signals in the cases with audible SW present were almost unaffected. It was concluded that there is strong evidence supporting the hypothesis that ultrasonic GW propagation with HA-LFV effects can be analysed under the assumption of a permanently corrugated structure.","Aircraft primary structure; Composite materials; Low-frequency vibration; Structural health monitoring; Ultrasonic guided wave","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:309e9b11-6f3b-4444-99f2-1ccaa87aa01b","http://resolver.tudelft.nl/uuid:309e9b11-6f3b-4444-99f2-1ccaa87aa01b","Continuous ultrasonic welding of thermoplastic composites: Enhancing the weld uniformity by changing the energy director","Jongbloed, B.C.P. (TU Delft Aerospace Manufacturing Technologies); Teuwen, Julie J.E. (TU Delft Aerospace Manufacturing Technologies); Palardy, G. (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Aerospace Structures & Computational Mechanics); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","Continuous ultrasonic welding is a high-speed joining method for thermoplastic composites. Currently, a thin film energy director is used to focus the heat generation at the interface. However, areas of intact energy director remain in the welded seam, which significantly lowers the weld strength, and result in a non-uniformly welded seam. To improve the weld uniformity of continuous ultrasonically welded joints, we changed to a more compliant energy director. A woven polymer mesh energy director was found to give a significant improvement in weld quality. The mesh was flattened in between the composite adherends during the welding process. This flattening promoted a good contact between the energy director and the adherends, fully wetting the adherend surfaces, resulting in a more uniformly welded seam without areas of intact energy director.","continuous welded seam; Fusion bonding; high frequency welding; joining; polymer mesh","en","journal article","","","","","","","","","","","Aerospace Manufacturing Technologies","","",""
"uuid:be68fb95-335d-45d1-9a1e-b35098d6ab84","http://resolver.tudelft.nl/uuid:be68fb95-335d-45d1-9a1e-b35098d6ab84","Influence of geometrical parameters on the strength of Hybrid CFRP-aluminium tubular adhesive joints","Lavalette, N. (TU Delft Structural Integrity & Composites); Bergsma, O.K. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","Tubular adhesive joints, used in truss structures to join pultruded carbon fibre-reinforced polymer members to aluminium nodes, are modelled with varying dimensions. The numerical model uses a Cohesive Zone Modelling formulation with a trapezoidal traction-separation law for the adhesive layer, and experimental tests are carried to validate it. The results showed that the joint strength increases significantly with the bonding area, with a limit on the overlap length above which it stops increasing. This upper limit is affected by the thickness and tapering angle of the adherends, due to their influence on the shear stress distribution along the overlap. On the other hand, the adhesive thickness has only a marginal influence on the joint strength.","Adhesive joints; Cohesive zone modelling; Ductile adhesives; Hybrid joints; Mechanical testing; Tubular joints","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:e0a0eb51-7ee4-46cf-8e93-b05e010b314f","http://resolver.tudelft.nl/uuid:e0a0eb51-7ee4-46cf-8e93-b05e010b314f","Simulation of ultrasonic array inspection of composites with side drilled holes","Anand, C. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Shroff, S. (TU Delft Aerospace Structures & Computational Mechanics); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","In this paper we ultrasonic signals from array transducers are simulated using the Thompson and Gray measurement model. The measurement model consists of a beam model, a system efficiency factor which characterizes the response of the electro-mechanical and electrical components of the system, and a flaw scattering model. To inspect layered composite structures with complex geometries such as curvature, a beam model which is non-singular is required. Hence a multi Gaussian beam model for an ultrasonic array which includes the slowness surface parameters for unidirectional CFRP is investigated. The system functions of the ultrasonic array are modelled using a system efficiency model for a rectangular array. The Kirchoff approximation and separation of variables method for far field scattering in anisotropic materials is used to model the far field response of scatterers such as side drilled holes (SDH) in unidirectional CFRP. In summary the ultrasonic measurement model developed is able to predict the signals from scatterers such as side drilled holes (SDH) in transversely isotropic CFRP.","Composite; Phased array; Side drilled hole; Simulation; Ultrasonic","en","conference paper","Applied Mechanics Laboratory","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:e1be0a43-0785-48de-b069-ee45a64d3000","http://resolver.tudelft.nl/uuid:e1be0a43-0785-48de-b069-ee45a64d3000","Simulation of ultrasonic beam propagation from phased arrays in anisotropic media using linearly phased multi-Gaussian beams","Anand, C. (TU Delft Structural Integrity & Composites); Delrue, Steven (Katholieke Universiteit Leuven); Jeong, Hyunjo (Wonkwang University); Shroff, Sonell (Clean Sky 2); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","Phased array ultrasonic testing is widely used to test structures for flaws due to its ability to produce steered and focused beams. The inherent anisotropic nature of some materials, however, leads to skewing and distortion of the phased array beam and consequently measurement errors. To overcome this, a quantitative model of phased array beam propagation in such materials is required, so as to accurately model the skew and the distortion. The existing phased array beam models which are based on exact methods or numerical methods are computationally expensive or time consuming. This article proposes a modeling approach based on developing the linear phased multi-Gaussian beam (MGB) approach to model beam steering in anisotropic media. MGBs have the advantages of being computationally inexpensive and remaining non-singular. This article provides a comparison of the beam propagation modeled by the developed ordinary Gaussian beam and linear phased Gaussian beam models through transversely isotropic austenitic steel for different steering angles. It is shown that the linear phased Gaussian beam model outperforms the ordinary one, especially at steering angles higher than 20° in anisotropic solids. The proposed model allows us to model the beam propagation from phased arrays in both isotropic and anisotropic media in a way that is computationally inexpensive. As a further step, the developed model has been validated against a finite element model (FEM) computed using COMSOL Multiphysics.","Anisotropy; beam modeling; multi-Gaussian; ultrasonic transducer arrays; Phased arrays; Transducers; Computational modeling; Media; Acoustics; Numerical models; Acoustic beams","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2021-12-22","","","Structural Integrity & Composites","","",""
"uuid:aec12f37-886e-4122-8f02-343b9a0d9973","http://resolver.tudelft.nl/uuid:aec12f37-886e-4122-8f02-343b9a0d9973","Strategies for swift automated pick-and-place operations of multiple large-sized layers of reinforcement - a critical review","de Zeeuw, C.M. (TU Delft Structural Integrity & Composites); Peeters, D.M.J. (TU Delft Aerospace Manufacturing Technologies); Bergsma, O.K. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","For the application of composite materials to become more widespread and replace traditional materials their manufacturing processes and final products will need to be competitive and be e.g. lighter, stronger or stiffer and quicker, easier or more cost-efficient to produce than traditional materials. The state of the art for pick-and-place operations for the manufacturing of composite parts focuses on handling single lab-sized layers at undisclosed speeds. The process could however be more competitive by being able to handle more and larger layers in a faster manner than currently presented in research. The aim of the paper is to evaluate the existing pick-and-place strategies on their suitability for the swift automated handling of multiple large-sized layers of reinforcement. The review shows that many of the existing techniques could be suitable for different scenario’s and discusses which factors are to be taken into account when dealing with large layers, more than one layer or rapid handling. (Figure presented.).","automation; fabrics/textiles; gripping strategies; lay-up; Pick-and-place; ply handling strategies; review; up-scaling; OA-Fund TU Delft","en","review","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:830667d9-4b36-4c2f-849f-2e582b733042","http://resolver.tudelft.nl/uuid:830667d9-4b36-4c2f-849f-2e582b733042","Damage Diagnostics Utilizing Sensor Data Fusion","Broer, Agnes A.R. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","Experimental campaign to develop a multi-sensing structural health monitoring (SHM) framework in order to diagnose impact damage in stiffened composite aircraft structures on all four SHM levels, namely 1) detection, 2) localisation, 3) type, and 4) severity.","","en","poster","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:26f27611-e16f-446f-b18b-51818b905802","http://resolver.tudelft.nl/uuid:26f27611-e16f-446f-b18b-51818b905802","Integrative approach for transducer positioning optimization for ultrasonic structural health monitoring for the detection of deterministic and probabilistic damage location","Ewald, Vincentius (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","The concept of structural health monitoring has been introduced to ensure structural integrity during the design lifetime of a structure. The main objectives of structural health monitoring are to detect, locate, quantify, and predict any damage that occurs during this lifetime of the structure so that effective and efficient maintenance and repair procedures can be performed. The location of structural damage events can be discretized as deterministic and probabilistic. A deterministic location specifies that the damage occurs in high-stress regions or other regions that can be predicted by the structural design, such as the most probable location for a fatigue crack. A probabilistic damage event is one where the location of the damage is independent of structural design parameters, such as hail impact, bird strike, and impact from ground vehicles. A structural health monitoring system should be able to handle both these damage occurrences. In our previous work, we optimized the transducer placement in Lamb wave–based structural health monitoring for the detection of a fatigue crack that emerges from a rivet hole. In this article, we demonstrate a combination of that method with a different sensor placement optimization method to add the capability to detect probabilistic damage location. First, we considered the ultrasonic wave attenuation in the structure and based on this attenuation, we created a fitness function. Since this fitness function is difficult to solve due to its combinatorial nature, we compared three common metaheuristic stochastic strategies: global random search, greedy algorithm, and genetic algorithm, for solving this problem. The results of this analysis were then integrated with the previously described deterministic approach, making a global structural health monitoring sensor placement strategy that balances the need to detect both pre-determined and random damage location occurrences. The analytical result of the study presented is validated by experiment.","fatigue crack; genetic algorithm; greedy algorithm; impact damage; metaheuristic search; random search; sensor placement option; Ultrasonic structural health monitoring","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:1ea60959-7eaa-43fd-adff-5c39fa0034b5","http://resolver.tudelft.nl/uuid:1ea60959-7eaa-43fd-adff-5c39fa0034b5","Multi-modal fibre optic shape sensing for the SmartX morphing wing demonstrator (PPT)","Nazeer, N. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","PowerPoint presentation","","en","other","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:6e254861-090a-4796-a181-423b41dc7c23","http://resolver.tudelft.nl/uuid:6e254861-090a-4796-a181-423b41dc7c23","Ultrasonic welding of CF/epoxy to CF/PEEK composites: Effect of the energy director material on the welding process","Tsiangou, E. (TU Delft Aerospace Manufacturing Technologies); Teixeira De Freitas, S. (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Aerospace Manufacturing Technologies); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","With its short heating times, ultrasonic welding is a highly promising technique for joining thermoplastic (TPC) to thermoset (TSC) composites, to prevent thermal degradation of the thermoset adherend. A neat thermoplastic coupling layer is co-cured on the surface to be welded to make the TSC “weldable”. For welding CF/PEEK to a TSC adherend, it would be logical to use PEEK as the coupling layer. However PEEK and epoxy are not miscible with each other, therefore a bond created after co-curing of these two materials is not reliable. PEI on the other hand is known to be miscible to most epoxy systems at high temperatures and PEEK polymers, hence it is an excellent candidate for the coupling layer material. The other necessary element for ultrasonic welding is the energy director (ED), a neat TP film placed at the interface to help promote heat generation through preferential frictional and viscoelastic heating. Usually EDs are made from the same material as the TP matrix, but in this case ED can be either PEI or PEEK. Mechanical testing and fractographic analysis showed that the usage of a PEEK ED is the most successful approach. This research is part of the European project EFFICOMP.","Composites; Energy director; Thermoplastics; Thermosets; Ultrasonic welding","en","conference paper","Applied Mechanics Laboratory","","","","","","","","","","Aerospace Manufacturing Technologies","","",""
"uuid:a3fcdad0-1f0d-46ee-99d9-475a5005e98d","http://resolver.tudelft.nl/uuid:a3fcdad0-1f0d-46ee-99d9-475a5005e98d","Multi-spot ultrasonic welding of thermoplastic composite single-lap joints: Effect of spot spacing and number of spots on weld strength","Zhao, T. (TU Delft Structural Integrity & Composites); Tsakoniatis, Ioannis (TU Delft Aerospace Manufacturing Technologies); Rans, C.D. (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Aerospace Manufacturing Technologies); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","Thermoplastic composite spot welded joints are more well-suited for carrying shear load rather than peel load. However, peel load is difficult to be eliminated in single-lap joint configuration. In this paper, a series of mechanical tests were carried out to study the effects of the spot spacing and the number of welded spots on the secondary bending and subsequently on the strength of the multi-spot welded joints. Based on that, a comparative study was performed on the load-carrying capability of multi-spot welded and mechanically fastened joints assembled with multi-row fasteners. It was found that, by increasing the spot spacing and the number of welded spots, the secondary bending of the multi-spot welded joints can be effectively decreased, which eventually results in a comparable load-carrying capability with respect to the mechanically fastened joints.","Mechanical behaviour; Secondary bending; Spot welded joint; Thermoplastic composites","en","conference paper","Applied Mechanics Laboratory","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:9a5a47e9-1e34-49ca-9106-962b7d8e17bd","http://resolver.tudelft.nl/uuid:9a5a47e9-1e34-49ca-9106-962b7d8e17bd","Effect of ultrasonic welding process on the crystallinity at the welding interface of CF/PPS joints","Koutras, N. (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Aerospace Manufacturing Technologies); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","The influence of the ultrasonic welding process parameters, namely the force and the vibration amplitude, on the crystallinity degree at the welding interface of CF/PPS (carbon fibre reinforced poly(phenylene) sulphide) joints is investigated. Two different sets of parameters, one representing high force and high vibration amplitude (1000 N, 86.2 μm) and one representing low force and low vibration amplitude (300 N, 51.8 μm), were used in this study. The temperature at the centre of the overlap was measured using K-type thermocouples in order to obtain the cooling rate for each set of parameters. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements were performed in order to determine the crystallinity degree of PPS at the welding interface. It was found that a force of 300 N and a vibration amplitude of 51.8 μm could obtain a PPS of a moderate crystallinity degree (14.6%) and an average PPS crystallite size of 41.3 Å, showing that it is possible to obtain a semi-crystalline welding interface by appropriately modifying the process parameters.","Crystallinity; DSC; PPS; Thermoplastic Composites; Ultrasonic Welding","en","conference paper","Applied Mechanics Laboratory","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:6ac44401-2c02-4550-a38c-f117bd925017","http://resolver.tudelft.nl/uuid:6ac44401-2c02-4550-a38c-f117bd925017","Light scattering and rheological effects in an optical fibre coupled nanoparticle suspension","Wang, X. