CK
C. Kassapoglou
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40 records found
1
This work presents an analytical micromechanical framework to predict the in-plane shear behaviour of unidirectional composite plies. A fiber-matrix representative volume element (RVE) is formulated by modelling the fiber as a Timoshenko beam on an elastic foundation representing the matrix. From the governing boundary value problem, the effective RVE shear stiffness and shear modulus are derived and evaluated. The formulation is assessed through comparison with classical bounds and finite-element analyses for different fiber volume fractions and RVE geometries. To account for variability in fiber volume fraction, a statistical homogenisation procedure based on a power-mean representation is introduced, enabling correction of the initial stiffness predictions. The full framework, incorporating constituent failure, matrix nonlinearity, and local stiffness degradation, reproduces key features of the ply shear stress–strain response. While the framework captures the qualitative mechanisms governing the response, further independent characterisation of matrix behaviour and failure statistics is required to calibrate the model for quantitative prediction.
...
This work presents an analytical micromechanical framework to predict the in-plane shear behaviour of unidirectional composite plies. A fiber-matrix representative volume element (RVE) is formulated by modelling the fiber as a Timoshenko beam on an elastic foundation representing the matrix. From the governing boundary value problem, the effective RVE shear stiffness and shear modulus are derived and evaluated. The formulation is assessed through comparison with classical bounds and finite-element analyses for different fiber volume fractions and RVE geometries. To account for variability in fiber volume fraction, a statistical homogenisation procedure based on a power-mean representation is introduced, enabling correction of the initial stiffness predictions. The full framework, incorporating constituent failure, matrix nonlinearity, and local stiffness degradation, reproduces key features of the ply shear stress–strain response. While the framework captures the qualitative mechanisms governing the response, further independent characterisation of matrix behaviour and failure statistics is required to calibrate the model for quantitative prediction.
Damage Characterization and Modelling of Composite Plates Subjected to High-Speed Oblique Impacts
Developing a Robust Simulation Methodology
Simulating high-speed oblique impacts on composites remains a critical engineering challenge, as the monolithic shell models preferred in the industry often fail to accurately reproduce the diverse failure mechanisms typical of composite materials, such as fibre failure and delamination, whose interplay with inertial effects is essential for an accurate modeling of the event. To address this, a discretized modeling approach was developed with the explicit finite element software LS-Dyna, representing a composite laminate as a stack of shell elements connected via tiebreak contacts to allow for inter-laminar failure via a purely strength-based criterion. Validation against experimental data revealed that the plate response was governed by the mutual interaction of delamination, inter-ply friction and impactor kinematics. Using maximum out-of-plane intrusion as a benchmark, the newly developed model showed a discrepancy with the test data of -2.9%, against the +17.7% of the monolithic model baseline provided by the company at the beginning of the project. Furthermore, great qualitative correlation has been observed w.r.t. the delamination morphology when compared with C-scans of the tested samples. This study demonstrates that high-fidelity prediction of both intrusion and delamination shape and size in the proposed high-speed oblique impact event can be obtained through a strength-based discretized framework without the need for complex energy parameters or computationally expensive solid elements, offering a robust and efficient solution for industrial safety analysis.
...
Simulating high-speed oblique impacts on composites remains a critical engineering challenge, as the monolithic shell models preferred in the industry often fail to accurately reproduce the diverse failure mechanisms typical of composite materials, such as fibre failure and delamination, whose interplay with inertial effects is essential for an accurate modeling of the event. To address this, a discretized modeling approach was developed with the explicit finite element software LS-Dyna, representing a composite laminate as a stack of shell elements connected via tiebreak contacts to allow for inter-laminar failure via a purely strength-based criterion. Validation against experimental data revealed that the plate response was governed by the mutual interaction of delamination, inter-ply friction and impactor kinematics. Using maximum out-of-plane intrusion as a benchmark, the newly developed model showed a discrepancy with the test data of -2.9%, against the +17.7% of the monolithic model baseline provided by the company at the beginning of the project. Furthermore, great qualitative correlation has been observed w.r.t. the delamination morphology when compared with C-scans of the tested samples. This study demonstrates that high-fidelity prediction of both intrusion and delamination shape and size in the proposed high-speed oblique impact event can be obtained through a strength-based discretized framework without the need for complex energy parameters or computationally expensive solid elements, offering a robust and efficient solution for industrial safety analysis.
Gaps and Overlaps in Automated Fiber Placement Composites
Causes, Prediction and Process Design
Manufacturing variations in the automated fiber placement (AFP) process are one of the causes of gaps and overlaps. These manufacturing variations can be due to robot inaccuracy, tow lateral movement on the roller, tow width variation or tow compaction. An experimental setup was built to measure and investigate these various sources of manufacturing variations and their relative contributions to gap and overlap defects. This setup consisted of a commercial AFP head instrumented with additional sensors. Among all the measured sources of variations, lateral movement of the tow on the compaction roller was the biggest contributor to gaps and overlaps. The distributions of these sources of variations were fit with probability density functions. Random samples from these fits were used to simulate adjacent tows and predict the occurrence of gap and overlap defects. The distribution of predicted gaps correlated closely with the distribution of experimentally measured gaps. Thus, this approach of using statistical information about the sources of manufacturing variations to predict the frequency and magnitude of defects in a layup was validated.
Gap and overlap defects are formed during automated fiber placement (AFP) layup due to stochastic variations in tow position and geometry from the aforementioned sources. There is utility in predicting the size and frequency of these defects since they affect the manufacturing rate and structural performance. Two methods which reflect the measured process variability were implemented to simulate realistic tow geometry. A Monte Carlo (MC) simulation used independent random sampling from the distributions of the sources of variation. A Markov Chain Monte Carlo (MCMC) simulation used the Random Walk Metropolis algorithm which samples these distributions while considering the neighborhood of past samples thus preserving spatial continuity. Simulated tows were assembled into virtual laminae. Tow-level validation using spatial-frequency Fast Fourier Transform (FFT) analysis demonstrated that the MCMC method reproduces the dominant wavelengths and spectral characteristics of experimentally measured tow waviness, whereas the MC method introduces unrealistic high frequency variations. Lamina-level comparisons showed that while both methods predict similar gap and overlap area percentages, only the MCMC method accurately captures defect length distributions. The proposed framework provides realistic virtual layup geometries suitable for use in the modeling of the mesoscale aspects of AFP layups. The framework is also useful in determining optimal process parameters for manufacturing process design
Position variations are twice as effective as geometry variations in creating gap and overlaps defects. Tow lateral movement which is one of the causes of position variation was found to be a major contributor to gap and overlap defects during AFP layup in a straight line. In an experiment, to investigate this phenomenon under steering conditions, tow lateral movement was recorded during curvilinear AFP layup. This layup involved two different tow materials at steering radii varying from 1000 mm to 2000 mm. A shift of the tow in the radially outward direction of the curvilinear path was observed for both materials. The tows were observed to gradually shift to reach and stabilize at a position away from the roller center. The shift of the stabilized position was observed to become higher when the steering radius was reduced gradually from 2000 mm to 1000 mm. The rate of shift and the noise in the tow lateral movement differed for both materials. An analytical model was developed to predict and explain these tow lateral movement behaviors. A sensitivity analysis showed that the steering radius and the tow feed system chute geometry parameters had the most significant effect on the predicted tow shift magnitude while the coefficients of friction and compaction force parameters had the most significant effect on the predicted range of tow lateral movement. Further, the utility of the model predictions in offsetting the planned path to achieve layup trajectories with reduced gap and overlap defects was explained. ...