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites)","Berghmans, Francis (editor); Mignani, Anna G. (editor)","2020","This study forms the first part of research into enhancing the forward and back scattering of light in an optical fibre using nanoparticles (NPs). This approach has the potential to enhance the sensitivity of optical fibre sensing by increasing the signal-to-noise ratio. The work described in this paper is focused on understanding the scattering of light by a suspension of NPs in refractive index matching liquid. It was noted early in the experimental work that rheological effects related to the viscosity and flow of the liquid affect the scattered light measured and therefore these effects are considered in the analysis. Gold nanoparticles in the tens to hundreds of micrometre size range were selected as the scattering particles based on their optical properties. These are suspended in a refractive index liquid with a similar refractive index to the optical fibre core. Effort was needed to transfer the NPs from their aqueous sodium citrate solution to the paraffin based solution. We investigated two types of interaction with the optical fibre: (i) dropping the NP suspension onto the end of a single-mode optical fibre and (ii) using the NP suspension as an interface between two single-mode optical fibres. It was noted that the surface tension of the liquid, the diameter of the fibre and the spacing between the fibres in case (ii) influence the reflected and transmitted light. In case of excess liquid, droplets flowed down the fibre and interestingly in case (ii) modified the reflected and forward transmitted light as it passed across the fibre interface. Our initial findings are that the influence of the gap between two optical fibres decreased after dropping refractive index liquid into the gap after fibre collimation, which is a beneficial result for understanding the influence of scattered light from a liquid containing NPs. Note, the position between the two fibres can also change due to the weight of the droplet and the fibre ends had to be re-collimated to investigate the influence of the moving droplets. These results will be expanded by additional experiments and modelling of the scattering from the nanoparticales and droplets.","Light scattering; Nanoparticle; Optical fibre; Rheological effect","en","conference paper","SPIE","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:d1315567-38c0-429b-adb2-5defa65ff87c","http://resolver.tudelft.nl/uuid:d1315567-38c0-429b-adb2-5defa65ff87c","Prediction models for distortions and residual stresses in thermoset polymer laminates: An overview","Abouhamzeh, M. (TU Delft Structural Integrity & Composites); Sinke, J. (TU Delft Aerospace Manufacturing Technologies); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2019","This paper reviews predictive models developed for the development of residual stresses and shape distortions during the manufacturing of thermoset polymeric/composite materials. Different sources that produce residual stresses and shape changes in the laminated panels are described and reviewed. An overview is presented on the characterisation and predictions of the phenomena resulting in residual stresses. The focus will be on the models accounting for the parameters during the cure cycle of the thermoset composite materials published in the literature from 2005 until 2018. The material types covered here range from thermoset adhesives, full composites, and fibre metal laminates. Furthermore, selected works are reviewed on the reduction of the shape changes and residual stresses of composites and fibre metal laminates consisting of thermoset polymers.","Adhesive; Composite; Cure cycle; Distortions; Hybrid; Model; Residual stresses; Thermoset","en","review","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:564893ac-34ce-41fd-be1b-5f587e9717a2","http://resolver.tudelft.nl/uuid:564893ac-34ce-41fd-be1b-5f587e9717a2","Simultaneous position and displacement sensing using two fibre Bragg grating sensors","Nazeer, N. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","Lynch, Jerome P. (editor); Sohn, Hoon (editor); Wang, Kon-Well (editor); Huang, Haiying (editor)","2019","Over the years, many shape sensing methods have been developed with technologies including optical fibre, PZT and fringe projection. Among them, optical fibres have gained a lot of attention due to their unobtrusive nature when either surface mounted or embedded in the structure. Optical fibre Bragg gratings (FBG) are currently employed for structural health monitoring in civil and aerospace systems and their shape sensing capabilities have been previously reported. In this paper, we propose a novel fibre optic based shape sensor of an isotropic cantilever beam based on the principles of interferometry and FBG sensing. The method described in this paper uses a standard single core single-mode optical fibre and the least number of sensors to estimate the shape, making it comparatively an inexpensive sensing method. On displacing the beam with an unknown magnitude and at an unknown location along the beam, we are able to demonstrate that we can measure the shape of the displaced beam and the magnitude and location of the force applied. The analysis involves using a calibration method and an iterative calculation to measure the two unknowns. An analytical model based on the known beam theories was used to assess the accuracy of the measurements. The preliminary analysis yielded an accuracy of ±1 mm and ±50 mm for the displacement and location, respectively.","Fibre Bragg grating; Optical interferometry; Shape sensing; Strain measurement; Structural health monitoring","en","conference paper","SPIE","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:64358950-7297-4759-99f3-33a8c57b0095","http://resolver.tudelft.nl/uuid:64358950-7297-4759-99f3-33a8c57b0095","Real time diagnostics and prognostics of UAV lithium-polymer batteries","Eleftheroglou, N. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites); Loutas, Theodoros (University of Patras); Mansouri, Sina Sharif (Luleå Univ. of Technology); Georgoulas, George (University of Patras); Karvelis, Petros (Luleå Univ. of Technology); Nikolakopoulos, George (Luleå Univ. of Technology); Benedictus, R. (TU Delft Structural Integrity & Composites)","Scott Clements, N. (editor)","2019","This paper examines diagnostics and prognostics of Lithium-Polymer (Li-Po) batteries for unmanned aerial vehicles (UAVs). Several discharge voltage histories obtained during actual indoor flights constitute the training data for a data-driven approach, utilizing the Non-Homogenous Hidden Semi Markov model (NHHSMM). NHHSMM is a suitable candidate as it has a rich mathematical structure, which is capable of describing the discharge process of Li-Po batteries and providing diagnostic and prognostic measures. Diagnostics and prognostics in unseen data are obtained and compared with the actual remaining flight time in order to validate the effectiveness of the selected model.","","en","conference paper","PHM Society","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:56ea1fdb-45f2-4c36-80a8-101e8437fb7c","http://resolver.tudelft.nl/uuid:56ea1fdb-45f2-4c36-80a8-101e8437fb7c","Extreme prognostics for remaining useful life analysis of composite structures","Eleftheroglou, N. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","Scott Clements, N. (editor)","2019","The procedure of fatigue damage accumulation in composite structures is still unknown and depends on several parameters such as type and frequency of loading, stacking sequence and material properties. Additionally, the nonhomogeneous and anisotropic nature of composites result to a stochastic activation of the different failure mechanisms and make the estimation of remaining useful life (RUL) very complex but interesting task. Data driven probabilistic methodologies have found increasing use the last decade and provide a platform for reliable estimations of RUL utilizing condition monitoring (CM) data. However, the fatigue life of a specific composite structure has a quite significant scatter, with specimens that either underperform or outperform. These specimens are often referred as outliers and the estimation of their RUL is challenging. This study proposes a new RUL probabilistic model, the Extreme Non-Homogenous Hidden Semi Markov Model (ENHHSMM) which is an extension of the Non-Homogenous Hidden Semi Markov Model (NHHSMM). The ENHHSMM uses dynamic diagnostic measures, which are estimated based on the training and testing CM data and adapts dynamically the trained parameters of the NHHSMM. The available CM data are acoustic emission data recorded throughout fatigue testing of open-hole carbon–epoxy specimens. RUL estimations from the ENHHSMM and NHHSMM are compared. The ENHHSMM is concluded as the preferable option since it provides more accurate outlier prognostics.","","en","conference paper","PHM Society","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:9af3be74-655e-4125-bb6e-c8e54622a4fd","http://resolver.tudelft.nl/uuid:9af3be74-655e-4125-bb6e-c8e54622a4fd","On the influence of overlap topology on tensile strength of composite bonded joints: A multistacking design","Kupski, J.A. (TU Delft Structural Integrity & Composites); Teixeira De Freitas, S. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2019","The goal of this study is to investigate new designs of composite bonded joints in order to improve their strength under tensile loading. Multiple stacked overlaps are compared with single overlap designs. The concept of multiple stacking is well known as ply-interleaving technique for co-curing dissimilar materials. For a secondary bonding process, a similar concept is used in tongue-and-groove joints. However, it is so far limited to one stacking level due to the complexity of the design. By means of thin unidirectional layers, the tongue-and-groove design is expanded further to two stacking sequences and applied to secondary bonding of CFRP adherends. Single lap joints of 12.7 and 25.4 mm overlap length were compared to finger joints with 1 and 2 overlaps of 12.7 mm overlap length, stacked through the thickness. Specimens were tested according to ASTM D-5868-01. The initial and final failure load were recorded. The study shows that for the same overlap length in a multi-stacked configuration, there is a potential for higher average lap strength, in comparison with an increase in overlap length of a single overlap. This effect might be mainly due to the reduction of secondary bending moment and by load distribution over multiple interfaces.","Adhesive bonding; Composite joints; Finger joints; Joint topology","en","conference paper","Applied Mechanics Laboratory","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:90a48075-df46-4829-aeb5-4b47b39464bf","http://resolver.tudelft.nl/uuid:90a48075-df46-4829-aeb5-4b47b39464bf","A large displacement orthotropic viscoelastic model for manufacturing-induced distortions in Fibre Metal Laminates","Abouhamzeh, M. (TU Delft Structural Integrity & Composites); Sinke, J. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials; TU Delft Structural Integrity & Composites)","","2019","Distortions and residual stresses are predicted in Fibre Metal Laminates (FMLs) under large deformations. A new modelling procedure is presented for small and large deformation analysis of thermo-viscoelastic problems of orthotropic materials. The material model is implemented in a finite element package which can be used for cure and/or temperature dependent response of composites undergoing large rotations but with small strains.Temperature-dependent and viscoelastic responses are characterised for GLARE, as the mostly used type of FMLs. The geometrically nonlinear thermo-viscoelastic model is used to predict the manufacturing-induced warpage of panels. The curing stresses are calculated from a previously developed model accounting for chemical shrinkage and stiffness evolution of the prepreg layers during cure. The shape deviation of some non-symmetric GLARE panels are predicted and compared to the real measurement of fabricated laminates. The accuracy of the model is verified which can be used in further studies to improve the precision of manufacturing and assembly and also to have better prediction of the fatigue life and residual strength.","Curing; GLARE; Glass-epoxy prepreg; Large-deformation; Thermo-viscoelastic","en","journal article","","","","","","","","2020-01-01","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:4dbedb7d-fb0e-4d7d-9fc2-b003529bee2e","http://resolver.tudelft.nl/uuid:4dbedb7d-fb0e-4d7d-9fc2-b003529bee2e","Composite layup effect on the failure mechanism of single lap bonded joints","Kupski, J.A. (TU Delft Structural Integrity & Composites); Teixeira De Freitas, S. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites); Camanho, P. P. (Universidade do Porto; INEGI); Benedictus, R. (TU Delft Aerospace Structures & Materials)","","2019","Single lap bonded joints with four different composite adherend stacking sequences were tested and numerically simulated. The aim was to evaluate the effect of the layups on the quasi-static tensile failure of the bonded joints. The study shows that increasing the adherends bending stiffness postpones the damage initiation in the joint. However, this is no longer valid for final failure. The ultimate load is influenced by how the damage progresses. For similar bending stiffness, a layup that leads to the crack propagating from the adhesive towards the inside layers of the composite increases the ultimate load. The failure mode is highly influenced by the orientation of the interface lamina in contact with the adhesive, such that, a 0° interface ply causes failure within the bond line, while a 90° interface ply causes failure inside the composite adherend. Finally, it is concluded that a quasi-isotropic layup may not be the best choice in terms of tensile joint strength. In order to improve tensile strength up to damage initiation, the layup should be optimized for bending stiffness, while up to final failure, a stacking sequence that yields to a complex crack path inside the composite can lead to higher ultimate loads.","Composite bonded joints; Composite layup variation; Single lap joints","en","journal article","","","","","","","","","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:980bd084-e5a7-47b5-8222-6dde031fd96a","http://resolver.tudelft.nl/uuid:980bd084-e5a7-47b5-8222-6dde031fd96a","Diagnostic of manufacturing defects in ultrasonically welded thermoplastic composite joints using ultrasonic guided waves","Ochôa, Pedro (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Aerospace Manufacturing Technologies); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2019","This article presents research about the propagation of ultrasonic guided waves in ultrasonically welded thermoplastic composite joints. The goal of the study was to understand the effect of weld manufacturing defects on guided wave transmission across the joint. Triangular energy-directors integrated into the lower composite adherends enabled the production of defective joints in a controlled manner. The produced defect types were unwelded areas and adherend fibre bundle distortion. The reference condition corresponded to the fully welded stage which showed the highest single-lap shear strength. It was possible to detect adherend fibre bundle distortion through the increase in the negative shift of the signal characteristic frequency. Evidence of the presence of unwelded areas was found in the increase of Time-of-Flight of the maximum amplitude Lamb wave group. The sensitivity of the diagnostic parameters was found to be dependent on the ultrasonic guided wave excitation frequency.","Manufacturing defects; Structural health monitoring; Thermoplastic composite; Ultrasonic guided waves; Ultrasonic welding","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2021-12-22","","","Structural Integrity & Composites","","",""
"uuid:1d0c3e80-2861-4912-ae89-3f916efbdb44","http://resolver.tudelft.nl/uuid:1d0c3e80-2861-4912-ae89-3f916efbdb44","Investigation on the melting of the weld interface in continuous ultrasonic welding of thermoplastic composites","Jongbloed, B.C.P. (TU Delft Aerospace Manufacturing Technologies); Teuwen, Julie J.E. (TU Delft Aerospace Manufacturing Technologies); Villegas, I.F. (TU Delft Aerospace Structures & Computational Mechanics); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2019","Continuous ultrasonic welding is a new promising high-speed joining technique for thermoplastic composites. At the moment no straightforward method exists to find an optimum welding speed to easily obtain high strength joints. However, for static ultrasonic welding a systematic approach is available. Therefore, the aim of this study is to understand whether the optimum welding time in static ultrasonic welding can be related to the welding speed in continuous ultrasonic welding. The duration of the welding stages in static and continuous welding were compared in order to find similarities and discrepancies. The duration of the welding stages in continuous ultrasonic welding was estimated by analysing the weld interface and measuring the distances of the stages in the fractured interface around the location where the weld was stopped. No significant difference in weld duration was found for the first welding stage in which the mesh energy director is flattened. However, the second stage in which the energy director and adherends melt simultaneously, lasted much longer for the continuous welding process. This was possibly caused by the more constraining boundary conditions in the continuous welding process. In conclusion, the optimum welding speed in continuous welding was lower than the expected optimum welding speed based on the optimum welding time in static ultrasonic welding, because the second welding stage lasted longer in the continuous ultrasonic welding process.","","en","conference paper","","","","","","","","","","","Aerospace Manufacturing Technologies","","",""
"uuid:efd63210-7d9c-4e18-848c-7f9382f603c0","http://resolver.tudelft.nl/uuid:efd63210-7d9c-4e18-848c-7f9382f603c0","From thin to extra-thick adhesive layer thicknesses: Fracture of bonded joints under mode I loading conditions","Lopes Fernandes, R. (TU Delft Structural Integrity & Composites); Teixeira De Freitas, S. (TU Delft Structural Integrity & Composites); Budzik, Michal K.; Poulis, J.A. (TU Delft Adhesion Institute); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2019","The fracture behaviour of joints bonded with a structural epoxy adhesive and bond line thicknesses of 0.1–4.5 mm has been studied. However, limited research is found on similar joints with thicker bond lines, which are relevant for maritime applications. Therefore, the effect of the adhesive bond line thickness, varying from 0.4 to 10.1 mm, on the mode I fracture behaviour of steel to steel joints bonded with a structural epoxy adhesive was investigated in this study. An experimental test campaign of double-cantilever beam (DCB) specimens was carried out in laboratory conditions. Five bond line thicknesses were studied: 0.4, 1.1, 2.6, 4.1 and 10.1 mm. Analytical predictions of the experimental load-displacement curves were performed based on the Simple Beam Theory (SBT), the Compliance Calibration Method (CCM) and the Penado-Kanninen (P-K) model. The P-K model was used to determine the mode I strain energy release rate (SERR). The average mode I SERR, G Iav., presented similar values for the specimens with adhesive bond line thicknesses of 0.4, 1.1 and 2.6 mm (G I av.=0.71, 0.61, 0.63 N/mm, respectively). However, it increased by approximately 63% for 4.1 mm (G I av.=1.16 N/mm) and decreased by about 10% (in comparison with 4.1 mm) for the 10.1 mm (G I av.=1.04 N/mm). The trend of the G Iav. in relation to the bond line thickness is explained by the combination of three factors: the crack path location, the failure surfaces features and the stress field ahead of the crack tip.","Extra-thick bond lines; Fracture process zone; Fracture toughness; Mode I","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2022-08-09","","","Structural Integrity & Composites","","",""
"uuid:335c77f8-b455-4d76-801b-f99a98156ada","http://resolver.tudelft.nl/uuid:335c77f8-b455-4d76-801b-f99a98156ada","Evaluation of the mechanical performance of a composite multi-cell tank for cryogenic storage: Part II – Experimental assessment","Tapeinos, I. (TU Delft Aerospace Manufacturing Technologies); Rajabzadeh, Aydin (TU Delft Signal Processing Systems); Zarouchas, D. (TU Delft Structural Integrity & Composites); Stief, Malte (Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR)); Groves, R.M. (TU Delft Structural Integrity & Composites); Koussios, S. (TU Delft Aerospace Manufacturing Technologies); Benedictus, R. (TU Delft Aerospace Structures & Materials)","","2019","This study focuses on the understanding of the thermal and structural behavior of an innovative Type IV multi-spherical composite-overwrapped pressure vessel through an experimental assessment that consists of hydrostatic testing at ambient conditions and pressure cycling with a cryogenic medium (LN2). During hydro-burst testing at a high displacement rate, the strain and damage progression is monitored with Digital-Image-Correlation (DIC) and Acoustic Emission (AE) techniques respectively. The effect of filling with LN2, pressure cycling and draining on the composite overwrap temperature gradient and strain evolution is additionally obtained with Fiber Bragg Gratings (FBGs) and thermocouples. Utilization of AE helped to reveal the different damage mechanisms occurring and enabled the evaluation of the pressure window of the multi-sphere. The experimental measurements in the cryogenic regime verified the suitability of the involved stiffness and coefficient of thermal expansion (CTE) fitting functions developed in [32] that enable to establish of a relationship between strain and temperature during cryogenic chill-down and pressure cycling. This study provides a framework about the suitability of conformal Type IV multi-spherical COPVs for cryogenic storage.","Cryo-cycling; Damage progression; Hydrostatic burst; Multi-cell tank; Strain monitoring","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2021-12-22","","Aerospace Structures & Materials","Aerospace Manufacturing Technologies","","",""
"uuid:7246321e-d09e-4ebe-b7e8-831927bec6a8","http://resolver.tudelft.nl/uuid:7246321e-d09e-4ebe-b7e8-831927bec6a8","Systematic multiparameter design methodology for an ultrasonic health monitoring system for full-scale composite aircraft primary structures","Ochôa, Pedro (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials)","","2019","The successful utilization of guided wave-based structural health monitoring (SHM) for detailed quantitative diagnostic of damage in composite aircraft primary structures depends on the excitation frequency, geometry, and positioning of the piezoelectric transducers. This study proposes a novel methodology to consistently define those parameters, which is not tuned for a single damage size, does not resort to unrealistic usage of pure guided wave modes, and is applicable to a generic full-scale composite aircraft primary structure. The proposed criteria for designing the piezoelectric transducer network are based on sensor output, coupled electro-mechanical response of the transducer-structure assembly, energy transfer from the bonded piezoelectric transducer to the structure, wavefront coverage of the monitored area, and measurement equipment capabilities. The design methodology was successfully validated by testing the capabilities of the SHM system for the diagnostic of barely visible impact damage of different severities, applied in different locations on a full-scale thermoplastic composite aircraft stiffened panel.","composite aircraft primary structure; experimental validation; structural health monitoring; system design; ultrasonic guided wave","en","journal article","","","","","","","","","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:5685c1c7-a2f9-4f2e-8525-9578a1773d7d","http://resolver.tudelft.nl/uuid:5685c1c7-a2f9-4f2e-8525-9578a1773d7d","Determining finite-width-correction factors for fatigue crack growth prediction in GLARE using the equivalent compliance method","Zhao, Yuan (Harbin Institute of Technology); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Wu, Zengwen (Harbin Institute of Technology); Zhou, Zhengong (Harbin Institute of Technology); Fang, Guodong (Harbin Institute of Technology); Zhang, Jiazhen (Harbin Institute of Technology); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2019","Finite-width-correction factors (FWCF) are required for GLARE to accurately predict fatigue crack growth using linear elastic fracture mechanics. As demonstrated in earlier work, these factors effectively correct for the change in specimen compliance, which in GLARE relates to intact fibre layers and the formation of delaminations between these layers and the cracked metal layers. Therefore, the development of delaminations in various GLARE grades were studied using digital image correlation during fatigue crack growth experiments under different maximum stresses and stress ratios. The elongation of GLARE in loading direction was recorded by crosshead displacement during fatigue testing, and was correlated to the observed development of the delamination area. The relationship between effective delamination area and effective GLARE specimen compliance is used as basis for determining explicit formulations for the FWCF for GLARE.","Applied work; Compliance; Delamination; Finite-width-correction factor; GLARE","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2019-06-01","","","Structural Integrity & Composites","","",""
"uuid:0ca117b3-6ee4-4267-a581-984fc108d37a","http://resolver.tudelft.nl/uuid:0ca117b3-6ee4-4267-a581-984fc108d37a","DeepSHM: A deep learning approach for structural health monitoring based on guided Lamb wave technique","Ewald, Vincentius (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","Lynch, Jerome P. (editor); Sohn, Hoon (editor); Wang, Kon-Well (editor); Huang, Haiying (editor)","2019","In our previous work, we demonstrated how to use inductive bias to infuse a convolutional neural network (CNN) with domain knowledge from fatigue analysis for aircraft visual NDE. We extend this concept to SHM and therefore in this paper, we present a novel framework called DeepSHM which involves data augmentation of captured sensor signals and formalizes a generic method for end-to-end deep learning for SHM. The study case is limited to ultrasonic guided waves SHM. The sensor signal response from a Finite-Element-Model (FEM) is pre-processed through wavelet transform to obtain the wavelet coefficient matrix (WCM), which is then fed into the CNN to be trained to obtain the neural weights. In this paper, we present the results of our investigation on CNN complexities that is needed to model the sensor signals based on simulation and experimental testing within the framework of DeepSHM concept.","convolutional neural network (CNN); damage classification; deep learning; Finite-Element-Modelling (FEM); guided Lamb wave; signal processing; Structural Health Monitoring (SHM)","en","conference paper","SPIE","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:f1fba7c4-0342-4daa-b835-16197761c259","http://resolver.tudelft.nl/uuid:f1fba7c4-0342-4daa-b835-16197761c259","On the physics of applying finite width and geometry correction factors in fatigue crack growth predictions of GLARE","Zhao, Y. (TU Delft Structural Integrity & Composites; Harbin Institute of Technology); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Zhou, Zhengong (Harbin Institute of Technology); Fang, Guodong (Harbin Institute of Technology); Zhang, Jiazhen (Harbin Institute of Technology); Benedictus, R. (TU Delft Aerospace Structures & Materials; TU Delft Structural Integrity & Composites)","","2018","In general, a finite width correction to stress intensity factor (SIF) is required in the fatigue crack growth. The finite width correction factor can be explained physically from the energy point of view. It is assumed that the finite width correction factor primarily constitutes an energy correction factor, i.e. it corrects the applied load for the work applied. To evaluate the finite width correction for FMLs, constant amplitude load fatigue crack growth tests were performed on monolithic aluminium 2024-T3 and the Fibre Metal Laminate GLARE containing 2024-T3 aluminium layers. The loads and displacements were recorded to quantify the total amount of work applied throughout each fatigue test. The crack length and delamination size were monitored by using digital image correlation technique to evaluate the dissipative energy. It appears that the Feddersen's and all other standard finite width correction significantly overestimates the effect for FMLs. The finite width correction to SIF for FMLs is small but cannot be neglected, and it is also greatly related to the Glare grades, stress ratio and stress level.","Energy; Fatigue; Fibre metal laminates; Finite width correction; Stress intensity factor","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2019-03-01","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:97cdd347-1fb6-45af-9d7a-6e08ce6cca9c","http://resolver.tudelft.nl/uuid:97cdd347-1fb6-45af-9d7a-6e08ce6cca9c","Structural health monitoring data fusion for in-situ life prognosis of composite structures","Eleftheroglou, N. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites); Loutas, Theodoros (University of Patras); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials; TU Delft Structural Integrity & Composites)","","2018","A novel framework to fuse structural health monitoring (SHM) data from different in-situ monitoring techniques is proposed aiming to develop a hyper-feature towards more effective prognostics. A state-of-the-art Non-Homogenous Hidden Semi Markov Model (NHHSMM) is utilized to model the damage accumulation of composite structures, subjected to fatigue loading, and estimate the remaining useful life (RUL) using conventional as well as fused SHM data. Acoustic Emission (AE) and Digital Image Correlation (DIC) are the selected in-situ SHM techniques. The proposed methodology is applied to open hole carbon/epoxy specimens under fatigue loading. RUL estimations utilizing features extracted from each SHM technique and after data fusion are compared, via established and newly proposed prognostic performance metrics.","Composite structures; Data fusion; Prognostic performance metrics; Remaining useful life; Structural health monitoring","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2018-12-01","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:91bb0697-d599-44a2-801d-64fdcaab63d9","http://resolver.tudelft.nl/uuid:91bb0697-d599-44a2-801d-64fdcaab63d9","A Roadmap for developing an Industrial Continuous Ultrasonic Welding Process for Thermoplastic Composites","Köhler, F. (Composite Technology Center (CTC) in Stade); Jongbloed, B.C.P. (TU Delft Aerospace Manufacturing Technologies); Morgado Martins Filipe, T.M. (TU Delft Aerospace Manufacturing Technologies); Herrmann, Axel (Composite Technology Center (CTC) in Stade); Villegas, I.F. (TU Delft Aerospace Structures & Computational Mechanics); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2018","The increasing use of fibre-reinforced plastics in the aerospace industry leads to challenges in joining these materials. The traditionally used mechanical fasteners introduce damage when used in composites by disrupting the fibres. However, thermoplastic composites allow for fusion bonding processes to join parts. Ultrasonic welding has shown to be a very promising high-speed fusion-bonding technique for thermoplastic composites. At the moment, a thorough understanding of the process is required to upscale the process for industrial usage. This study focuses on defining a roadmap to develop continuous ultrasonic welding to an industrially applicable level by presenting the current state of the art, ongoing developments, requirements, and challenges.","","en","conference paper","","","","","","","","","","","Aerospace Manufacturing Technologies","","",""
"uuid:855bd3ac-ab7c-4d81-b2b5-3be74b0c7093","http://resolver.tudelft.nl/uuid:855bd3ac-ab7c-4d81-b2b5-3be74b0c7093","Theoretical analysis of fatigue failure in mechanically fastened Fibre Metal Laminate joints containing multiple cracks","Wang, W. (TU Delft Structural Integrity & Composites); Rans, C.D. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials; TU Delft Structural Integrity & Composites)","","2018","Mechanically fastened joints are susceptible to the presence of multiple-site damage (MSD) cracks in the critical fastener row. Different from the MSD growth in joints consisting of metallic substrates, the two coupled metal crack growth and interfacial delamination propagation failure mechanisms in Fibre Metal Laminates (FMLs) make the prediction of fatigue behaviour in FML joints with MSD scenario burdensome and impractical when considering all factors influencing the fatigue performance. This paper presents a theoretical study on the MSD crack growth behaviour in mechanically fastened FML joints with a focus of modelling the effects of bearing and bypass loads. The proposed model in this paper is built upon analytical models dealing with MSD growth in flat FML panels and single crack growth in FML panels subjected to a combined tension-pin loading case. This model would be particularly useful for symmetric FML joints where no secondary bending effects present. A deliberately designed symmetric FML joint was tested to validate the proposed model. The model captures the rapid crack growth in the vicinity of fastener holes due to bearing stresses and crack acceleration due to the interaction of cracks. It is identified that the load redistribution between intact fastener rows and the cracked fastener row accelerates crack growth with crack length. The effects of secondary bending stresses in FML joints on the crack growth behaviour is extensively discussed. The performance of the proposed model for single lap FML joints is also examined using test data from open literature. It is found that the proposed model provides a conservative prediction for the tested single shear lap FML joint from open literature.","Crack growth acceleration; Fibre Metal Laminates; Load redistribution mechanism; Mechanically fastened joints; MSD","en","journal article","","","","","","","","2020-04-30","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:d8991858-e4f7-4aca-930a-8644ee8c1046","http://resolver.tudelft.nl/uuid:d8991858-e4f7-4aca-930a-8644ee8c1046","Design and Experimental Assessment of a Multi-spherical Composite- Overwrapped Pressure Vessel for Cryogenic Storage","Tapeinos, I. (TU Delft Aerospace Manufacturing Technologies); Rajabzadeh, Aydin (TU Delft Signal Processing Systems); Zarouchas, D. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Koussios, S. (TU Delft Aerospace Manufacturing Technologies); Benedictus, R. (TU Delft Aerospace Structures & Materials; TU Delft Structural Integrity & Composites)","Kostopoulos, Vassilis (editor)","2018","In the field of cryogenic storage, the medium inside the pressure vessel is in a liquid state and thus is incompressible. Therefore the storage tank should be designed in a way, that makes the best possible use of the available space within an aircraft. A composite-overwrapped pressure vessel (COPV) based on intersecting spheres (multi-sphere) provides a volumetrically efficient solution and leads to weight savings, due to reduced hoop stresses and less required thermal insulation. The latter is the result of the minimization of passive heat in the cryogenic liquid, associated with the fact that spheres have the minimum surface area for a given volume. In the present work, a numerical and experimental study of a novel multi-spherical COPV with a plastic liner was performed. A thermo-mechanical model based on Finite Element Analysis (FEA) was developed to assess the effect of cryogenic operation at the structure. The model incorporated the dependency of engineering properties and coefficient of thermal expansion of the composite overwrap and liner materials to temperature, in order to describe the structural response to cryogenic temperatures more accurately. This dependency was determined through using approximation functions based on results from material coupon testing. The temperature profile and strain response of the tank were assessed through thermocouples and Fiber Bragg Gratings (FBGs) respectively throughout the cryogenic chill-down and pressure cycling test. The experimental results verified the accuracy of the involved stiffness and CTE functions and the FE analysis with average offset of 10 [%]. The most important outcome from the study is the absence of damage in the composite overwrap after cryonic chill-down and pressure cycling, which can be regarded as positive indication of the suitability of Type IV multi-spherical COPVs for cryogenic storage applications.","","en","conference paper","","","","","","","","","","Aerospace Structures & Materials","Aerospace Manufacturing Technologies","","",""