Gap and overlap defects are formed during automated fiber placement (AFP) layup due to stochastic variations in tow position and geometry from the aforementioned sources. There is utility in predicting the size and frequency of these defects since they affect the manufacturing rate and structural performance. Two methods which reflect the measured process variability were implemented to simulate realistic tow geometry. A Monte Carlo (MC) simulation used independent random sampling from the distributions of the sources of variation. A Markov Chain Monte Carlo (MCMC) simulation used the Random Walk Metropolis algorithm which samples these distributions while considering the neighborhood of past samples thus preserving spatial continuity. Simulated tows were assembled into virtual laminae. Tow-level validation using spatial-frequency Fast Fourier Transform (FFT) analysis demonstrated that the MCMC method reproduces the dominant wavelengths and spectral characteristics of experimentally measured tow waviness, whereas the MC method introduces unrealistic high frequency variations. Lamina-level comparisons showed that while both methods predict similar gap and overlap area percentages, only the MCMC method accurately captures defect length distributions. The proposed framework provides realistic virtual layup geometries suitable for use in the modeling of the mesoscale aspects of AFP layups. The framework is also useful in determining optimal process parameters for manufacturing process design
Position variations are twice as effective as geometry variations in creating gap and overlaps defects. Tow lateral movement which is one of the causes of position variation was found to be a major contributor to gap and overlap defects during AFP layup in a straight line. In an experiment, to investigate this phenomenon under steering conditions, tow lateral movement was recorded during curvilinear AFP layup. This layup involved two different tow materials at steering radii varying from 1000 mm to 2000 mm. A shift of the tow in the radially outward direction of the curvilinear path was observed for both materials. The tows were observed to gradually shift to reach and stabilize at a position away from the roller center. The shift of the stabilized position was observed to become higher when the steering radius was reduced gradually from 2000 mm to 1000 mm. The rate of shift and the noise in the tow lateral movement differed for both materials. An analytical model was developed to predict and explain these tow lateral movement behaviors. A sensitivity analysis showed that the steering radius and the tow feed system chute geometry parameters had the most significant effect on the predicted tow shift magnitude while the coefficients of friction and compaction force parameters had the most significant effect on the predicted range of tow lateral movement. Further, the utility of the model predictions in offsetting the planned path to achieve layup trajectories with reduced gap and overlap defects was explained. ...
Manufacturing variations in the automated fiber placement (AFP) process are one of the causes of gaps and overlaps. These manufacturing variations can be due to robot inaccuracy, tow lateral movement on the roller, tow width variation or tow compaction. An experimental setup was built to measure and investigate these various sources of manufacturing variations and their relative contributions to gap and overlap defects. This setup consisted of a commercial AFP head instrumented with additional sensors. Among all the measured sources of variations, lateral movement of the tow on the compaction roller was the biggest contributor to gaps and overlaps. The distributions of these sources of variations were fit with probability density functions. Random samples from these fits were used to simulate adjacent tows and predict the occurrence of gap and overlap defects. The distribution of predicted gaps correlated closely with the distribution of experimentally measured gaps. Thus, this approach of using statistical information about the sources of manufacturing variations to predict the frequency and magnitude of defects in a layup was validated.
Gap and overlap defects are formed during automated fiber placement (AFP) layup due to stochastic variations in tow position and geometry from the aforementioned sources. There is utility in predicting the size and frequency of these defects since they affect the manufacturing rate and structural performance. Two methods which reflect the measured process variability were implemented to simulate realistic tow geometry. A Monte Carlo (MC) simulation used independent random sampling from the distributions of the sources of variation. A Markov Chain Monte Carlo (MCMC) simulation used the Random Walk Metropolis algorithm which samples these distributions while considering the neighborhood of past samples thus preserving spatial continuity. Simulated tows were assembled into virtual laminae. Tow-level validation using spatial-frequency Fast Fourier Transform (FFT) analysis demonstrated that the MCMC method reproduces the dominant wavelengths and spectral characteristics of experimentally measured tow waviness, whereas the MC method introduces unrealistic high frequency variations. Lamina-level comparisons showed that while both methods predict similar gap and overlap area percentages, only the MCMC method accurately captures defect length distributions. The proposed framework provides realistic virtual layup geometries suitable for use in the modeling of the mesoscale aspects of AFP layups. The framework is also useful in determining optimal process parameters for manufacturing process design
Position variations are twice as effective as geometry variations in creating gap and overlaps defects. Tow lateral movement which is one of the causes of position variation was found to be a major contributor to gap and overlap defects during AFP layup in a straight line. In an experiment, to investigate this phenomenon under steering conditions, tow lateral movement was recorded during curvilinear AFP layup. This layup involved two different tow materials at steering radii varying from 1000 mm to 2000 mm. A shift of the tow in the radially outward direction of the curvilinear path was observed for both materials. The tows were observed to gradually shift to reach and stabilize at a position away from the roller center. The shift of the stabilized position was observed to become higher when the steering radius was reduced gradually from 2000 mm to 1000 mm. The rate of shift and the noise in the tow lateral movement differed for both materials. An analytical model was developed to predict and explain these tow lateral movement behaviors. A sensitivity analysis showed that the steering radius and the tow feed system chute geometry parameters had the most significant effect on the predicted tow shift magnitude while the coefficients of friction and compaction force parameters had the most significant effect on the predicted range of tow lateral movement. Further, the utility of the model predictions in offsetting the planned path to achieve layup trajectories with reduced gap and overlap defects was explained.
Gap and overlap defects are formed during automated fiber placement (AFP) layup due to stochastic variations in tow position and geometry from the aforementioned sources. There is utility in predicting the size and frequency of these defects since they affect the manufacturing rate and structural performance. Two methods which reflect the measured process variability were implemented to simulate realistic tow geometry. A Monte Carlo (MC) simulation used independent random sampling from the distributions of the sources of variation. A Markov Chain Monte Carlo (MCMC) simulation used the Random Walk Metropolis algorithm which samples these distributions while considering the neighborhood of past samples thus preserving spatial continuity. Simulated tows were assembled into virtual laminae. Tow-level validation using spatial-frequency Fast Fourier Transform (FFT) analysis demonstrated that the MCMC method reproduces the dominant wavelengths and spectral characteristics of experimentally measured tow waviness, whereas the MC method introduces unrealistic high frequency variations. Lamina-level comparisons showed that while both methods predict similar gap and overlap area percentages, only the MCMC method accurately captures defect length distributions. The proposed framework provides realistic virtual layup geometries suitable for use in the modeling of the mesoscale aspects of AFP layups. The framework is also useful in determining optimal process parameters for manufacturing process design
Position variations are twice as effective as geometry variations in creating gap and overlaps defects. Tow lateral movement which is one of the causes of position variation was found to be a major contributor to gap and overlap defects during AFP layup in a straight line. In an experiment, to investigate this phenomenon under steering conditions, tow lateral movement was recorded during curvilinear AFP layup. This layup involved two different tow materials at steering radii varying from 1000 mm to 2000 mm. A shift of the tow in the radially outward direction of the curvilinear path was observed for both materials. The tows were observed to gradually shift to reach and stabilize at a position away from the roller center. The shift of the stabilized position was observed to become higher when the steering radius was reduced gradually from 2000 mm to 1000 mm. The rate of shift and the noise in the tow lateral movement differed for both materials. An analytical model was developed to predict and explain these tow lateral movement behaviors. A sensitivity analysis showed that the steering radius and the tow feed system chute geometry parameters had the most significant effect on the predicted tow shift magnitude while the coefficients of friction and compaction force parameters had the most significant effect on the predicted range of tow lateral movement. Further, the utility of the model predictions in offsetting the planned path to achieve layup trajectories with reduced gap and overlap defects was explained.