"uuid:5c580a1c-986b-475f-9e90-5013684cab1d","http://resolver.tudelft.nl/uuid:5c580a1c-986b-475f-9e90-5013684cab1d","Towards robust sequential ultrasonic spot welding of thermoplastic composites: Welding process control strategy for consistent weld quality","Zhao, T. (TU Delft Structural Integrity & Composites); Broek, C.A. (TU Delft Education AE); Palardy, G. (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials; TU Delft Structural Integrity & Composites)","","2018","The research in this paper is an essential part of a bigger effort on developing robust sequential ultrasonic welding of multi-spot welded joints in thermoplastic composites. It mainly focused on assessing the impact of the changes in boundary conditions on the welding process and whether it could be circumvented by using an appropriate process control strategy. A two-step approach was followed by investigating: (1) the effect of boundary conditions on displacement- and energy-controlled single-spot welded joints and (2) displacement- and energy-controlled sequential ultrasonic welding of double-spot welded joints. The results showed that previous spots indeed affect the energy required to obtain an optimum new welded spot, which challenges the use of energy-controlled welding for this application. Contrarily, displacement-controlled welding was shown to provide consistent-quality welds with a constant set of welding parameters and it was hence identified as the most promising welding strategy for sequential ultrasonic welding of thermoplastic composites.","Fractography; Joints/joining; Mechanical properties; Thermoplastic resin","en","journal article","","","","","","","","2020-03-23","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:d61a208f-282e-4726-94ee-c240df9b969e","http://resolver.tudelft.nl/uuid:d61a208f-282e-4726-94ee-c240df9b969e","The stress ratio effect on plastic dissipation during fatigue crack growth","Quan, H. (TU Delft Structural Integrity & Composites); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials; TU Delft Structural Integrity & Composites)","","2018","Plastic energy dissipation is inevitable during fatigue crack growth. There have been previous attempts reported in literature to correlate the plastic dissipated energy (dW/dN) to fatigue crack growth rate (da/dN). However, at a given dW/dN, the da/dN changes with the ratio of minimum and maximum loads, known as the stress ratio. This paper describes an experimental study carried out on 2024-T3 central crack tension specimens to quantify the relation between dW/dN and da/dN. By selecting different stress ratios in the individual tests, the experiments reveal the influence of the stress ratio on this relationship. It is evident that dW/dN has no unique relationship with da/dN valid for the tested stress ratios. Instead, the relationship for each stress ratio is different. This is illustrated with the value of plastic dissipation per unit of fatigue crack growth (dW/da), representing the effective resistance to the crack increment. This value is not a constant, but changes with the stress ratios and da/dN values. Hence the plastic energy dissipation cannot be used directly for predicting crack growth.","","en","journal article","","","","","","","","","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:f3386955-628d-4131-b3d0-37613a47879f","http://resolver.tudelft.nl/uuid:f3386955-628d-4131-b3d0-37613a47879f","Fatigue crack surface area and crack front length: New ways to look at fatigue crack growth","van Kuijk, J.J.A. (TU Delft Structural Integrity & Composites); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials; TU Delft Structural Integrity & Composites)","","2018","This paper discusses the appropriateness of crack length as a reference dimension for fatigue damage. Current discussion on short crack versus long crack data is still divided between various approaches to model small crack growth. A proper physical explanation of the probable cause of the apparent differences between short crack and long crack data is not yet provided. Long crack data often comprises crack growth in constant thickness specimens, with a through crack of near constant crack front geometry. This is not true for corner cracks or elliptical surface crack geometries in the small crack regime where the crack front geometry is not symmetric or through-thickness. This affects similitude parameters that are based on the crack length. The hypothesis in this paper is that a comparison between long crack data and short crack data should be made using similar increments in crack surface area. The work applied to the specimen is dissipated in generation of fracture surface, whereas fracture length is a result. The crack surface area approach includes the two-dimensional effect of crack growth geometry in the small crack regime. A corner crack and a through crack are shown to follow the same power law relationship when using the crack area as base parameter. The crack front length is not constant, and its power law behaviour for a corner crack is shown.","","en","journal article","","","","","","","","","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:a0107e87-585b-4e02-ba26-44cfd5cf681e","http://resolver.tudelft.nl/uuid:a0107e87-585b-4e02-ba26-44cfd5cf681e","Towards a physics-based relationship for crack growth under different loading modes","Amaral, L. (TU Delft Structural Integrity & Composites); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials; TU Delft Structural Integrity & Composites)","","2018","In an attempt to understand quasi-static delamination growth under mixed mode loading conditions from a physics-based perspective, this work first evaluated cracking in isotropic materials. The critical Strain Energy Density (SED) approach is adopted, because physically the onset of crack growth is expected to occur when the energy available near the crack tip reaches a critical value. The main hypothesis of the present paper is that the critical SED for onset of crack growth is constant for a given material, and independent of the loading mode. The relationship derived from this hypothesis therefore relates the physical onset of crack growth and the angle at which that occurs for any opening mode through the SED. To test this hypothesis, results from literature were taken and shear fracture tests on foam specimens were performed, which both were compared with the derived relationship. The excellent correlation demonstrated the validity of the physics-based relationship, which explains the observed differences between mode I and mode II fracture toughnesses and illustrates why concepts like the Stress Intensity Factor (SIF) alone are insufficient to explain the observations. The developed relationship allows to derive the mode II fracture toughness from mode I fracture toughness tests and the material's mechanical properties.","","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2018-11-01","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:9f654671-a81a-4a4d-a7f8-b1bae4e7d73b","http://resolver.tudelft.nl/uuid:9f654671-a81a-4a4d-a7f8-b1bae4e7d73b","Using acoustic emission to understand fatigue crack growth within a single load cycle","Pascoe, J.A. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2018","Current methods for prediction of fatigue crack growth are based on empirical correlations which do not take the crack growth behaviour within a single cycle into account. To improve these prediction methods, more understanding of the physical mechanisms of crack growth is required. In this research the acoustic emission technique was used to investigate the crack growth behaviour during a single fatigue cycle. It was found that crack growth can potentially occur both during loading and unloading, but only while the strain energy release rate is above a crack growth (CG) threshold value. The results suggest this CG threshold value is the same in both quasi-static and fatigue loading. Further work is necessary to fully understand the link between the received acoustic emission signals and the actual crack growth processes. Nevertheless, the paper shows the potential of acoustic emission to provide more insight into the physics of crack growth.","Acoustic emission; Adhesive bonding; Crack growth; Fatigue","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2018-12-01","","","Structural Integrity & Composites","","",""
"uuid:fbaea3ac-1120-487b-87dc-87a93bd0b119","http://resolver.tudelft.nl/uuid:fbaea3ac-1120-487b-87dc-87a93bd0b119","Analytical solutions for crack opening displacements of eccentric cracks in thin-walled metallic plates","Wang, W. (TU Delft Structural Integrity & Composites); Rans, C.D. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2018","In the context of the prevalence of thin-walled metallic aerospace structures, the added resistance to crack propagation offered by a built-up structure is desirable from a damage tolerance standpoint. The analysis of failure in such structures, however, is limited by the lack of crack opening solutions. This paper develops analytical models that calculate crack opening displacements (CODs) for a more general cracking scenario, i.e. non-symmetric cracks. The proposed models are based on the Westergaard stress functions. It is then found that the COD solution of one model is particularly accurate. The potential significance of the obtained solutions lies in analysing failure in built-up structures containing non-symmetric cracks. The crack opening solution is particularly useful in estimating the load transfer between cracked body and intact bridging structures in built-up structures using the principle of displacement compatibility.","Crack opening displacement; Eccentric crack; Load redistribution; Stress intensity factor; Westergaard stress distribution","en","journal article","","","","","","","","2019-12-01","","","Structural Integrity & Composites","","",""
"uuid:a40335a3-0b7a-4c25-bded-719dcd10ff17","http://resolver.tudelft.nl/uuid:a40335a3-0b7a-4c25-bded-719dcd10ff17","Experimental assessment of the influence of welding process parameters on Lamb wave transmission across ultrasonically welded thermoplastic composite joints","Ochôa, Pedro (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials; TU Delft Structural Integrity & Composites)","","2018","One of the advantages of thermoplastic composites relative to their thermoset counterparts is the possibility of assembling components through welding. Ultrasonic welding in particular is very promising for industrialization. However, uncertainty in the fatigue and fracture behaviour of composites is still an obstacle to the full utilisation of these materials. Health monitoring is then of vital importance, and Lamb wave techniques have been widely recognised as some of the most promising approaches for that end. This paper presents the first experimental study about the influence of welding travel on the transmission of Lamb waves across ultrasonically welded thermoplastic composite joints in single-lap configuration. The main aim of this research is to start to understand how guided waves interact with the internal structure of ultrasonic welds, so that benign, manufacturing-related structural features can be distinguished from damaging ones in signal interpretation. The power transmission coefficient and the correlation coefficient proved to be suitable for analysing the wave propagation phenomena, allowing quantitative identification of small variations of weld-line thickness and intermolecular diffusion at the weld interface. The conclusions are used to develop a tentative damage detection criterion which can later on assist the design of a Lamb wave based structural health monitoring system for thermoplastic composite structures. The Lamb wave test results are backed up by phased-array inspections, which also provide some extra insight on the internal structure of ultrasonic welds.","Lamb wave; Structural health monitoring; Thermoplastic composite; Ultrasonic welding","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2021-12-22","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:0289262a-bc71-45ce-8d8d-0a9ead34a410","http://resolver.tudelft.nl/uuid:0289262a-bc71-45ce-8d8d-0a9ead34a410","Transducer Placement Option of Lamb Wave SHM System for Hotspot Damage Monitoring","Ewald, Vincentius (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2018","In this paper, we investigated transducer placement strategies for detecting cracks in primary aircraft structures using ultrasonic Structural Health Monitoring (SHM). The approach developed is for an expected damage location based on fracture mechanics, for example fatigue crack growth in a high stress location. To assess the performance of the developed approach, finite-element (FE) modelling of a damage-tolerant aluminum fuselage has been performed by introducing an artificial crack at a rivet hole into the structural FE model and assessing its influence on the Lamb wave propagation, compared to a baseline measurement simulation. The efficient practical sensor position was determined from the largest change in area that is covered by reflected and missing wave scatter using an additive color model. Blob detection algorithms were employed to determine the boundaries of this area and to calculate the blob centroid. To demonstrate that the technique can be generalized, the results from different crack lengths and from tilted crack are also presented.","sensor placement option; hotspot damage; Lamb wave; Structural Health Monitoring (SHM); finite element modelling; image processing; additive color model","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:98088174-5098-445f-835d-98363e193ed6","http://resolver.tudelft.nl/uuid:98088174-5098-445f-835d-98363e193ed6","Full-scale testing of an ultrasonic guided wave based structural health monitoring system for a thermoplastic composite aircraft primary structure","Ochôa, Pedro (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials; TU Delft Structural Integrity & Composites)","","2018","This paper describes the test campaign of an ultrasonic guided wave (GW) based structural health monitoring system (SHM) deployed on a full-scale stiffened panel of a thermoplastic composite horizontal stabilizer torsion box. The diagnostic capabilities of the SHM system were successfully evaluated by testing barely-visible impact damage of different severities, applied in different critical areas of the structure. The test campaign allowed the successful validation of a novel procedure to consistently and reliably design a piezoelectric transducer network. It also allowed the gathering of strong evidence that piezoelectric transducer technology has appropriate durability characteristics for real SHM applications. Finally, it enabled the study of the influence of audible structural vibrations on GW signals.","","en","conference paper","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2021-12-22","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:5118891b-9382-4aa0-ada4-e526096c51aa","http://resolver.tudelft.nl/uuid:5118891b-9382-4aa0-ada4-e526096c51aa","Incorporating Inductive Bias into Deep Learning: A Perspective from Automated Visual Inspection in Aircraft Maintenance","Ewald, Vincentius (TU Delft Structural Integrity & Composites); Goby, Xavier (Student TU Delft); Jansen, Hidde (Student TU Delft); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials; TU Delft Structural Integrity & Composites)","","2018","The near-term artificial intelligence, commonly referred as ‘weak AI’ in the last couple years was achieved thanks to the advances in machine learning (ML), particularly deep learning, which has currently the best in-class performance outperforming other machine learning algorithms. In the deep learning framework, many natural tasks such as object, image, and speech recognition that were impossible to be performed by classical ML algorithms in the previous decades can now be be done by typical home personal computer. Deep learning requires large amount of data that has to be rapidly collected (also known as ‘big data’) in order to create robust model parameters that are able to predict future occurrences of certain event. In some domains, a large dataset such as CIFAR-10, MNIST, or Kaggle exist already. However, in many other domains such as aircraft visual inspection, such a large dataset is not easily available and this clearly restricts deep learning to perform well to recognize material damage in aircraft structures. As many computer science researchers believe, we also think that in order to achieve a performance similar to human-level intelligence, AI could and should not start from scratch. Introducing an inductive bias into deep learning might be one solution to achieve that humanlevel intelligence. In this paper, we give an example how to incorporate aerospace domain knowledge into the development of deep learning algorithms. We performed a relatively simple procedure: we conducted fatigue testing of an aluminum plate that is typically used in aircraft fuselage and build a deep convolutional neural network that classifies crack length according to crack propagation curve obtained from fatigue test. The results of this network are then compared to the results of the same network that was not injected by domain knowledge","Automated Visual Inspection","en","conference paper","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2021-12-22","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:4da365b9-f9c8-4592-a119-64f48b91c681","http://resolver.tudelft.nl/uuid:4da365b9-f9c8-4592-a119-64f48b91c681","Carbon fiber-reinforced polymer pultrusions adhesively bonded inside aluminum joints: experimental and numerical study","Lavalette, N. (TU Delft Structural Integrity & Composites); Bergsma, O.K. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials; TU Delft Structural Integrity & Composites)","Watkins, Simon (editor); Mohamed, Abdulghani (editor)","2018","In the context of lightweight structure design for the transportation and robotics industries, new types of composite structures are being developed, in the form of trusses made of fiber-reinforced polymer composite members of small diameter. The main objective of this work is to study adhesive joints, bonding pultruded composite tubes inside aluminum pieces, numerically and experimentally. More specifically, the objective is to determine which numerical model is able to predict the joint strength the most accurately, and to examine the influence of several design parameters on the strength and weight of the joints. With this purpose, samples are manufactured with varying dimensions, and tested in tension until failure. Next to the manufacturing numerical models using either a continuum mechanics or a damage mechanics (CZM) approach are built. The comparison of the numerical results with the experimental results show that the damage mechanics approach results in the most accurate joint strength predictions. It is also found that increasing the adhesive overlap length has the highest impact on increasing the joint strength, and that reducing the adherend thickness has the highest impact on reducing the structural weight, while preserving the joint strength.","Adhesive bonding; Carbon fiber-reinforced polymer; Finite Element Method; Cohesive Zone Modelling; Trusses","en","conference paper","","","","","","","","","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:6061909a-a030-4cee-a9da-305970db17de","http://resolver.tudelft.nl/uuid:6061909a-a030-4cee-a9da-305970db17de","A 3-D finite element model for thermal analysis of laser assisted fiber placement","Çelik, O. (TU Delft Structural Integrity & Composites); Shroff, S. (TU Delft Aerospace Structures & Computational Mechanics); Teuwen, Julie J.E. (TU Delft Structural Integrity & Composites); Bergsma, O.K. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2018","Laser assisted automated tape or fiber placement (LATP/LAFP) with in-situ consolidation is a promising technique for manufacturing large structures, eliminating the limitations of autoclave curing. Currently, 2-D models are mostly preferred for the thermal analysis of the process. A 3-D, transient thermal finite element model is developed to analyze the effect of the alignment of the heat source with the tape laying direction and is compared with a model imitating a 2-D analysis space. This aspect of the process has not been considered in the literature so far. Effects of this aspect on temperature history and intimate contact evolution are presented.","","en","conference paper","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:ab7a5c5a-2d1b-423c-8860-a9b9f08cf270","http://resolver.tudelft.nl/uuid:ab7a5c5a-2d1b-423c-8860-a9b9f08cf270","Mode I fatigue delamination growth with fibre bridging in multidirectional composite laminates","Yao, Liaojun (Harbin Institute of Technology; Northwestern Polytechnical University); Sun, Yi (Harbin Institute of Technology); Guo, Licheng (Harbin Institute of Technology); Lyu, Xiuqi (Purdue University); Zhao, Meiying (Northwestern Polytechnical University); Jia, Liyong (AVIC the First Aircraft Institute); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2018","Fatigue delamination in multidirectional composite laminates was experimentally investigated in present study. Both the Paris relation and a modified Paris relation (with a new similitude parameter) were employed to interpret fatigue delamination with significant fibre bridging. The results clearly demonstrated that fatigue delamination was independent of fibre bridging, if a reasonable similitude parameter was used in data reduction. As a result, a master resistance curve can be fitted to determine fatigue crack growth with different amounts of fibre bridging. The energy principles were subsequently used to provide physical interpretation on fatigue delamination. The results indicated the energy release for the same fatigue crack growth remained constant with fibre bridging. Bridging fibres in most cases just periodically stored and released strain energy under fatigue loading, but had little contribution to real energy release. The master resistance curve was finally applied to predict fatigue delamination with fibre bridging. Acceptable agreement between predictions and experiments was achieved, demonstrating the validation of the modified Paris relation in fibre-bridged fatigue delamination study.","Delamination; Fatigue; Fibre bridging; Multidirectional composite laminates","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2021-01-01","","","Structural Integrity & Composites","","",""
"uuid:b8775a59-103f-4568-8040-d486e2c933bf","http://resolver.tudelft.nl/uuid:b8775a59-103f-4568-8040-d486e2c933bf","The effect of temperature on fatigue crack growth in FM94 epoxy adhesive bonds investigated by means of energy dissipation","Usman, M. (TU Delft Flight Performance and Propulsion); Pascoe, J.A. (TU Delft Structural Integrity & Composites); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials; TU Delft Structural Integrity & Composites)","","2018","The effect of temperature on fatigue crack growth in epoxy adhesive bonds was investigated for a range of temperatures from -55 to 80[U+202F]°C. The fatigue crack growth behaviour was characterised using both strain energy release rate (SERR) and by measurements of energy dissipation. It was found that for a given maximum SERR, or a given energy dissipation per cycle, crack growth rate was higher at higher temperatures.The resistance to crack growth (in terms of energy dissipation per unit crack growth) was linearly related to the maximum SERR, and this relationship was not affected by temperature. A number of tests did show anomalous behaviour, which could be linked to differences on the fracture surfaces. Previous work had found a power-law relationship between the amount of available energy and the applied cyclic work. This relationship was found to be insensitive to temperature changes in the range of 0[U+202F]°C to 40[U+202F]°C, but at -55[U+202F]°C and -20[U+202F]°C, as well as at 60[U+202F]°C and 80[U+202F]°C, the behaviour was affected by temperature. This could again be linked to differences on the fracture surfaces.It was concluded that temperature does not affect crack growth by directly affecting the failure mechanisms themselves, but rather by affecting which mechanisms are active.","Adhesive bonds; Energy dissipation; Fatigue crack growth; Temperature","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2020-02-09","","Aerospace Structures & Materials","Flight Performance and Propulsion","","",""
"uuid:27fe5546-9825-4871-af2e-2407270abba4","http://resolver.tudelft.nl/uuid:27fe5546-9825-4871-af2e-2407270abba4","Comparative study of adhesive joint designs for composite trusses based on numerical models","Lavalette, N. (TU Delft Structural Integrity & Composites); Bergsma, O.K. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials)","","2017","In the context of lightweight structure design for the transportation and robotics industries, new types of composite structures are being developed, in the form of trusses made of fiber-reinforced polymer composite members of small diameter (a few millimeters thick at most). Some concepts of wound trusses can be found in the literature, but in more general cases, for which a predefined wound truss shape is not usable, individual truss members must be joined together. The axial strength of the composite members allow them to carry a high load, and the joints between those members should be strong enough to carry this load as well. With the objective of developing an efficient joint design for an application in thin composite trusses (member thickness ranging from 0.5 to 5 mm), finite element models of several adhesive joint designs were built, and their strengths were compared. The comparison was made using the same joint configuration (number of members, member cross-sectional area, joint dimensions) and loading conditions. Adhesive failure was considered in this study, and the strength of each design was determined from the value of the peak maximum principal strain in the adhesive layer, as this failure criterion is suitable for the toughened adhesive material used in the models. A trade-off between the strength, weight and manufacturability of each joint design was made in order to conclude on their overall performance. Results suggested that, among the joint designs modelled, round-based composite rods inserted in a tubular metallic piece are the most efficient in terms of strength-to-weight ratio.","Bonded joints; Carbon fiber reinforced polymer; Finite element method; Numerical study; Trusses","en","journal article","","","","","","","","","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:d8c3c582-af01-4228-aaac-fc363054cd35","http://resolver.tudelft.nl/uuid:d8c3c582-af01-4228-aaac-fc363054cd35","Analytical prediction model for non-symmetric fatigue crack growth in Fibre Metal Laminates","Wang, W. (TU Delft Structural Integrity & Composites); Rans, C.D. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials)","","2017","This paper proposes an analytical model for predicting the non-symmetric crack growth and accompanying delamination growth in FMLs. The general approach of this model applies Linear Elastic Fracture Mechanics, the principle of superposition, and displacement compatibility based on the understanding of deformation behaviour in eccentrically cracked metal panels. The non-symmetric crack growth behaviour of two crack tips and accompanying asymmetric load transfer from the eccentrically cracked metal layers to the intact bridging fibres are successfully predicted with the model. The predicted crack growth rates and delamination evolution are compared to test data, good correlation is observed.","Crack opening displacement; Fibre metal laminates; Non-symmetric crack; Stress intensity factor","en","journal article","","","","","","","","2019-07-06","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:e9eda64b-b0f8-4f21-89b8-991fe6593b25","http://resolver.tudelft.nl/uuid:e9eda64b-b0f8-4f21-89b8-991fe6593b25","Understanding mixed-mode cyclic fatigue delamination growth in unidirectional composites: An experimental approach","Amaral, L. (TU Delft Structural Integrity & Composites); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials)","","2017","Due to the lack of fundamental knowledge of the physics behind delamination growth, certification authorities currently require that composite structures in aircraft are designed such that any delamination will not grow. This usually leads to an overdesign of the structure, hampering weight reductions. In real structures, delaminations tend to grow under a mix of modes I and II. Although some studies have tried to assess mixed-mode fatigue delamination, little progress was made in understanding the physics behind the problem. Therefore, this work scrutinizes mixed-mode fatigue delamination growth and examines experimentally the damage mechanisms that lead to fracture. To this aim, mixed-mode delamination fatigue tests were performed at different mode mixities, displacement ratios and maximum displacements. Selected fracture surfaces were analysed after the tests in a Scanning Electron Microscope to gain insight on the damage mechanisms. The physical Strain Energy Release Rate G∗ was used as the similitude parameter, enabling the characterization of fatigue mixed-mode delamination propagation. The results obtained show no displacement ratio or maximum displacement dependence. Furthermore, the energy dissipated per area of crack created is approximately constant for a given mode mixity. However, the analyses of the fracture surfaces and the correlation of the damage features with energy dissipation indicate that different damage mechanisms that might be activated under different loading parameters cause the resistance to delamination to change under a given loading mode.","","en","journal article","","","","","","","","2019-06-30","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:6ccd9290-1ec8-4503-ab7f-48dcb7b2291b","http://resolver.tudelft.nl/uuid:6ccd9290-1ec8-4503-ab7f-48dcb7b2291b","Reliability Analysis of an Ultrasonic Guided Wave Based Structural Health Monitoring System for a Carbon Fibre Reinforced Thermoplastic Torsion-box","Ochôa, Pedro (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials)","Chang, F.K. (editor); Kopsaftopoulos, F. (editor)","2017","Certification is the key step towards the implementation of structural health monitoring (SHM) as part of condition based maintenance programmes of aircraft fleets. That can only be accomplished by demonstration of system performance in multiple scenarios and in a statistically relevant way. This paper describes a fully computational approach for reliability assessment of an ultrasonic guided wave (GW) based SHM system for a full-scale stiffened panel of a horizontal stabilizer torsion-box entirely made of carbon fibre reinforced thermoplastic. A pseudo-stochastic nature is attributed to the damage index values calculated from the finite-element signals, allowing hit-miss data to be generated. That data is in turn employed for the computation of probability of detection curves and relative operating characteristics. The results of this research show that detailed damage diagnostics in full-scale complex composite structures can be achieved by using ultrasonic GWs under the hotspot monitoring philosophy. Moreover, it is demonstrated that properly validated models of the monitoring environment can be used for reliability analysis of GW based SHM systems for full-scale complex composite structures, thereby reducing the need for extensive and costly experimental test campaigns, which in turn can contribute to an acceleration of the establishment of a certification framework for SHM systems.
In anisotropic media, the phase velocity varies with direction of propagation of the ultrasonic beam. Hence, the slowness surface and its properties play an important role in the beam models which are based on the paraxial approximation. The beam from a single element transducer is well collimated. However the beam from individual array elements is not well collimated and may affect the beam propagation through the composite structure. In this paper, Multi modular Gaussian beam (MMGB) model based on the paraxial approximation is applied to study the propagation of beam from an ultrasonic array in transversely isotropic fibre-reinforced composites. The effect of the slowness surface properties on the beam diffraction and skew through the composite structure are studied along with the influence of array parameters on the beam propagation through the structure.
This work has demonstrated that the overall beam profile for quasi longitudinal beam from an ultrasonic array propagating in transversely isotropic fibre reinforced composites can be modelled as multi Gaussian beams. Simulation results are presented which illustrate the effects of? slowness properties on beam propagation in unidirectional CFRP in the symmetric planes.","Laser ultrasound; time of flight (TOF); welding; aerospace; carbon fiber composite","en","conference paper","","","","","","","","","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:6d2e8e01-3b48-478c-8199-590cd8f323a8","http://resolver.tudelft.nl/uuid:6d2e8e01-3b48-478c-8199-590cd8f323a8","Fibre bridging effect on the Paris relation for mode I fatigue delamination growth in composites with consideration of interface configuration","Yao, L. (Harbin Institute of Technology); Sun, Y. (Harbin Institute of Technology); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials); Zhao, M (Northwestern Polytechnical University)","","2017","Fibre bridging can significantly enhance delamination resistance making the use of a single Paris resistance curve to determine fatigue crack growth insufficient. An empirical Paris-type relation has been developed in a previous study to take fibre bridging into account in fatigue delamination growth. This relation was developed by correlating the Paris constants C and n to the amount of fibre bridging. This paper provides a further investigation on the interface configuration effect on fatigue delamination growth, illustrating the significance of fibre bridging. The results demonstrated that more bridging fibres can be generated in a multidirectional interface, making both log(C) and n significantly depend on fibre bridging. Thus, the method proposed in the previous study is further extended to take into account of the interface configuration effect.","","en","journal article","","","","","","","","2019-01-01","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:337ca47c-be33-46d5-a689-f10e37999926","http://resolver.tudelft.nl/uuid:337ca47c-be33-46d5-a689-f10e37999926","Stress ratio dependence of fiber bridging significance in mode I fatigue delamination growth of composite laminates","Yao, L. (Harbin Institute of Technology); Sun, Y. (Harbin Institute of Technology); Zhao, M (Northwestern Polytechnical University); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials)","","2017","This paper aims to investigate stress ratio effect on fibre bridging significance in mode I fatigue delamination growth of composite materials. Fatigue resistance curves (R-curves) of different stress ratios are determined and compared with the quasi-static R-curve. The fatigue R-curve of a high stress ratio is similar to the quasi-static results. However, fatigue resistance of a low stress ratio is smaller than quasi-static resistance. These indicate that fibre bridging significance is stress ratio dependent. More bridging fibres can be generated in delamination of a high stress ratio, as compared to that of a low stress ratio. This can lead to fatigue bridging laws are stress ratio dependent and fatigue delamination is block load sequence dependent.","B. Fatigue; B. Delamination; Fibre bridging; A. Polymer-matrix composites (PMCs)","en","journal article","","","","","","","","2019-01-01","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:0262d624-296d-4128-90e3-7db4365aa234","http://resolver.tudelft.nl/uuid:0262d624-296d-4128-90e3-7db4365aa234","Towards high-quality multi-spot-welded joints in thermoplastic composite structures","Zhao, T. (TU Delft Structural Integrity & Composites); Palardy, G. (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials)","","2017","Ultrasonic welding is a promising assembly technique for thermoplastic composites and it is well-suited for spot welding. In this study, two typical welding process control strategies, i.e. displacement-controlled and energy-controlled welding, were selected to manufacture spot-welded joints. The influence of different boundary conditions, provided by different welding jigs, on the welding process and the performance of thus-created welded joints were investigated. The optimum input energy was found dependent on the welding jigs, while the optimum displacement was consistent for achieving the maximum weld strength in both welding jigs. Therefore, displacement-controlled welding showed more potential in producing consistent welds in sequential multi-spot welding.","Fracture analysis; Mechanical behaviour; Thermoplastic composites; Ultrasonic spot welding; Welding process control","en","conference paper","International Committee on Composite Materials","","","","","","","","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:d6eecd09-2c23-477f-a404-7c1fe6fd5100","http://resolver.tudelft.nl/uuid:d6eecd09-2c23-477f-a404-7c1fe6fd5100","Effect of fiber-matrix adhesion on the creep behavior of CF/PPS composites: Temperature and physical aging characterization","Motta Dias, M.H.; Jansen, K.M.B.; Luinge, J.W.; Bersee, H.E.N.; Benedictus, R.","","2016","The influence of fiber-matrix adhesion on the linear viscoelastic creep behavior of ‘as received’ and ‘surface modified’ carbon fibers (AR-CF and SM-CF, respectively) reinforced polyphenylene sulfide (PPS) composite materials was investigated. Short-term tensile creep tests were performed on ±45° specimens under six different isothermal conditions, 40, 50, 60, 65, 70 and 75 °C. Physical aging effects were evaluated on both systems using the short-term test method established by Struik. The results showed that the shapes of the curves were affected neither by physical aging nor by the test temperature, allowing then superposition to be made. A unified model was proposed with a single physical aging and temperature-dependent shift factor, aT,te. It was suggested that the surface treatment carried out in SM-CF/PPS had two major effects on the creep response of CF/PPS composites at a reference temperature of 40 °C: a lowering of the initial compliance of about 25 % and a slowing down of the creep response of about 1.1 decade.","viscoelastic creep behavior; physical aging; CF/PPS composites; time aging; time superposition; time temperature superposition principle (TTSP)","en","journal article","Springer","","","","","","","","Aerospace Engineering","Aerospace Structures & Materials","","","",""