The increased use of adhesively bonded joints in aerospace structures has given rise to ample research opportunities on the topic of ensuring structural integrity. One such method of verifying bond strength is through the use of non-destructive testing methods. One particular defect type, kissing bonds or zero-volume bonds, is notoriously difficult to detect using traditional techniques such as ultrasonic C-Scan. This thesis explores the feasibility of using Acoustic Emission (AE) monitoring to detect defects and characterize failure modes for adhesively bonded composite joints. Numerous Double Cantilever Beam (DCB) specimens containing various defect types were manufactured and tested under static Mode I loading conditions. Defect types included were pristine specimens, inclusion defects and artificial kissing bonds replicated through contamination of the adherend surface using release agent. Mechanical testing revealed that bondline defects significantly reduce the effective fracture toughness Gef f of defective specimens and induced alternative failure modes instead of complete cohesive failure. Most notably, specimens contaminated with release agent showed adhesion failure consistent with kissing bond type defects, while remaining undetectable when using conventional ultrasonic C-Scan inspection. AE monitoring allowed for identification of signal characteristics corresponding to cohesive failure, delamination and adhesion failure caused by kissing bonds and other defect types. Clustering of acoustic signals revealed characteristic frequency bands for certain defect types and failure modes. In particular, a cluster of signals of 130 [kHz] and 170 [kHz] peak frequency respectively could be correlated to delamination and cohesive failure. Wavelet transforms of the measured signals further revealed the broad frequency spectrum present in all specimen types. However, inconsistencies in the characteristic failure modes attributed to certain frequency bands make this mode of identification insufficient in its current state to detect failure modes with complete certainty.
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The increased use of adhesively bonded joints in aerospace structures has given rise to ample research opportunities on the topic of ensuring structural integrity. One such method of verifying bond strength is through the use of non-destructive testing methods. One particular defect type, kissing bonds or zero-volume bonds, is notoriously difficult to detect using traditional techniques such as ultrasonic C-Scan. This thesis explores the feasibility of using Acoustic Emission (AE) monitoring to detect defects and characterize failure modes for adhesively bonded composite joints. Numerous Double Cantilever Beam (DCB) specimens containing various defect types were manufactured and tested under static Mode I loading conditions. Defect types included were pristine specimens, inclusion defects and artificial kissing bonds replicated through contamination of the adherend surface using release agent. Mechanical testing revealed that bondline defects significantly reduce the effective fracture toughness Gef f of defective specimens and induced alternative failure modes instead of complete cohesive failure. Most notably, specimens contaminated with release agent showed adhesion failure consistent with kissing bond type defects, while remaining undetectable when using conventional ultrasonic C-Scan inspection. AE monitoring allowed for identification of signal characteristics corresponding to cohesive failure, delamination and adhesion failure caused by kissing bonds and other defect types. Clustering of acoustic signals revealed characteristic frequency bands for certain defect types and failure modes. In particular, a cluster of signals of 130 [kHz] and 170 [kHz] peak frequency respectively could be correlated to delamination and cohesive failure. Wavelet transforms of the measured signals further revealed the broad frequency spectrum present in all specimen types. However, inconsistencies in the characteristic failure modes attributed to certain frequency bands make this mode of identification insufficient in its current state to detect failure modes with complete certainty.
The use of fiber-reinforced composite materials in marine applications is limited by uncertainty surrounding their long-term fatigue behavior and micro-damage tolerance. This thesis aims to present and validate an experimental framework to detect and classify mechanical micro-damage in unidirectional carbon-fiber composites using acoustic emission (AE) monitoring and X-ray micro-computed tomography (micro-CT). AE monitoring provides real-time insight into the evolution of internal damage by capturing elastic waves emitted during micro-structural failure events, while micro-CT offers high-resolution visualization of internal damage states before and after mechanical loading. A comprehensive analysis was conducted involving signal processing, (normalized) frequency spectrum characterization, and unsupervised machine learning to classify AE events by damage type. This classification was subsequently validated against micro-CT scans. Results challenge the common assumption that AE signals with dominant low-frequency contributions are reliably indicative of matrix cracking. The proposed AE framework, when validated with micro-CT, shows promise for enabling accurate in-situ damage monitoring of composite structures in offshore environments. This approach supports the broader adoption of composites by improving confidence and knowledge about their structural integrity over time.
...
The use of fiber-reinforced composite materials in marine applications is limited by uncertainty surrounding their long-term fatigue behavior and micro-damage tolerance. This thesis aims to present and validate an experimental framework to detect and classify mechanical micro-damage in unidirectional carbon-fiber composites using acoustic emission (AE) monitoring and X-ray micro-computed tomography (micro-CT). AE monitoring provides real-time insight into the evolution of internal damage by capturing elastic waves emitted during micro-structural failure events, while micro-CT offers high-resolution visualization of internal damage states before and after mechanical loading. A comprehensive analysis was conducted involving signal processing, (normalized) frequency spectrum characterization, and unsupervised machine learning to classify AE events by damage type. This classification was subsequently validated against micro-CT scans. Results challenge the common assumption that AE signals with dominant low-frequency contributions are reliably indicative of matrix cracking. The proposed AE framework, when validated with micro-CT, shows promise for enabling accurate in-situ damage monitoring of composite structures in offshore environments. This approach supports the broader adoption of composites by improving confidence and knowledge about their structural integrity over time.
Master thesis
(2025)
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V. Carino, C. Kassapoglou, N.P.M. Werter, Michal Skarka, J.A. Pascoe, S. Giovani Pereira Castro
Sandwich structures are widely used in lightweight engineering applications due to their high stiffness-to-weight ratio and good energy absorption capabilities. However, their behavior under highly localized and dynamic loads remains complex to model accurately. This thesis investigates the transient response of circular sandwich panels subjected to high-dynamic pressure waves. An analytical model based on classical plate theory and modal superposition was developed to predict the displacement evolution of the panel. An analytical method to predict delamination onset through an energy-based criterion was developed as well. The results were validated through comparison with experimental data. The comparison shows good agreement in terms of the overall de- flection shape and magnitude. The proposed model captures the essential physics with minimal computational cost and offers a foundation for design optimization of dynamic load-resistant sandwich components. Future developments may focus on incorporating progressive damage models, as well as higher-order plate theories to enhance the predictive capability of the present model.
...
Sandwich structures are widely used in lightweight engineering applications due to their high stiffness-to-weight ratio and good energy absorption capabilities. However, their behavior under highly localized and dynamic loads remains complex to model accurately. This thesis investigates the transient response of circular sandwich panels subjected to high-dynamic pressure waves. An analytical model based on classical plate theory and modal superposition was developed to predict the displacement evolution of the panel. An analytical method to predict delamination onset through an energy-based criterion was developed as well. The results were validated through comparison with experimental data. The comparison shows good agreement in terms of the overall de- flection shape and magnitude. The proposed model captures the essential physics with minimal computational cost and offers a foundation for design optimization of dynamic load-resistant sandwich components. Future developments may focus on incorporating progressive damage models, as well as higher-order plate theories to enhance the predictive capability of the present model.