"uuid:8974dcbf-6456-4f77-940b-7bd903a6417c","http://resolver.tudelft.nl/uuid:8974dcbf-6456-4f77-940b-7bd903a6417c","Fatigue crack growth in residual stress fields","garcia, C (External organisation); Lotz, T (External organisation); Martinez, M.J. (TU Delft Structural Integrity & Composites); Artemev, A (External organisation); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2016","","","en","journal article","","","","","","harvest","","2018-12-01","","","Structural Integrity & Composites","","",""
"uuid:b0bdd6cd-9a7c-4584-9307-5d623c637594","http://resolver.tudelft.nl/uuid:b0bdd6cd-9a7c-4584-9307-5d623c637594","Online Remaining Fatigue Life Prognosis for Composite Materials Based on Strain Data and Stochastic Modeling","Eleftheroglou, N. (TU Delft Structural Integrity & Composites); Zarouchas, D. (TU Delft Structural Integrity & Composites); Loutas, T.H. (University of Patras); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials)","","2016","The present study utilizes a state-of-the-art stochastic modeling with structural health monitoring (SHM) data derived from strain measurements, in order to assess the remaining useful life (RUL) online in composite materials under fatigue loading. Non-Homogenous Hidden Semi Markov model (NHHSMM) is a suitable candidate with a rich mathematical structure capable of describing the composite’s multi-state damage evolution in time. The proposed model uses as input SHM data in the form of strain measurements obtained from the Digital Image Correlation (DIC) technique to a coupon-level constant amplitude fatigue test campaign. The obtained from the stochastic model RUL estimations are compared with the actual RUL and the effectiveness of the prognosis is discussed.","Composite materials; Fatigue; strain data; stochastic models","en","journal article","","","","","","","","","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:c785f276-c212-43c1-91ad-316eae7818b8","http://resolver.tudelft.nl/uuid:c785f276-c212-43c1-91ad-316eae7818b8","Strain Monitoring using a Rayleigh Backscattering System for a Composite UAV Wing Instrumented with an Embedded Optical Fiber","Martinez Bueno, P. (TU Delft Structural Integrity & Composites; Universidad Politécnica de Madrid); Martinez, M.J. (TU Delft Structural Integrity & Composites; Clarkson University); Rans, C.D. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials)","","2016","The primary objective of this research study was to evaluate the capabilities for measuring strain of a composite UAV wing with an embedded optical fiber connected to a Rayleigh backscattering distributed sensing system. This research paper summarizes the manufacturing procedure used during the instrumentation of the composite UAV wing. In addition, a Finite Element Model was developed in order to verify the strain distribution of this complex structure under static and dynamic loading conditions. The use of strain gauge data as a means for verification is presented as part of this research. Finally, fatigue tests were carried out to determine the longevity of the embedded fiber during the design life of the structure. The results demonstrate the ability of a distributed sensing system to obtain complex and accurate strain distributions on a single non-grated fiber. In addition, the findings demonstrate current limitations of the system for capturing accurate strain profiles in dynamic loading test cases.","Rayleigh Backscattering; Embedded Optical Fiber; Unmanned Aerial Vehicles; Strain Monitoring; Composite Wing; Distributed Sensing System","en","journal article","","","","","","","","","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:7317e2a8-2a52-4b67-a8f9-89756e12c483","http://resolver.tudelft.nl/uuid:7317e2a8-2a52-4b67-a8f9-89756e12c483","An experimental investigation into pin loading effects on fatigue crack growth in Fibre Metal Laminates","Zhang, Z. (TU Delft Structural Integrity & Composites; The First Aircraft Design and Research Institute of AVIC); Wang, W. (TU Delft Structural Integrity & Composites); Rans, C.D. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials)","","2016","This paper provides an experimental investigation into the pin loading effects on the crack growth behaviour in Fibre Metal Laminates. The pin loading effects and bypass loading effects are incorporated in two different tested joints. The analysis of the test results shows that pin loading dominates the crack growth only in the vicinity of the pin hole and the superposition method for analysing stress intensity factor in FMLs with pin loading effects can be applied.","fibre metal laminates; pin loading effects; Fatigue Crack Growth; superposition method","en","journal article","","","","","","","","","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:96cd7d1b-2b49-4762-95ce-54e4d646ff4c","http://resolver.tudelft.nl/uuid:96cd7d1b-2b49-4762-95ce-54e4d646ff4c","Mechanical behaviour of thermoplastic composites spot-welded and mechanically fastened joints: A preliminary comparison","Zhao, T. (TU Delft Structural Integrity & Composites); Palardy, G. (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Structural Integrity & Composites); Rans, C.D. (TU Delft Structural Integrity & Composites); Martinez, M.J. (Clarkson University); Benedictus, R. (TU Delft Aerospace Structures & Materials)","","2016","The in-plane and out-of-plane mechanical behaviour of both ultrasonically spot-welded and mechanically fastened joints was investigated by double-lap shear and pull-through tests, respectively. Spot-welded specimens showed comparable onset failure load and significantly higher joint stiffness compared to mechanical fasteners when carrying shear load. The failure modes and the damage within specimens were analysed after mechanical tests. Intralaminar failure and very limited damage on the out-most ply were found for welded specimens, whereas catastrophic through-the-thickness failure was observed for mechanically fastened joints. Based on the experimental outcomes, the mechanical performance and failure mechanisms of spot-welded joints were critically assessed in comparison to the mechanical fasteners .","Thermoplastic resin; Mechanical properties; Fractography; Joints/joining","en","journal article","","","","","","","","2019-01-01","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:4741f928-0e1a-4791-bd79-2869839db839","http://resolver.tudelft.nl/uuid:4741f928-0e1a-4791-bd79-2869839db839","Comparative analysis of in-plane and out-of-plane mechanical behaviour of spot-welded and mechaincally fastened joints in thermoplastic composites","Zhao, T. (TU Delft Structural Integrity & Composites); Palardy, G. (TU Delft Structural Integrity & Composites); Rans, C.D. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials)","Drechsler, K. (editor)","2016","Ultrasonic welding is a promising assembly technique for thermoplastic composites and it is well-suited for spot welding. In this paper, the in-plane and out-of-plane mechanical behaviour of ultrasonically spot-welded and mechanically fastened joints are investigated by double-lap shear and pull-through tests, respectively. Special attention was paid to the comparison of onset failure load and joint stiffness of both types of joints in either type of test. Fractography was utilized to analyse the teste specimens. Failure of welded specimens was found limited in the joints but catastrophic damage was introduced into composite substrates of mechanically fastened specimens. The possibility of the substitution for mechanically fastened joints by spot-welded joints is discussed.","Thermoplastic composites; spot-welded joint; mechanical behaviour; fracture analysis","en","conference paper","KIT","","","","","","","","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:0718d771-7e3a-4a95-a86a-d7a21f4332ae","http://resolver.tudelft.nl/uuid:0718d771-7e3a-4a95-a86a-d7a21f4332ae","Sensor Fusion for Shape Sensing: Theory and Numerical Simulation","de Mooij, C. (TU Delft Structural Integrity & Composites); Martinez, M.J. (TU Delft Structural Integrity & Composites; Clarkson University); Benedictus, R. (TU Delft Aerospace Structures & Materials)","","2016","Computing global strain distributions in complex aerospace and wind energy structures in quasi-real time is an important challenge for the aerospace and wind energy industry. Shape sensing is being considered as a potential means for obtaining global strain fields of complex structures. This is achieved through the use of inverse finite element methods (iFEM). Traditional shape sensing techniques use a variety of sensors in isolation. These isolated approaches lead to a number of drawbacks, including significant errors in the strain and/or displacement distributions that they determine. This study focuses on reducing these errors by combining data from various sensor types.
In order to achieve this objective, a new iFEM approach was developed to improve how shape sensing determines a structure’s deformation from distributed sensors. The method utilizes a procedure that minimizes a quadratic error functional, based on the difference between the theoretical and the measured strains and displacements. The analytical iFEM equations are discretized for use in a numerical model, which is used to analyze simulated sensor data. The simulated data is obtained from a FEM analysis of a structure loaded in bending, torsion and shear, in addition to experiencing combined loads. As with previous inverse methods, the error functional weights were employed to manage missing measurements and Tikhonov regularization was applied to guarantee smoothness of the numerical solution.
In this study, it has been shown that the new iFEM methodology can determine the structural deformations to within 1% of the FEM results for each of the load cases. In addition, the methodology is capable of achieving the same accuracy as single sensor type iFEM methods with a smaller total number of sensors. The single sensor type iFEM methods that were considered made use of only strain data or only displacement data. Finally, an experimental setup consisting of a simple cantilever plate structure was constructed in order to experimentally verify the newly developed iFEM algorithm. The experimental strain and displacement data were obtained utilizing a Rayleigh backscattering fiber optic distributed sensing system and MEMS sensors, respectively. Both of these sensor types were mounted on the structure and subjected to the load cases that were simulated in the FEM analysis.","","en","poster","","","","","","","","","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:951e5a33-58f6-4ce1-a0f4-e506595eded2","http://resolver.tudelft.nl/uuid:951e5a33-58f6-4ce1-a0f4-e506595eded2","On the physical interpretation of the R-ratio effect and the LEFM parameters used for fatigue crack growth in adhesive bonds","Pascoe, J.A. (TU Delft Structural Integrity & Composites); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials)","","2016","The available models for the prediction of fatigue crack growth in adhesive bonds rely on the similitude principle. In most cases, one of three similitude parameters based on the strain energy release rate (SERR) is used; i.e. Gmax, (Δ√G)2, or ΔG. In all cases it is usually observed that keeping the similitude parameter constant, and changing the R-ratio, results in a different crack growth rate. In this paper it is shown that this apparent ‘R-ratio’ effect is caused because the selected similitude parameter does not define a unique load cycle; a single value of the similitude parameter could correspond to infinitely many load cycles. The strain energy dissipation approach is used to show that the resistance to fatigue crack growth is related to the maximum applied load. The amount of energy available for crack growth is shown to be related to the applied cyclic work. With these relationships the R-ratio effects reported in literature can be qualitatively explained, purely in terms of the actual applied load cycle. Although it is possible that the material behaviour also depends on the R-ratio, the magnitude of these effects can only properly be determined if the applied load cycle is correctly described first.","Adhesive Bonds; Fatigue Crack Growth; LEFM; R-ratio","en","journal article","","","","","","","","2019-05-01","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:9323be3d-f473-4615-868c-7c8493741a43","http://resolver.tudelft.nl/uuid:9323be3d-f473-4615-868c-7c8493741a43","Experimental characterisation of Lamb wave propagation through thermoplastic composite ultrasonic welds","Ochôa, Pedro (TU Delft Structural Integrity & Composites); Villegas, I.F. (TU Delft Structural Integrity & Composites); Groves, R.M. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials)","","2016","Ultrasonic welding is a very promising technique for joining thermoplastic composite (TpC) components in aircraft primary structures [1, 2]. The potential introduction of new lightweight structures in civil aviation has been driving the change towards condition-based maintenance (CBM) as an alternative to the regular inspection interval approach [3]. In turn, CBM has been pushing forward the development of structural health monitoring (SHM) technology capable of reliably assessing the structural integrity of a component during flight or at pre-flight checks. Among all of them, Lamb wave techniques are widely recognised as some of the most promising approaches for SHM of composite structures [4].
Accurate quantitative damage assessment can only be performed if ultrasonic response changes can be unambiguously correlated to specific damages. That correlation requires the distinction of benign features from damaging ones. Therefore, before designing an SHM system for any component it is first necessary to understand the influence of several intrinsic characteristics of the undamaged joints on Lamb wave propagation. In the case of TpC ultrasonically welded (UW) joints, the cross-section is characterised by a very thin (~ 0.05 mm) polymeric weld-line between the laminated adherends, and a region within the two laminate layers adjacent to the weld-line which is affected by partial fusion of the matrix during the welding process [1, 2]. Although this heat-affected zone does not have a separation surface as the weld-line, it is expected to have different elastic properties to the rest of laminate.
Despite several computational and experimental investigations about Lamb-wave-based SHM of different types of composite structures, the interaction of Lamb waves with the unique properties of TpCUW joints has not been addressed yet. This paper presents the first experimental study about the influence of weld quality and adherend edge tapering on the propagation of Lamb waves through TpCUW single-lap joints. The main aim of this research is to understand how the guided wave interactions with the internal structure of TpC ultrasonic welds influence the scattering at a single-lap geometry. The conclusions can later be used to develop a model which will assist the design of a Lamb-wave-based SHM system for a TpC structure. The results from this study are also expected to provide some reverse-engineering insight on different weld qualities, ultimately contributing to the improvement of the manufacturing process of TpCUW joints.","","en","abstract","","","","","","","","","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:bcf920e1-ed25-4bf4-9b61-e7a45aadc20f","http://resolver.tudelft.nl/uuid:bcf920e1-ed25-4bf4-9b61-e7a45aadc20f","Characterising resistance to fatigue crack growth in adhesive bonds by measuring release of strain energy","Pascoe, J.A. (TU Delft Structural Integrity & Composites); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); Benedictus, R. (TU Delft Aerospace Structures & Materials)","Iacoviello, Francesco (editor); Susmel, Luca (editor); Firrao, Donato (editor); Ferro, Giuseppe (editor)","2016","Measurement of the energy dissipation during fatigue crack growth is used as a technique to gain more insight into the physics of the crack growth process. It is shown that the amount of energy dissipation required per unit of crack growth is determined by Gmax, whereas the total amount of energy available for crack growth in a single cycle is determined by G2","Adhesive Bonds; Fatigue Crack Growth; Strain Energy Dissipation","en","conference paper","Elsevier","","","","","","","","","Aerospace Structures & Materials","Structural Integrity & Composites","","",""
"uuid:9a1e402f-af91-429b-92dd-a631e9da56ca","http://resolver.tudelft.nl/uuid:9a1e402f-af91-429b-92dd-a631e9da56ca","Lamb wave dispersion time-domain study using a combined signal processing approach","Ochoa, P.; Groves, R.M.; Benedictus, R.","","2015","Ultrasonic Lamb wave techniques are described as one of the most encouraging developments for structural health monitoring of aerospace composite structures. The reliability of those techniques is highly dependent on the quality of signal processing algorithms capable of extracting useful information out of complex responses. When damage localization is involved, it is crucial to rigorously determine time-of-flight (TOF) of wave groups. Among the available methods for automated TOF extraction the Akaike Information Criterion (AIC) and the Hilbert Transform (HT) have become very popular. The first one detects the onsettime of a signal based on the minimization of the AIC function. The second one relies on the HT to define the response envelope, allowing maximum amplitude points to be used for time interval measurement. This paper focuses primarily on comparing the aforementioned methods in order to assess their reliability for TOF determination. Additionally, a combined AIC-HT approach is used to further quantify Lamb wave dispersion phenomena.","","en","conference paper","Vrije Universiteit Brussel","","","","","","","","Aerospace Engineering","Aerospace Structures & Materials","","","",""