Society increasingly demands that ships become more sustainable and quieter, given their significant share of global fuel consumption and green-house gas emissions. Fiber-reinforced composite marine propellers can contribute meaningfully to these goals. As a promising alternative to the conventional rigid metallic propellers, flexible composite propellers can offer improved underwater radiated noise (URN) and propulsion efficiency. Furthermore, manufacturing propellers from fibre-reinforced composite materials makes them lighter and reduces their electromagnetic signature.
Despite the significant potential of composite propellers for marine propulsion systems, uncertainties in their fatigue behaviour have so far hindered their wide-spread adoption. These uncertainties can arise from imperfections during the manufacturing process, operational conditions different than the ones considered in the design, coating deterioration leading to water ingress, impact events, and more. Such factors can have significant impact on the lifetime of the propeller, which is typically expected to endure billions of cycles. Structural health monitoring (SHM) has the potential to mitigate this issue by real-time recording and assessing the structural response and integrity of the propeller. Such an SHM system should neither affect the propeller performance nor its load-bearing capacity. In addition to providing insights into the current structural integrity of the propeller, an SHM system may also enable enhanced estimation of the remaining lifetime, thereby minimizing the risk of unexpected failures and downtime.
This thesis investigates the feasibility of developing composite marine propellers with an embedded SHM system based on piezoelectric sensors. These sensors are capable of performing strain monitoring (with application in load/response estimation) and acoustic emission monitoring (with application in damage identification). Three main topics have been studied; (i) the feasibility of measuring dynamic strains in the propeller blade using the embedded sensors, (ii) the effect of embedding piezoelectric sensors on the structural integrity, and (iii) the feasibility of measuring and assessing damage-induced acoustic emissions using the embedded sensors. An analysis framework has been proposed for the identification, classification, and localisation of acoustic emissions in thick composite structures…
...
Despite the significant potential of composite propellers for marine propulsion systems, uncertainties in their fatigue behaviour have so far hindered their wide-spread adoption. These uncertainties can arise from imperfections during the manufacturing process, operational conditions different than the ones considered in the design, coating deterioration leading to water ingress, impact events, and more. Such factors can have significant impact on the lifetime of the propeller, which is typically expected to endure billions of cycles. Structural health monitoring (SHM) has the potential to mitigate this issue by real-time recording and assessing the structural response and integrity of the propeller. Such an SHM system should neither affect the propeller performance nor its load-bearing capacity. In addition to providing insights into the current structural integrity of the propeller, an SHM system may also enable enhanced estimation of the remaining lifetime, thereby minimizing the risk of unexpected failures and downtime.
This thesis investigates the feasibility of developing composite marine propellers with an embedded SHM system based on piezoelectric sensors. These sensors are capable of performing strain monitoring (with application in load/response estimation) and acoustic emission monitoring (with application in damage identification). Three main topics have been studied; (i) the feasibility of measuring dynamic strains in the propeller blade using the embedded sensors, (ii) the effect of embedding piezoelectric sensors on the structural integrity, and (iii) the feasibility of measuring and assessing damage-induced acoustic emissions using the embedded sensors. An analysis framework has been proposed for the identification, classification, and localisation of acoustic emissions in thick composite structures…
...
Society increasingly demands that ships become more sustainable and quieter, given their significant share of global fuel consumption and green-house gas emissions. Fiber-reinforced composite marine propellers can contribute meaningfully to these goals. As a promising alternative to the conventional rigid metallic propellers, flexible composite propellers can offer improved underwater radiated noise (URN) and propulsion efficiency. Furthermore, manufacturing propellers from fibre-reinforced composite materials makes them lighter and reduces their electromagnetic signature.
Despite the significant potential of composite propellers for marine propulsion systems, uncertainties in their fatigue behaviour have so far hindered their wide-spread adoption. These uncertainties can arise from imperfections during the manufacturing process, operational conditions different than the ones considered in the design, coating deterioration leading to water ingress, impact events, and more. Such factors can have significant impact on the lifetime of the propeller, which is typically expected to endure billions of cycles. Structural health monitoring (SHM) has the potential to mitigate this issue by real-time recording and assessing the structural response and integrity of the propeller. Such an SHM system should neither affect the propeller performance nor its load-bearing capacity. In addition to providing insights into the current structural integrity of the propeller, an SHM system may also enable enhanced estimation of the remaining lifetime, thereby minimizing the risk of unexpected failures and downtime.
This thesis investigates the feasibility of developing composite marine propellers with an embedded SHM system based on piezoelectric sensors. These sensors are capable of performing strain monitoring (with application in load/response estimation) and acoustic emission monitoring (with application in damage identification). Three main topics have been studied; (i) the feasibility of measuring dynamic strains in the propeller blade using the embedded sensors, (ii) the effect of embedding piezoelectric sensors on the structural integrity, and (iii) the feasibility of measuring and assessing damage-induced acoustic emissions using the embedded sensors. An analysis framework has been proposed for the identification, classification, and localisation of acoustic emissions in thick composite structures…
Despite the significant potential of composite propellers for marine propulsion systems, uncertainties in their fatigue behaviour have so far hindered their wide-spread adoption. These uncertainties can arise from imperfections during the manufacturing process, operational conditions different than the ones considered in the design, coating deterioration leading to water ingress, impact events, and more. Such factors can have significant impact on the lifetime of the propeller, which is typically expected to endure billions of cycles. Structural health monitoring (SHM) has the potential to mitigate this issue by real-time recording and assessing the structural response and integrity of the propeller. Such an SHM system should neither affect the propeller performance nor its load-bearing capacity. In addition to providing insights into the current structural integrity of the propeller, an SHM system may also enable enhanced estimation of the remaining lifetime, thereby minimizing the risk of unexpected failures and downtime.
This thesis investigates the feasibility of developing composite marine propellers with an embedded SHM system based on piezoelectric sensors. These sensors are capable of performing strain monitoring (with application in load/response estimation) and acoustic emission monitoring (with application in damage identification). Three main topics have been studied; (i) the feasibility of measuring dynamic strains in the propeller blade using the embedded sensors, (ii) the effect of embedding piezoelectric sensors on the structural integrity, and (iii) the feasibility of measuring and assessing damage-induced acoustic emissions using the embedded sensors. An analysis framework has been proposed for the identification, classification, and localisation of acoustic emissions in thick composite structures…
Master thesis
(2023)
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J. Romarís Villanueva, C. Kassapoglou, S. Giovani Pereira Castro, R.C. Alderliesten
An analytical model for the onset and growth of delaminations induced by matrix cracks under static loading is proposed. The model introduces four distinct configurations of delaminations originating from crack tips, which are applicable to cross-ply and general symmetrical laminates subjected to tension or tension + shear.
The delamination onset method employs Kassapoglou & Socci’s analytical crack propagation model to describe matrix cracks within the laminate. This leads to closed-form expressions for the Strain Energy Release Rate associated with both crack propagation and the initiation of delaminations at crack tips. Both expressions are used to predict the delamination onset load and crack spacing. Predictions show excellent agreement with test results for cross-plies under
tension.
Regarding the delamination growth model, it assumes a constant distance between cracks during growth (crack saturation). Experimentally-obtained Mode II interlaminar fracture toughness equation and closed-form expressions for Strain Energy Release Rate for delamination growth are employed for predictions. The model overpredicts the initial delamination length but exhibits satisfactory agreement with test results for the delamination growth in cross-ply laminates under tension.
Combining all 3 models allows for a comprehensive prediction of crack propagation, delamination onset and delamination growth for general symmetrical laminates. This comprehensive approach enables the visualization of all relevant information in a single figure, providing a concise and informative representation of the damage processes. Moreover, the analytical model facilitates the construction of design curves to investigate delamination onset in detail. ...
The delamination onset method employs Kassapoglou & Socci’s analytical crack propagation model to describe matrix cracks within the laminate. This leads to closed-form expressions for the Strain Energy Release Rate associated with both crack propagation and the initiation of delaminations at crack tips. Both expressions are used to predict the delamination onset load and crack spacing. Predictions show excellent agreement with test results for cross-plies under
tension.
Regarding the delamination growth model, it assumes a constant distance between cracks during growth (crack saturation). Experimentally-obtained Mode II interlaminar fracture toughness equation and closed-form expressions for Strain Energy Release Rate for delamination growth are employed for predictions. The model overpredicts the initial delamination length but exhibits satisfactory agreement with test results for the delamination growth in cross-ply laminates under tension.
Combining all 3 models allows for a comprehensive prediction of crack propagation, delamination onset and delamination growth for general symmetrical laminates. This comprehensive approach enables the visualization of all relevant information in a single figure, providing a concise and informative representation of the damage processes. Moreover, the analytical model facilitates the construction of design curves to investigate delamination onset in detail. ...
An analytical model for the onset and growth of delaminations induced by matrix cracks under static loading is proposed. The model introduces four distinct configurations of delaminations originating from crack tips, which are applicable to cross-ply and general symmetrical laminates subjected to tension or tension + shear.
The delamination onset method employs Kassapoglou & Socci’s analytical crack propagation model to describe matrix cracks within the laminate. This leads to closed-form expressions for the Strain Energy Release Rate associated with both crack propagation and the initiation of delaminations at crack tips. Both expressions are used to predict the delamination onset load and crack spacing. Predictions show excellent agreement with test results for cross-plies under
tension.
Regarding the delamination growth model, it assumes a constant distance between cracks during growth (crack saturation). Experimentally-obtained Mode II interlaminar fracture toughness equation and closed-form expressions for Strain Energy Release Rate for delamination growth are employed for predictions. The model overpredicts the initial delamination length but exhibits satisfactory agreement with test results for the delamination growth in cross-ply laminates under tension.
Combining all 3 models allows for a comprehensive prediction of crack propagation, delamination onset and delamination growth for general symmetrical laminates. This comprehensive approach enables the visualization of all relevant information in a single figure, providing a concise and informative representation of the damage processes. Moreover, the analytical model facilitates the construction of design curves to investigate delamination onset in detail.
The delamination onset method employs Kassapoglou & Socci’s analytical crack propagation model to describe matrix cracks within the laminate. This leads to closed-form expressions for the Strain Energy Release Rate associated with both crack propagation and the initiation of delaminations at crack tips. Both expressions are used to predict the delamination onset load and crack spacing. Predictions show excellent agreement with test results for cross-plies under
tension.
Regarding the delamination growth model, it assumes a constant distance between cracks during growth (crack saturation). Experimentally-obtained Mode II interlaminar fracture toughness equation and closed-form expressions for Strain Energy Release Rate for delamination growth are employed for predictions. The model overpredicts the initial delamination length but exhibits satisfactory agreement with test results for the delamination growth in cross-ply laminates under tension.
Combining all 3 models allows for a comprehensive prediction of crack propagation, delamination onset and delamination growth for general symmetrical laminates. This comprehensive approach enables the visualization of all relevant information in a single figure, providing a concise and informative representation of the damage processes. Moreover, the analytical model facilitates the construction of design curves to investigate delamination onset in detail.
Master thesis
(2023)
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T. van Herwerden, C. Kassapoglou, Pooria L. Pahlavan, A.J. Huijer, J.H. den Besten
Fiber reinforced composites have been increasingly used in the aerospace and automotive industry, due to their potential advantages for designing flexible, strong and lightweight structures. More recently they are also being considered for the manufacturing of marine propellers. Since they have the potential to lower the weight, lower the maintenance costs, increase the efficiency at off-design conditions, improve cavitation inception speed and minimize acoustic signatures. Exploiting the full potential of composite propellers however requires that they need to be cost-effective and to do so it is required that the lifetime of the blade is sufficient. To determine the lifetime of the blade it is
crucial to determine how the composite blade will respond to a wide variety of environmental and loading conditions that it will experience over its life. Basically one needs to determine what effects fatigue will have on the material properties of the blade. The main objective of this thesis is to estimate the fatigue lifetime of composite marine propellers subjected to a pressure distribution determined by a Fluid-Structure Interaction
(FSI)model with the use of a progressive damage model integrated into a Finite
Element Model (FEM). The fluid structure interaction model to determine the pressure distribution has already been created Maljaars (2019). Currently the mostly used and most reliable approach is to use an experimental approach in order to estimate the fatigue life. However, for custom designs such as marine propellers this is a long and costly process. Modelling fatigue the fatigue performance in an earlier stage of the design cycle will result in significant cost and time savings.
The expected fatigue lifetime of the composite marine propeller is concluded to be at least 1012 cycles under the considered loading condition. If the propeller would rotate at 600 rpm for 24 hours per day this would translate to over 3000 years. The reason behind this large number is that the combination of the applied pressure load and the strength of the carbon fiber propeller is such that the stresses in each ply are very low. These low stresses create almost no damage throughout the propeller blade even for ultra high cycles. ...
crucial to determine how the composite blade will respond to a wide variety of environmental and loading conditions that it will experience over its life. Basically one needs to determine what effects fatigue will have on the material properties of the blade. The main objective of this thesis is to estimate the fatigue lifetime of composite marine propellers subjected to a pressure distribution determined by a Fluid-Structure Interaction
(FSI)model with the use of a progressive damage model integrated into a Finite
Element Model (FEM). The fluid structure interaction model to determine the pressure distribution has already been created Maljaars (2019). Currently the mostly used and most reliable approach is to use an experimental approach in order to estimate the fatigue life. However, for custom designs such as marine propellers this is a long and costly process. Modelling fatigue the fatigue performance in an earlier stage of the design cycle will result in significant cost and time savings.
The expected fatigue lifetime of the composite marine propeller is concluded to be at least 1012 cycles under the considered loading condition. If the propeller would rotate at 600 rpm for 24 hours per day this would translate to over 3000 years. The reason behind this large number is that the combination of the applied pressure load and the strength of the carbon fiber propeller is such that the stresses in each ply are very low. These low stresses create almost no damage throughout the propeller blade even for ultra high cycles. ...
Fiber reinforced composites have been increasingly used in the aerospace and automotive industry, due to their potential advantages for designing flexible, strong and lightweight structures. More recently they are also being considered for the manufacturing of marine propellers. Since they have the potential to lower the weight, lower the maintenance costs, increase the efficiency at off-design conditions, improve cavitation inception speed and minimize acoustic signatures. Exploiting the full potential of composite propellers however requires that they need to be cost-effective and to do so it is required that the lifetime of the blade is sufficient. To determine the lifetime of the blade it is
crucial to determine how the composite blade will respond to a wide variety of environmental and loading conditions that it will experience over its life. Basically one needs to determine what effects fatigue will have on the material properties of the blade. The main objective of this thesis is to estimate the fatigue lifetime of composite marine propellers subjected to a pressure distribution determined by a Fluid-Structure Interaction
(FSI)model with the use of a progressive damage model integrated into a Finite
Element Model (FEM). The fluid structure interaction model to determine the pressure distribution has already been created Maljaars (2019). Currently the mostly used and most reliable approach is to use an experimental approach in order to estimate the fatigue life. However, for custom designs such as marine propellers this is a long and costly process. Modelling fatigue the fatigue performance in an earlier stage of the design cycle will result in significant cost and time savings.