"uuid:788dd88a-dae3-4506-abfa-0aae7b2b4450","http://resolver.tudelft.nl/uuid:788dd88a-dae3-4506-abfa-0aae7b2b4450","Sensor Fusion Applied To Shape Sensing: Theory and Numerical Proof-of-Concept (poster)","De Mooij, C.; Martinez, M.; Benedictus, R.","","2015","Existing shape sensing methods use individual sensor types, determining either strain or displacement well, but not both. More accurate shape sensing could improve load estimation, necessary for accurate life assessment of the structure.","","en","conference paper","","","","","","","","","Aerospace Engineering","","","","",""
"uuid:f1526ee5-521c-4378-b935-e8b9d993b8a3","http://resolver.tudelft.nl/uuid:f1526ee5-521c-4378-b935-e8b9d993b8a3","Two-dimensional and transient thermal model of the continuous tape laying process","Skandali, M.; Jansen, K.M.B.; Koussios, S.; Sinke, J.; Benedictus, R.","","2015","The purpose of this study is to simulate the two-dimensional, transient and continuous heat transfer during the thermoset Automated Tape Laying (ATL) process. The heat transfer analysis is coupled with a cure kinetics model of the thermoset prepreg tapes used for the process. Unlike most studies, the process is modelled in a Lagrangian framework and is based on the realistic boundary conditions of the ATL such as the stepwise laying down of the tapes. The model results provide information about the temperature values at any time and any location inside the thermoset composite tapes. The temperature simulation results of the model were compared with experiments. Three layers of unidirectional prepreg tapes were laid down on an aluminium mould by the TU Delft ATL machine. The experimental results were obtained from thermocouples and pyrometers placed at various locations in the lay-up and on the robotic head, respectively. The comparison between the numerical and experimental results generated three main findings. First, the pyrometer values and the thermocouple values provide insight into how important is the contact between the mould and the first layer. Secondly, the temperature fading out which was witnessed by the thermocouple measurements and could not entirely be captured by the model provided information about the influence of the heat transfer coefficients on the model predictions. Thirdly, the peak temperature magnitudes of the numerical predictions appeared to generally compare well with the experimental results. Overall, the code can be used for different parameter values such as different line speed, heated length and power of the heat source and, can predict the temperature distribution inside the composite.","tape laying; cure; heat transfer; numerical","en","conference paper","ICCM","","","","","","","","Aerospace Engineering","Aerospace Structures & Materials","","","",""
"uuid:5c2f44b9-97a1-4ee6-9ab8-b8251ee57698","http://resolver.tudelft.nl/uuid:5c2f44b9-97a1-4ee6-9ab8-b8251ee57698","Influence of temperature on strength and failure mechanisms of resistance welded thermoplastic composites joints","Koutras, N.; Fernandez Villegas, I.; Benedictus, R.","","2015","In this work, the effect of temperature exposure on the strength of resistance welded joints is analysed. Glass fibre polyphenylene sulphide (GF/PPS) laminates were joined using the resistance welding technique and a stainless steel metal mesh as the heating element. Single lap shear tests at temperatures between 20°C and 150°C were performed to evaluate the strength of the welded joints and fractography was used to investigate changes in the failure mechanisms at elevated temperatures. The results show a strength reduction of 10-15% for the samples tested at temperatures up to 90°C, and a strength reduction of 22% and 38% for the samples tested at 120°C and 150°C, respectively, while the fracture surfaces observation revealed changes in the failure mechanisms of the welded joints tested at elevated temperatures.","thermoplastic composites; resistance welding; temperature; joint strength; failure mechanism","en","conference paper","ICCM","","","","","","","","Aerospace Engineering","Aerospace Structures & Materials","","","",""
"uuid:6ad6375b-31b8-4b7b-91b3-f68ece3132f0","http://resolver.tudelft.nl/uuid:6ad6375b-31b8-4b7b-91b3-f68ece3132f0","The concept of fatigue fracture toughness in fatigue delamination growth behavior","Yao, L.; Alderliesten, R.C.; Benedictus, R.","","2015","This paper provides a study on mode I fatigue delamination growth in composite laminates using energy principles. Experimental data has been obtained from fatigue tests conducted on Double Cantilever Beam (DCB) specimens at various stress ratios. A concept of fatigue fracture toughness is proposed to interpret the stress ratio effect in crack growth. The fatigue fracture toughness is demonstrated to be significantly stress ratio dependent. An explanation for this phenomenon is given using SEM fractography. Fracture surface is observed to be rougher for high stress ratio in comparison with that for low stress ratio, causing the fatigue resistance increase. Therefore, the stress ratio effect in fatigue crack growth can be physically explained by a difference in resistance to crack growth.","energy principles; fatigue delamination; fracture toughness; composite laminates","en","conference paper","ICCM","","","","","","","","Aerospace Engineering","Aerospace Structures & Materials","","","",""
"uuid:9cf82c49-3e69-45d2-aee8-78727f8064cc","http://resolver.tudelft.nl/uuid:9cf82c49-3e69-45d2-aee8-78727f8064cc","Simulation and detection of flaws in pre-cured CFRP using laser displacement sensing","Miesen, N.; Sinke, J.; Groves, R.M.; Benedictus, R.","","2015","The novelty of the research is the detection of different types of flaws in the prepreg carbon fibre-reinforced fibres (CFRP) layup compared to in cured products. This paper presents the development of a new method for in situ detection of prepreg CFRP production flaws combining laser displacement sensors and analytical modelling. Experimental results are used to validate the results from the models. The pre-cured flaws are simulated to determine the needed specifications of the measurement system. In static and dynamic experiments, the typical production flaws are detected to demonstrate the use of laser displacement sensing as a preventative non-destructive evaluation (NDE) system. During the production of CFRP materials, flaws can be introduced due to the process of layup or curing. Once a production flaw is embedded and cured in the CFRP laminate, the damage is irreversible and it is expensive to rework or remanufacture the product. Laser displacement sensing is currently used in a wide range of applications in industrial manufacturing and is successfully assessed in this research as a preventative NDE system.","laser displacement sensing; preventative NDE; CFRP; layup process","en","journal article","Springer","","","","","","","","Aerospace Engineering","Aerospace Structures & Materials","","","",""
"uuid:23f260da-c0cc-4e23-97c8-57c21b9efa50","http://resolver.tudelft.nl/uuid:23f260da-c0cc-4e23-97c8-57c21b9efa50","Energy based study of quasi-static delamination as a low cycle fatigue process","Amaral, L.; Yao, L.; Alderliesten, R.C.; Benedictus, R.","","2015","This work proposes to treat quasi-static mode I delamination growth of CFRP as a low-cycle fatigue process. To this end, mode I quasi-static and fatigue delamination tests were performed. An average physical Strain Energy Release Rate (SERR), derived from an energy balance, is used to characterize the energy released in crack extension. The physical SERR is then compared to the SERRs calculated by the ASTM standard, and the physical background of the standard is questioned. Furthermore, when normalizing the physical SERR for fatigue delamination by the one obtained for quasi-static crack extension, a stress ratio dependence is observed. This stress ratio effect is physically explained to be present due to the relation between quasi-static and fatigue loading at high stress ratios.","","en","conference paper","VTT Technical Research Centre of Finland","","","","","","","","Aerospace Engineering","Aerospace Structures and Materials","","","",""
"uuid:1a3238c4-4c8d-49a1-8319-9c2b5a12a068","http://resolver.tudelft.nl/uuid:1a3238c4-4c8d-49a1-8319-9c2b5a12a068","On the relationship between disbond growth and the release of strain energy","Pascoe, J.A.; Alderliesten, R.C.; Benedictus, R.","","2014","Current prediction methods for growth of disbonds under fatigue loading are generally based on a correlation with either the maximum strain energy release rate (SERR) or the SERR range. This paper highlights some issues with this approach. In particular, it is argued that the maximum SERR or the SERR range alone do not give sufficient information to uniquely characterize the driving force for crack growth. Furthermore it is argued that the relationship between crack growth rate and loss of strain energy should be considered on the scale of the entire load cycle. By means of disbond growth experiments it is shown that there is indeed a very strong correlation between the crack growth rate and the strain energy lost during a fatigue cycle. Unlike methods based on the SERR, this correlation is not affected by the R-ratio. Based on the found correlation a possible basis for a new approach to disbond growth prediction is suggested.","adhesive bonding; crack growth; fatigue; fracture mechanics","en","journal article","Elsevier","","","","","","","","Aerospace Engineering","Aerospace Structures and Materials","","","",""
"uuid:1e55ca20-c0b2-449f-904b-4921d04189ae","http://resolver.tudelft.nl/uuid:1e55ca20-c0b2-449f-904b-4921d04189ae","Optical coherence elastography for measuring the deformation within glass fiber composite","Liu, P.; Groves, R.M.; Benedictus, R.","","2014","Optical coherence elastography (OCE) has been applied to the study of microscopic deformation in biological tissue under compressive stress for more than a decade. In this paper, OCE has been extended for the first time, to the best of our knowledge, to deformation measurement in a glass fiber composite in the field of nondestructive testing. A customized optical coherence tomography system, combined with a mechanical loading setup, was developed to provide pairs of prestressed and stressed structural images. The speckle tracking algorithm, based on 2D cross correlation, was used to estimate the local displacements in micrometer scale. The algorithm was first evaluated by a test of rigid body translation. Then the experiments were carried out with the tensile test and three point bending on a set of glass fiber composites. The structural features and structural variations during the mechanical loadings are clearly observed with the presented displacement maps. The advantages and prospects for OCE application on glass fiber composites are discussed at the end of this paper.","optical coherence tomography; tomographic image processing; speckle imaging; nondestructive testing","en","journal article","Optical Society of America","","","","","","","","Aerospace Engineering","Aerospace Structures & Materials","","","",""
"uuid:3bd7b897-2206-479d-a712-93ea5e9732c7","http://resolver.tudelft.nl/uuid:3bd7b897-2206-479d-a712-93ea5e9732c7","Towards Understanding Fatigue Disbond Growth via Cyclic Strain Energy","Pascoe, J.A.; Alderliesten, R.C.; Benedictus, R.","","2014","The concept of relating fatigue disbond growth to the strain energy release rate (SERR) is critically examined. It is highlighted that the common practise of using only the maximum SERR or only the SERR range is insufficient to correctly characterize a load cycle. As crack growth requires energy, it is argued that growth should be related to the total amount of energy released during a fatigue cycle, and not to the amount of energy that would be released by a crack growth increment under the instantaneous load conditions at one point in the load cycle. This argument is supported by experimental evidence, showing that the relationship between fatigue disbond growth (FDG) rate and either maximum SERR or SERR range is R-ratio dependent, whereas the relationship between FDG rate and the loss of strain energy is not.","adhesive Bonding; fatigue; disbond growth; energy method","en","journal article","Elsevier","","","","","","","","Aerospace Engineering","Aerospace Structures & Materials","","","",""
"uuid:e22dcf36-b9be-4b7a-b7fa-4626e8d5f393","http://resolver.tudelft.nl/uuid:e22dcf36-b9be-4b7a-b7fa-4626e8d5f393","Methods for the prediction of fatigue delamination growth in composites and adhesive bonds: A critical review","Pascoe, J.A.; Alderliesten, R.C.; Benedictus, R.","","2013","An overview is given of the development of methods for the prediction of fatigue driven delamination growth over the past 40 years. Four categories of methods are identified: stress/strain-based models, fracture mechanics based models, cohesive-zone models, and models using the extended finite element method. It is highlighted that most models are phenomenological, based on the observed macro-scale behaviour of test specimens. It is suggested that a more physics based approach, focusing on elucidating the mechanisms involved, is needed to come to a full understanding of the problem of delamination growth.","delamination; fatigue; linear elastic fracture mechanics; cohesive zone model; XFEM","en","journal article","Elsevier","","","","","","","2013-11-07","Aerospace Engineering","Aerospace Structures & Materials","","","",""
"uuid:9efa0245-e3be-4ff9-a6e4-33c49fa8dbd1","http://resolver.tudelft.nl/uuid:9efa0245-e3be-4ff9-a6e4-33c49fa8dbd1","Study of the fire resistant behavior of unfilled and carbon nanofibers reinforced polybenzimidazole coating for structural applications","Iqbal, H.M.S.; Stec, A.A.; Patel, P.; Bhowmik, S.; Benedictus, R.","","2013","With increasing interest in epoxy-based carbon fiber composites for structural applications, it is important to improve the fire resistant properties of these materials. The fire resistant performance of these materials can be improved either by using high performance epoxy resin for manufacturing carbon fiber composite or by protecting the previously used epoxy-based composite with some fire resistant coating. In this context, work is carried out to evaluate the fire resistance performance of recently emerged high performance polybenzimidazole (PBI) when used as a coating material. Furthermore, the effect of carbon nanofibers (CNFs) on fire resistant properties of inherently flame retardant PBI coating was studied. Thermogravimetric analysis of carbon/epoxy composite, unfilled PBI and nano-filled PBI shows that the carbon/epoxy composite maintained its thermal stability up to a temperature of 400°C and afterwards showed a large decrease in mass, while both unfilled PBI and nano-filled PBI have shown thermal stability up to a temperature of 575°C corresponding to only 11% weight loss. Cone calorimeter test results show that unfilled PBI coating did not improve the fire retardant performance of carbon/epoxy composite. Conversely, nano-filled PBI coating has shown a significant improvement in fire retardant performance of the carbon/epoxy composite in terms of increased ignition time, reduced average and peak heat release rate and reduced smoke and carbon monoxide emission. These results indicate that addition of carbon nanofibers to inherently flame retardant coating can significantly be helpful for improving the fire resistance performance of composite materials even with low coating thickness.","structural composite; fire resistant coating; carbon nanofibers","en","journal article","Wiley","","","","","","","","Aerospace Engineering","Aerospace Structures & Materials","","","",""
"uuid:0e2b720d-4182-4c25-8c70-33e3405a080b","http://resolver.tudelft.nl/uuid:0e2b720d-4182-4c25-8c70-33e3405a080b","Signal processing in optical coherence tomography for aerospace material characterization","Liu, P.; Groves, R.M.; Benedictus, R.","","2013","Based on a customized time-domain optical coherence tomography (OCT) system, a series of signal processing approaches have been designed and reviewed. To improve demodulation accuracy and image quality, demodulation approaches such as median filter, Hilbert transform, and envelope detector were investigated with simulated as well as experimental data. Without noise, the Hilbert transform has the best performance, but after considering the narrow-band noise in the modulated signal, the envelope detector was selected as the ideal demodulation technique. To reduce noise and enhance image contrast, digital signal processing techniques such as a bandpass filtering and two-dimensional median filtering were applied before and after the demodulation, respectively. Finally with integration of the customized OCT setup and designed signal processing algorithms, aerospace materials, such as polymer coatings and glass-fiber composites, were successfully characterized. The cross-sectional images obtained clearly show the microstructures of the materials.","optical coherence tomography; signal processing; demodulation; median filter; aerospace materials; microstructure","en","journal article","SPIE (International Society for Optical Engineering)","","","","","","","","Aerospace Engineering","Aerspace Structures and Materials","","","",""
"uuid:21c6398e-9836-4bf0-8ae4-75f2d29a5d1b","http://resolver.tudelft.nl/uuid:21c6398e-9836-4bf0-8ae4-75f2d29a5d1b","Damage evolution in GLARE fibre-metal laminate under repeated low-velocity impact tests","Morinière, F.D.; Alderliesten, R.C.; Tooski, M.Y.; Benedictus, R.","","2012","An experimental study was performed on the repeated low-velocity impact behaviour of GLARE. Damage evolution in the material constituents was characterised with successive number of impacts. Records were correlated with visual inspection, ultrasound C-scan and chemical etching. The stiffness of the plate varied when cumulating the number of impacts. Damage accumulation was limited thanks to the synthesis of unidirectional composite and metal. The glass/epoxy plies with high elastic tensile strength could withstand several impacts before perforation despite delamination growth in the vicinity of the impacted area. The damage tolerant aluminium layers prevented the penetration of the projectile and avoided the expansion of delamination. This efficient mechanism preserved the structural integrity of GLARE until first aluminium cracking at the non-impacted side. Among the different failure modes, plate deformation absorbed most of the impact energy. The findings will support the development of a generic quasi-static analytical model and numerical methods.","low-velocity impact; GLARE 5 FML; delamination; C-scan; chemical etching","en","journal article","Springer-Verlag","","","","","","","","Aerospace Engineering","Aerspace Structures and Materials","","","",""