The expected fatigue lifetime of the composite marine propeller is concluded to be at least 1012 cycles under the considered loading condition. If the propeller would rotate at 600 rpm for 24 hours per day this would translate to over 3000 years. The reason behind this large number is that the combination of the applied pressure load and the strength of the carbon fiber propeller is such that the stresses in each ply are very low. These low stresses create almost no damage throughout the propeller blade even for ultra high cycles.
crucial to determine how the composite blade will respond to a wide variety of environmental and loading conditions that it will experience over its life. Basically one needs to determine what effects fatigue will have on the material properties of the blade. The main objective of this thesis is to estimate the fatigue lifetime of composite marine propellers subjected to a pressure distribution determined by a Fluid-Structure Interaction
(FSI)model with the use of a progressive damage model integrated into a Finite
Element Model (FEM). The fluid structure interaction model to determine the pressure distribution has already been created Maljaars (2019). Currently the mostly used and most reliable approach is to use an experimental approach in order to estimate the fatigue life. However, for custom designs such as marine propellers this is a long and costly process. Modelling fatigue the fatigue performance in an earlier stage of the design cycle will result in significant cost and time savings.
The expected fatigue lifetime of the composite marine propeller is concluded to be at least 1012 cycles under the considered loading condition. If the propeller would rotate at 600 rpm for 24 hours per day this would translate to over 3000 years. The reason behind this large number is that the combination of the applied pressure load and the strength of the carbon fiber propeller is such that the stresses in each ply are very low. These low stresses create almost no damage throughout the propeller blade even for ultra high cycles.
Lugs are a specific type of joint with a semi-circular geometry around the pinhole utilized in the aerospace field. Its distinct geometry and ability to carry loads in its plane make it a very common choice for design engineers. Although this type of joint is widely used, there are no analytical equations that can predict the stresses around the hole. This research topic presents a semi-analytical approach to predict the in-plane stresses and failure modes of a composite lug under tensile pin loading. The methodology developed is based on stress functions for anisotropic beams implemented in stress equations for solid bodies in a polar coordinate system. The results of this approach are validated with the use of numerical simulation models, whose trustworthiness is verified by tensile tests. The outcome of this thesis is in-plane stress distribution graphs for every layer of the laminate around the hole and the in-plane failure mode of the lug. The results show a good accordance between the stresses predicted from the semi-analytical approach and the numerical simulations. Moreover, two lug designs with different geometric characteristics were tested in order to observe the influence of the geometry on the failure load. It was concluded that the geometry affects the maximum failure load but not the stress distribution, which is concurrent with the literature. Overall, the methodology presented in this research topic provided promising results. The findings of this thesis can have a great impact and aid engineers in estimating the stresses in a composite lug from the preliminary phase of a project.
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Lugs are a specific type of joint with a semi-circular geometry around the pinhole utilized in the aerospace field. Its distinct geometry and ability to carry loads in its plane make it a very common choice for design engineers. Although this type of joint is widely used, there are no analytical equations that can predict the stresses around the hole. This research topic presents a semi-analytical approach to predict the in-plane stresses and failure modes of a composite lug under tensile pin loading. The methodology developed is based on stress functions for anisotropic beams implemented in stress equations for solid bodies in a polar coordinate system. The results of this approach are validated with the use of numerical simulation models, whose trustworthiness is verified by tensile tests. The outcome of this thesis is in-plane stress distribution graphs for every layer of the laminate around the hole and the in-plane failure mode of the lug. The results show a good accordance between the stresses predicted from the semi-analytical approach and the numerical simulations. Moreover, two lug designs with different geometric characteristics were tested in order to observe the influence of the geometry on the failure load. It was concluded that the geometry affects the maximum failure load but not the stress distribution, which is concurrent with the literature. Overall, the methodology presented in this research topic provided promising results. The findings of this thesis can have a great impact and aid engineers in estimating the stresses in a composite lug from the preliminary phase of a project.
The use of Grid-stiffened structures has been increasing in the space industry over the last decade. Thanks to it is high specific mechanical properties and excellent damage tolerance characteristics, researchers also started looking into the potential of using them for aeronautical applications. However, not much has been done to investigate the reduction in strength after barely visible impact damage and visible impact damage, and how much energy is needed to cause such damage, which is an important requirement for aircraft certification. In this project, a grid-stiffened replica of an existing reference cargo drone is created, and the design is tested to check its compliance with the requirements. This involved modelling of the design, manufacturing of test coupons, impact and mechanical tests, and model validation. The results showed a possible weight reduction, with no major reduction in strength observed with impacting using the cut-off energy level set by the manufacturer.
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The use of Grid-stiffened structures has been increasing in the space industry over the last decade. Thanks to it is high specific mechanical properties and excellent damage tolerance characteristics, researchers also started looking into the potential of using them for aeronautical applications. However, not much has been done to investigate the reduction in strength after barely visible impact damage and visible impact damage, and how much energy is needed to cause such damage, which is an important requirement for aircraft certification. In this project, a grid-stiffened replica of an existing reference cargo drone is created, and the design is tested to check its compliance with the requirements. This involved modelling of the design, manufacturing of test coupons, impact and mechanical tests, and model validation. The results showed a possible weight reduction, with no major reduction in strength observed with impacting using the cut-off energy level set by the manufacturer.
A building block pyramid is designed used to evaluate a composite aircraft structure, combining tests and analyses, using stiffened panels, single-stringer specimens and coupons. Failure in these structures can be caused by postbuckling-induced skin-stringer separation, which is complex, involving matrix cracks, fibre bridges, and delamination migrations. Standardized tests covering postbuckling-induced skin-stringer separation are lacking. First, a material characterization is performed on the coupon level. These properties are applied to a stiffened panel model to identify critical postbuckling regions. Then a single-stringer specimen is designed that combines the material complexities of the coupon level and the geometrical complexities of the panel by mimicking the postbuckling shape. Specifically a seven-point bending configuration to study bending-induced separation and a four-point twisting configuration for skin twisting-induced separation. The guidelines for modelling and testing can assist in standardising these test methods.
Using composite materials in aircraft structures can reduce weight compared to conventional metals. However, utilizing more of the material's load-carrying capabilities can further reduce weight. ...
Using composite materials in aircraft structures can reduce weight compared to conventional metals. However, utilizing more of the material's load-carrying capabilities can further reduce weight. ...
A building block pyramid is designed used to evaluate a composite aircraft structure, combining tests and analyses, using stiffened panels, single-stringer specimens and coupons. Failure in these structures can be caused by postbuckling-induced skin-stringer separation, which is complex, involving matrix cracks, fibre bridges, and delamination migrations. Standardized tests covering postbuckling-induced skin-stringer separation are lacking. First, a material characterization is performed on the coupon level. These properties are applied to a stiffened panel model to identify critical postbuckling regions. Then a single-stringer specimen is designed that combines the material complexities of the coupon level and the geometrical complexities of the panel by mimicking the postbuckling shape. Specifically a seven-point bending configuration to study bending-induced separation and a four-point twisting configuration for skin twisting-induced separation. The guidelines for modelling and testing can assist in standardising these test methods.
Using composite materials in aircraft structures can reduce weight compared to conventional metals. However, utilizing more of the material's load-carrying capabilities can further reduce weight.
Using composite materials in aircraft structures can reduce weight compared to conventional metals. However, utilizing more of the material's load-carrying capabilities can further reduce weight.
Master thesis
(2022)
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M.G.A. Adams, L. Pahlavan, A.J. Huijer, C. Kassapoglou, C.L. Walters, André Vaders
Fiber Reinforced Composite (FRC) materials are gaining great popularity in marine structures because of their excellent strength-to-weight ratio, low density, and provided freedom in the design process. However, the use of FRC materials comes along with relatively large uncertainties in material properties and structural integrity after manufacturing and during its use. In this research a new in-situ non-destructive stiffness assessment methodology is proposed. This methodology is based on a coupling principle between the laminate structural stiffness properties and the ultrasonic guided wave characteristics of FRC materials. In the methodology, a range of possible stiffness properties is defined based on the structural information available for a structure of interest. The average relation between this stiffness range of interest and corresponding wave characteristics is described using a set of coupling coefficients which are determined using numerical simulations. For this, a batch of reference laminates is constructed that covers the entire stiffness range of interest. Input for the system are the group velocities of the zeroth-order symmetric and antisymmetric guided wave modes, measured on the structure of interest. The potential of the proposed methodology is evaluated using a numerical feasibility study based on numerical simulations. Good results were obtained for different test scenarios, varying in the amount of structural information available on the structure of interest. Thereafter, the in-situ application of the methodology has been examined in an experimental setup. Good measurement and analysis times were achieved by using a compact measuring device that is capable of recording the wave signal in five directions simultaneously. A reliable accuracy assessment of the in-situ application of the methodology was, however, difficult to obtain due to the lack of reliable reference studies. Therefore, in future research reliable reference information should be gathered. Additionally, a next step for future research should focus on decreasing the amount of information available on the structure of interest.
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Fiber Reinforced Composite (FRC) materials are gaining great popularity in marine structures because of their excellent strength-to-weight ratio, low density, and provided freedom in the design process. However, the use of FRC materials comes along with relatively large uncertainties in material properties and structural integrity after manufacturing and during its use. In this research a new in-situ non-destructive stiffness assessment methodology is proposed. This methodology is based on a coupling principle between the laminate structural stiffness properties and the ultrasonic guided wave characteristics of FRC materials. In the methodology, a range of possible stiffness properties is defined based on the structural information available for a structure of interest. The average relation between this stiffness range of interest and corresponding wave characteristics is described using a set of coupling coefficients which are determined using numerical simulations. For this, a batch of reference laminates is constructed that covers the entire stiffness range of interest. Input for the system are the group velocities of the zeroth-order symmetric and antisymmetric guided wave modes, measured on the structure of interest. The potential of the proposed methodology is evaluated using a numerical feasibility study based on numerical simulations. Good results were obtained for different test scenarios, varying in the amount of structural information available on the structure of interest. Thereafter, the in-situ application of the methodology has been examined in an experimental setup. Good measurement and analysis times were achieved by using a compact measuring device that is capable of recording the wave signal in five directions simultaneously. A reliable accuracy assessment of the in-situ application of the methodology was, however, difficult to obtain due to the lack of reliable reference studies. Therefore, in future research reliable reference information should be gathered. Additionally, a next step for future research should focus on decreasing the amount of information available on the structure of interest.
This study is an attempt to develop a preliminary composite fuselage sizing tool for the decision making process utilizing analytical structural analysis equations and a bottom-up cost approach to estimate weight and cost. Previous research by several authors and companies is reviewed in order to define the knowledge gaps that the project is going to fill. The objectives of this project are divided into two directions. The first one is the weight and cost fuselage design, and the second, is the weight and cost optimization process. After examining the existing literature both from academia and industry a different approach is proposed for each sector. In the structural design an analytical based model is proposed to assess the components integrity while cost equations for fully learned manufacturing processes are used based on the Advanced Composites Cost Estimation Manual (ACCEM). An experience-driven optimization algorithm is proposed afterwards, taking into account manufacturing considerations and design rules of thumb. By combining these tools, a general tool for fuselage design that is completely suited for the preliminary design phase is proposed. Τhe trade-off studies can provide important knowledge on the effect of different decisions and establish new design guidelines. The study concludes that an increase of the number of stiffeners and frames, in a fuselage structure, leads to a general decrease in weight and an increase in manufacturing cost. The addition of more stringers or frames after a certain level leads to an increase in weight, while the cost follows the same trend. The manufacturing constraints and the design rules-of-thumb applied lead to an increase in structural weight. Finally, the comparison between skin-stiffened and sandwich designs, shows that the weight saving potential is comparable for both configurations, and the cost saving potential is higher for the sandwich design.
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This study is an attempt to develop a preliminary composite fuselage sizing tool for the decision making process utilizing analytical structural analysis equations and a bottom-up cost approach to estimate weight and cost. Previous research by several authors and companies is reviewed in order to define the knowledge gaps that the project is going to fill. The objectives of this project are divided into two directions. The first one is the weight and cost fuselage design, and the second, is the weight and cost optimization process. After examining the existing literature both from academia and industry a different approach is proposed for each sector. In the structural design an analytical based model is proposed to assess the components integrity while cost equations for fully learned manufacturing processes are used based on the Advanced Composites Cost Estimation Manual (ACCEM). An experience-driven optimization algorithm is proposed afterwards, taking into account manufacturing considerations and design rules of thumb. By combining these tools, a general tool for fuselage design that is completely suited for the preliminary design phase is proposed. Τhe trade-off studies can provide important knowledge on the effect of different decisions and establish new design guidelines. The study concludes that an increase of the number of stiffeners and frames, in a fuselage structure, leads to a general decrease in weight and an increase in manufacturing cost. The addition of more stringers or frames after a certain level leads to an increase in weight, while the cost follows the same trend. The manufacturing constraints and the design rules-of-thumb applied lead to an increase in structural weight. Finally, the comparison between skin-stiffened and sandwich designs, shows that the weight saving potential is comparable for both configurations, and the cost saving potential is higher for the sandwich design.
Sustainable and circular retrofitting facade
"A future proof panel for building renovation"
Master thesis
(2021)
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R. Nuñez Larios, H.R. Schipper, M. Ottele, T. Konstantinou, C. Kassapoglou, Carlos Klein, Arjan de Haan
The Paris agreement’s mechanisms for 2050 represent a challenge for the world to achieve Net-zero emission and climate resilience. Retrofitting the existing stock is a critical step in every nation to achieve these goals. The building sector has a significant role in the Net-zero emission transition. The ambitions for retrofitting the Netherlands´ by 2030 and 2050 bring the need to explore new products taking sustainability and circular economy as the basis of design. This research explores the application of a “cradle to cradle” design approach to redesign a sandwich panel currently used as a renovation strategy to wrap existing dwellings in The Netherlands. The research in performed from the perspective of a façade company in the national market.
The current product manufactured by the company is not studied with the end of its service life in mind and is designed mainly with fossil fuels related products. Also, the time component is detached from the product, and scenarios where the materials are “processed and disposed” or “mined and reused” are not considered. The research explores three different façade concepts that contrast with a traditional linear production based mainly on fossil fuels. The analysis brings a set of 24 options, each with three circularity scenarios. The conclusions reveal that the environmental impacts and success of a “cradle to cradle” design strategy has a close relationship with the number of years the existing dwellings will be used. By reusing the existing dwellings for prolonged times (50 and 100 years), the best option for the company is to develop a biobased sandwich panel relying on renewables and materials with low environmental impacts but as an efficient “cradle to grave” strategy. However, for a shorter span of usage in the existing stock (25 years), the best option is a “cradle to cradle” strategy where the resources are taken back to the technical cycle combined with reduced usage of materials for the cladding system.