"uuid:08d5d3d5-a946-4f59-b5d8-ec7ed3b3658b","http://resolver.tudelft.nl/uuid:08d5d3d5-a946-4f59-b5d8-ec7ed3b3658b","Experimental and Numerical Investigation of Metal Type and Thickness Effects on the Impact Resistance of Fiber Metal Laminates","Sadighi, M.; Pärnänen, T.; Alderliesten, R.C.; Sayeaftabi, M.; Benedictus, R.","","2012","The impact response of fiber metal laminates (FMLs), has been investigated with experiments and numerical simulations, which is reported in this article. Low-velocity impacts were carried out to study the effects of metal type and thickness within FMLs. Glare5-3/2 laminates with two aluminum layer thicknesses and a similar FML containing magnesium sheets were impacted by drop weight tests. Also, a major part of this study was to accomplish a dynamic non-linear transient analysis to study the impact response of FMLs using the commercial finite element (FE) analysis code ABAQUS. By reviewing different approaches of modeling constituents of an FML, it is shown that the appropriate selection of elements hasmore significant role than failure criterion to predict acceptable results for this type of laminate and loading. The good agreement obtained between experimental and numerical results verifies the possibility of relatively simpler simulation by FE-analysis to predict overall response of FMLs under impact loading.","fiber metal laminates; magnesium; low velocity impact; numerical modeling; abaqus","en","journal article","Springer-Verlag","","","","","","","","Aerospace Engineering","Aerspace Structures and Materials","","","",""
"uuid:bb2821fd-862b-45f2-a330-ca07de01c4cb","http://resolver.tudelft.nl/uuid:bb2821fd-862b-45f2-a330-ca07de01c4cb","Development of fibre-metal laminates for improved impact performance","Morinière, F.D.; Alderliesten, R.C.; Benedictus, R.","","2012","An analytical and experimental investigation into the low-velocity behaviour of GLARE Fibre-Metal Laminates (FMLs) has been performed. A quasi-static approach was developed to estimate the perforation energy absorbed between the constituents of GLARE. The analysis considered contact area increase during perforation and strain rate effect on material properties. Particular attention was paid to the effect of ply-angle orientation and aluminium position. Predicted maximum impact force, maximum displacement, and perforation energy related to impact velocity were within 10% of test results. Stacking composite plies oriented along the diagonal of the plate with more than 2 aluminium layers leads to a more impact resistant FML. The generic nature of the developed methodology can support the optimization of high-performance FML concepts","","en","journal article","Springer-Verlag","","","","","","","","Aerospace Engineering","Aerspace Structures and Materials","","","",""
"uuid:bc9b9c96-abcb-4b59-b361-0d678e0aabcd","http://resolver.tudelft.nl/uuid:bc9b9c96-abcb-4b59-b361-0d678e0aabcd","Laminate and airplane provided with such a laminate","Alderliesten, R.C.; Benedictus, R.; Rans, C.D.","","2012","","","en","patent","European Patent Office","","","","","","","","Aerospace Engineering","Aerospace Materials & Manufacturing","","","",""
"uuid:f6da89bd-b155-4545-90ac-8a4548c15489","http://resolver.tudelft.nl/uuid:f6da89bd-b155-4545-90ac-8a4548c15489","The generation of deformation damage during fatigue loading in Al-Cu alloy studied by the Doppler Broadening technique","Ruiz-Ripoll, M.L.; Schut, H.; Van Dijk, N.H.; Alderliesten, R.C.; Van der Zwaag, S.; Benedictus, R.","","2011","We have investigated the evolution of damage during fatigue loading in Al–Cu 2024-T3 alloys using the positron annihilation Doppler Broadening (DB) technique. This technique enables us to monitor in a non destructive way, at the atomic and vacancy level, the formation of deformation defects and their interaction with solute atoms at selected stages of fatigue testing. The changes in the S and W Doppler Broadening parameters are linked to the changes in fatigue behavior at lower stress levels. The material was tested under constant amplitude fatigue loading at four different stress levels and DB tests were conducted at selected stages of fatigue lifetime. The results are compared to those obtained during static tensile tests.","","en","conference paper","IOP Publishing","","","","","","","","Aerospace Engineering","Aerspace Structures and Materials","","","",""
"uuid:8c901715-96e7-4f5c-aac1-d92583f4d570","http://resolver.tudelft.nl/uuid:8c901715-96e7-4f5c-aac1-d92583f4d570","Fatigue properties of AA2024 for intermittent thermal healing and analysis of damage development using positron annihilation Doppler broadening technique (abstract)","Ruiz-Ripoll, M.L.; Schut, H.; Benedictus, R.; Van der Zwaag, S.; Alderliesten, R.C.","","2011","","self-healing; aluminum alloy; fatigue load; positron annihilation Doppler broadening","en","conference paper","","","","","","","","","Delft University of Technology","","","","",""
"uuid:05b58c75-b74f-48ac-905d-d202e31be958","http://resolver.tudelft.nl/uuid:05b58c75-b74f-48ac-905d-d202e31be958","Lamb wave detection in prepreg composite materials with fibre Bragg grating sensors","Miesen, N.; Mizutani, Y.; Groves, R.M.; Sinke, J.; Benedictus, R.","","2011","This paper demonstrates that existing Structural Health Monitoring (SHM) techniques have potential during the production phase in addition to their application for maintenance and for in-flight monitoring. Flaws occur during composite fabrication in industry, due to an imperfect process control and human errors. This decreases production efficiency and increases costs. In this paper, the monitoring of Lamb waves in unidirectional carbon fibre (UD-CFRP) prepreg material is demonstrated using both Fibre Bragg Gratings (FBG)s and piezolectric acoustic sensors, and that these SHM sensors may be used for flaw detection and production monitoring. The detection of Lamb waves in a one ply thick sheet of prepreg UD-CFRP material is demonstrated for an FBG sensor aligned with the carbon fibre orientation and bonded to the surface of the prepreg, Furthermore, the velocity of Lamb waves in prepreg UD-CFRP in different orientations is investigated. Finally the successful detection of a material crack in a prepreg UD-CFRP sheet using the Lamb wave detection method is demonstrated.","FBG; composites; damage detection; Lamb waves","en","conference paper","SPIE","","","","","","","","Aerospace Engineering","Aerospace Materials and Manufacturing","","","",""
"uuid:9f3f5b65-7ddc-4280-8f2a-cc726ade8cd8","http://resolver.tudelft.nl/uuid:9f3f5b65-7ddc-4280-8f2a-cc726ade8cd8","Global and Local Mechanical Properties and Microstructure of Friction Stir Welds with Dissimilar Materials and/or Thicknesses","Zadpoor, A.A.; Sinke, J.; Benedictus, R.","","2010","This article studies the properties of a wide range of friction-stir-welded joints with dissimilar aluminum alloys or thicknesses. Two aluminum alloys, namely, 2024-T3 and 7075-T6, are selected for the study and are welded in ten different combinations of alloys and thicknesses. The welding parameters are optimized for each configuration, and a systematic study of the effects of material and thickness combinations on the microstructural features, global and local mechanical properties, and fracture mechanisms of the welds is carried out. It is shown that dissimilar alloys are extruded into each other, the texture is heterogeneous in the weld zone, and that there is no significant diffusion of alloying elements between the alloys. For most configurations, the local and global mechanical properties decrease as the thickness ratio increases. The local yield strength and plasticity parameters substantially vary next to the weld centerline, hence requiring their implementation in finite element method (FEM) models. Machining to obtain a constant thickness significantly influences the mechanical properties of the welds. The fracture mechanism is found to be a mixture of ductile and brittle fractures and to qualify as ‘‘quasi-cleavage.’’","","en","journal article","Springer","","","","","","","","Mechanical, Maritime and Materials Engineering","Materials Science and Engineering","","","",""
"uuid:659bd838-09f3-4dcd-a553-bad1ff5e5648","http://resolver.tudelft.nl/uuid:659bd838-09f3-4dcd-a553-bad1ff5e5648","The generation of deformation damage during fatigue loading in Al-Cu alloy studied by the Doppler Broadening technique","Ruiz Ripoll, ML (TU Delft RST/Neutron and Positron Methods in Materials); Schut, H. (TU Delft RST/Neutron and Positron Methods in Materials); Alderliesten, R.C. (TU Delft Structural Integrity & Composites); van der Zwaag, S. (TU Delft Novel Aerospace Materials); Benedictus, R. (TU Delft Structural Integrity & Composites)","Buckman, S (editor)","2010","We have investigated the evolution of damage during fatigue loading in Al-Cu 2024-T3 alloys using the positron annihilation Doppler Broadening (DB) technique. This technique enables us to monitor in a non destructive way, at the atomic and vacancy level, the formation of deformation defects and their interaction with solute atoms at selected stages of fatigue testing. The changes in the S and W Doppler Broadening parameters are linked to the changes in fatigue behavior at lower stress levels. The material was tested under constant amplitude fatigue loading at four different stress levels and DB tests were conducted at selected stages of fatigue lifetime. The results are compared to those obtained during static tensile tests.","Conf.proc. > 3 pag","en","conference paper","ARC Centre of Excellence for Antimatter-Matter Studies","","","","","","","","","","RST/Neutron and Positron Methods in Materials","","",""
"uuid:7a8981d6-ce65-4a63-97c4-78bfe735e27a","http://resolver.tudelft.nl/uuid:7a8981d6-ce65-4a63-97c4-78bfe735e27a","Variable Amplitude Fatigue of FMLs On Developing a Mechanistic Understanding","Rans, C.; Alderdiesten, R.; Benedictus, R.; Khan, S.","","2009","Presentation on conference","","en","conference paper","Delft University of Technology","","","","","","","","Aerospace Engineering","","","","",""
"uuid:53f19ab4-a579-4ca1-a914-241d8ccafe7e","http://resolver.tudelft.nl/uuid:53f19ab4-a579-4ca1-a914-241d8ccafe7e","Understanding the Fatigue Behavior of FML Structures and Materials under Complex Variable Amplitude Loading","Alderdiesten, R.; Benedictus, R.; Khan, S.","","2009","This paper presents various failure mechanisms in FMLs, highlights the presence or absence of interaction effects, and describes how the failure mechanisms can be described for predicting damage growth under arbitrary complex load spectra.","","en","conference paper","Delft University of Technology","","","","","","","","Aerospace Engineering","","","","",""
"uuid:7ef4ef66-aeda-4b44-90f8-a33ec0e714e7","http://resolver.tudelft.nl/uuid:7ef4ef66-aeda-4b44-90f8-a33ec0e714e7","Experimental and numerical analysis of a beam made of adhesively bonded tailor-made blanks","Monaco, A.; Sinke, J.; Benedictus, R.","","2008","For aircraft structures, it is clear that the design and the selection of materials play an important role in the performance of the aircraft. The production costs are also important. The concept of tailor-made blanks (TMBs) is based on the use of dedicated blanks, made of different alloys and/or thickness in order to satisfy different demands such as an increase, if necessary, of local strength, stiffness, and damage tolerance. This paper describes the results of a study to assess the potential weight and cost savings of using TMBs in a typical aerospace structure. A bonded structure representing the floor beam of an aircraft has been selected, analyzed, and tested to validate the numerical and analytical predictions made with MATLAB and finite-element method. The results show weight reduction of 12% and 37% for two studied configurations, compared to the reference beam.","Tailor-made blanks; Adhesive bonding; FEM modeling; Safety factor; Failure","en","journal article","Springer","","","","","","","","Aerospace Engineering","Mechanics, Aerospace Structures and Materials","","","",""
"uuid:a08e4e99-9095-473f-8a4f-39592b3b03d5","http://resolver.tudelft.nl/uuid:a08e4e99-9095-473f-8a4f-39592b3b03d5","Epoxy-resin adhesive and method for bonding using such an epoxy resin adhesive","Bhowmik, S.; Poulis, J.A.; Benedictus, R.","","2008","The invention relates to an epoxy resin adhesive comprising a dotation of nano-substances, wherein the nano- substances are selected from the group comprising carbon-fibre nanotubes, carbon nano-fibres, silicate nano powders, and wherein the nano-substances are dispersed in the adhesive with a weight ratio of at least 1% and wherein the nano-substances are carbon-fibre nanotubes having a weight ratio of approximately 2%.","","en","patent","European Patent Office","","","","","","","","Aerospace Engineering","","","","",""
"uuid:85fdac44-ca9e-4421-b2e2-bb9b8ee509d8","http://resolver.tudelft.nl/uuid:85fdac44-ca9e-4421-b2e2-bb9b8ee509d8","The Einstein relation in quantum wires of III-V, ternary, and quaternary materials in the presence of light waves: Simplified theory, relative comparison, and suggestion for experimental determination","Ghatak, K.P.; Bhattacharya, S.; Bhowmik, S.; Benedictus, R.; Choudhury, S.","","2008","We study the Einstein relation for the diffusivity to mobility ratio (DMR) in quantum wires (QWs) of III-V, ternary, and quaternary materials in the presence of light waves, whose unperturbed energy band structures are defined by the three band model of Kane. It has been found, taking n-InAs, n-InSb, n-Hg1?xCdxTe, n-In1?xGaxAsyP1?y lattice matched to InP as examples, that the respective DMRs exhibit decreasing quantum step dependence with the increasing film thickness, decreasing electron statistics, increasing light intensity and wavelength, with different numerical values. The nature of the variations is totally band structure dependent and is influenced by the presence of the different energy band constants. The strong dependence of the DMR on both the light intensity and the wavelength reflects the direct signature of the light waves which is in contrast as compared to the corresponding QWs of the said materials in the absence of photoexcitation. The classical equation of the DMR in the absence of any field has been obtained as a special case of the present analysis under certain limiting conditions and this is the indirect test of the generalized formalism. We have suggested an experimental method of determining the DMR in QWs of degenerate materials having arbitrary dispersion laws and our results find six applications in the field of quantum effect devices.","band structure; cadmium compounds; carrier mobility; diffusion; dispersion relations; gallium arsenide; gallium compounds; III-V semiconductors; indium compounds; mercury compounds; semiconductor quantum wires; ternary semiconductors","en","journal article","American Institute of Physics","","","","","","","","Aerospace Engineering","Aerospace Materials & Manufacturing","","","",""
"uuid:236b5e62-408a-4612-b8e4-7a69043e3a25","http://resolver.tudelft.nl/uuid:236b5e62-408a-4612-b8e4-7a69043e3a25","Thermoelectric power in carbon nanotubes and quantum wires of nonlinear optical, optoelectronic, and related materials under strong magnetic field: Simplified theory and relative comparison","Ghatak, K.P.; Bhattacharya, S.; Bhowmik, S.; Benedictus, R.; Choudhury, S.","","2008","We study thermoelectric power under strong magnetic field (TPM) in carbon nanotubes (CNTs) and quantum wires (QWs) of nonlinear optical, optoelectronic, and related materials. The corresponding results for QWs of III-V, ternary, and quaternary compounds form a special case of our generalized analysis. The TPM has also been investigated in QWs of II-VI, IV-VI, stressed materials, n-GaP, p-PtSb2, n-GaSb, and bismuth on the basis of the appropriate carrier dispersion laws in the respective cases. It has been found, taking QWs of n-CdGeAs2, n-Cd3As2, n-InAs, n-InSb, n-GaAs, n-Hg1?xCdxTe, n-In1?xGaxAsyP1?y lattice-matched to InP, p-CdS, n-PbTe, n-PbSnTe, n-Pb1?xSnxSe, stressed n-InSb, n-GaP, p-PtSb2, n-GaSb, and bismuth as examples, that the respective TPM in the QWs of the aforementioned materials exhibits increasing quantum steps with the decreasing electron statistics with different numerical values, and the nature of the variations are totally band-structure-dependent. In CNTs, the TPM exhibits periodic oscillations with decreasing amplitudes for increasing electron statistics, and its nature is radically different as compared with the corresponding TPM of QWs since they depend exclusively on the respective band structures emphasizing the different signatures of the two entirely different one-dimensional nanostructured systems in various cases. The well-known expression of the TPM for wide gap materials has been obtained as a special case under certain limiting conditions, and this compatibility is an indirect test for our generalized formalism. In addition, we have suggested the experimental methods of determining the Einstein relation for the diffusivity-mobility ratio and the carrier contribution to the elastic constants for materials having arbitrary dispersion laws.","band structure; cadmium compounds; carbon nanotubes; gallium arsenide; gallium compounds; germanium compounds; III-V semiconductors; II-VI semiconductors; indium compounds; IV-VI semiconductors; lead compounds; mercury compounds; nonlinear optics; platinum compounds; semiconductor quantum wires; ternary semiconductors; thermoelectric power; tin compounds","en","journal article","American Institute of Physics","","","","","","","","Aerospace Engineering","Aerospace Materials & Manufacturing","","","",""
"uuid:e7c687d2-117a-4d16-84e8-f7c9006317ea","http://resolver.tudelft.nl/uuid:e7c687d2-117a-4d16-84e8-f7c9006317ea","Solid State Amorphisation - Thermodynamics and Kinetics","Benedictus, R.","Mittemeijer, E.J. (promotor)","1997","","","en","doctoral thesis","","","","","","","","","Mechanical Maritime and Materials Engineering","","","","",""
"uuid:530ae038-ecc0-4d49-95bb-a6f0c3edce25","http://resolver.tudelft.nl/uuid:530ae038-ecc0-4d49-95bb-a6f0c3edce25","Thermodynamic model for solid-state amorphization in binary systems at interfaces and grain boundaries","Benedictus, R.; Böttger, A.; Mittemeijer, E.J.","","1996","","","en","journal article","American Physical Society","","","","","","","","","","","","",""