Some of the technical recommendations suggested are to test the biobased panel for a mechanical test. Afterward, develop the construction details for connections in foundation, windows, and doors to finally build a 1:1 mock-up to be tested for meteorological degradations and durability. Also, further analysis is needed for a financial case for the scenarios where materials are used after a first cycle. Finally, further research is needed to develop fully biobased matrixes to biocomposite fully biodegradable, allowing them to get back into a biological cycle. ...
The current product manufactured by the company is not studied with the end of its service life in mind and is designed mainly with fossil fuels related products. Also, the time component is detached from the product, and scenarios where the materials are “processed and disposed” or “mined and reused” are not considered. The research explores three different façade concepts that contrast with a traditional linear production based mainly on fossil fuels. The analysis brings a set of 24 options, each with three circularity scenarios. The conclusions reveal that the environmental impacts and success of a “cradle to cradle” design strategy has a close relationship with the number of years the existing dwellings will be used. By reusing the existing dwellings for prolonged times (50 and 100 years), the best option for the company is to develop a biobased sandwich panel relying on renewables and materials with low environmental impacts but as an efficient “cradle to grave” strategy. However, for a shorter span of usage in the existing stock (25 years), the best option is a “cradle to cradle” strategy where the resources are taken back to the technical cycle combined with reduced usage of materials for the cladding system.
Some of the technical recommendations suggested are to test the biobased panel for a mechanical test. Afterward, develop the construction details for connections in foundation, windows, and doors to finally build a 1:1 mock-up to be tested for meteorological degradations and durability. Also, further analysis is needed for a financial case for the scenarios where materials are used after a first cycle. Finally, further research is needed to develop fully biobased matrixes to biocomposite fully biodegradable, allowing them to get back into a biological cycle. ...
The Paris agreement’s mechanisms for 2050 represent a challenge for the world to achieve Net-zero emission and climate resilience. Retrofitting the existing stock is a critical step in every nation to achieve these goals. The building sector has a significant role in the Net-zero emission transition. The ambitions for retrofitting the Netherlands´ by 2030 and 2050 bring the need to explore new products taking sustainability and circular economy as the basis of design. This research explores the application of a “cradle to cradle” design approach to redesign a sandwich panel currently used as a renovation strategy to wrap existing dwellings in The Netherlands. The research in performed from the perspective of a façade company in the national market.
The current product manufactured by the company is not studied with the end of its service life in mind and is designed mainly with fossil fuels related products. Also, the time component is detached from the product, and scenarios where the materials are “processed and disposed” or “mined and reused” are not considered. The research explores three different façade concepts that contrast with a traditional linear production based mainly on fossil fuels. The analysis brings a set of 24 options, each with three circularity scenarios. The conclusions reveal that the environmental impacts and success of a “cradle to cradle” design strategy has a close relationship with the number of years the existing dwellings will be used. By reusing the existing dwellings for prolonged times (50 and 100 years), the best option for the company is to develop a biobased sandwich panel relying on renewables and materials with low environmental impacts but as an efficient “cradle to grave” strategy. However, for a shorter span of usage in the existing stock (25 years), the best option is a “cradle to cradle” strategy where the resources are taken back to the technical cycle combined with reduced usage of materials for the cladding system.
Some of the technical recommendations suggested are to test the biobased panel for a mechanical test. Afterward, develop the construction details for connections in foundation, windows, and doors to finally build a 1:1 mock-up to be tested for meteorological degradations and durability. Also, further analysis is needed for a financial case for the scenarios where materials are used after a first cycle. Finally, further research is needed to develop fully biobased matrixes to biocomposite fully biodegradable, allowing them to get back into a biological cycle.
The current product manufactured by the company is not studied with the end of its service life in mind and is designed mainly with fossil fuels related products. Also, the time component is detached from the product, and scenarios where the materials are “processed and disposed” or “mined and reused” are not considered. The research explores three different façade concepts that contrast with a traditional linear production based mainly on fossil fuels. The analysis brings a set of 24 options, each with three circularity scenarios. The conclusions reveal that the environmental impacts and success of a “cradle to cradle” design strategy has a close relationship with the number of years the existing dwellings will be used. By reusing the existing dwellings for prolonged times (50 and 100 years), the best option for the company is to develop a biobased sandwich panel relying on renewables and materials with low environmental impacts but as an efficient “cradle to grave” strategy. However, for a shorter span of usage in the existing stock (25 years), the best option is a “cradle to cradle” strategy where the resources are taken back to the technical cycle combined with reduced usage of materials for the cladding system.
Some of the technical recommendations suggested are to test the biobased panel for a mechanical test. Afterward, develop the construction details for connections in foundation, windows, and doors to finally build a 1:1 mock-up to be tested for meteorological degradations and durability. Also, further analysis is needed for a financial case for the scenarios where materials are used after a first cycle. Finally, further research is needed to develop fully biobased matrixes to biocomposite fully biodegradable, allowing them to get back into a biological cycle.
Patching a Fuselage
Application of Straight Fiber Variable Stiffness Laminates in Large Aerospace Structures
Straight fiber variable stiffness laminates use multiple overlapping patches to tailor the fiber orientations in particular regions of the laminate. A novel, automated framework for the design of manufacturable laminate has been developed using different stages. In the first and second stage an optimal stiffness distribution is determined using lamination parameters and converted to stacking sequences on a per region basis. In the third and fourth stages cellular automata and network theory are used to introduce cohesion between regions and comply with current manufacturing standards. Plates in uniaxial compression and cylinders in bending show an increase in buckling performance of 42% and 30% respectively. Such improvements do allow weight savings between 7-11% for these types of structures. When the additional cost of manufacturing and the cost-to-weight ratio for airlines are considered, these laminates already have the potential to significantly reduce the cost of air travel.
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Straight fiber variable stiffness laminates use multiple overlapping patches to tailor the fiber orientations in particular regions of the laminate. A novel, automated framework for the design of manufacturable laminate has been developed using different stages. In the first and second stage an optimal stiffness distribution is determined using lamination parameters and converted to stacking sequences on a per region basis. In the third and fourth stages cellular automata and network theory are used to introduce cohesion between regions and comply with current manufacturing standards. Plates in uniaxial compression and cylinders in bending show an increase in buckling performance of 42% and 30% respectively. Such improvements do allow weight savings between 7-11% for these types of structures. When the additional cost of manufacturing and the cost-to-weight ratio for airlines are considered, these laminates already have the potential to significantly reduce the cost of air travel.
The COVID-19 pandemic had a significant impact on the aviation industry with more than 60% reduction in the passenger traffic in the year 2020 compared to year 2019. The passenger traffic which is now expected to reach the 2019 level only around the year 2024 will still continue to grow but at a lower pace compared to the pre pandemic levels. The environmental issues which were a major concern for the aviation industry before pandemic will still be relevant. The objective of achieving an environmentally friendly zero emission aircraft will not be met only with alternative fuels and propulsion concepts but also require advanced material technologies and novel designs. A promising technology having the potential to improve the performance of an aircraft by improving the structural efficiency is the application of aeroelastic tailoring with the help of composite materials. However, incorporating aeroelastic tailoring with composite materials in the design process is not a trivial task. In the traditional design process, knowledge about the design increases, while the design freedom decreases as one goes from conceptual to preliminary and finally to the detailed design. For conventional designs, the lack of knowledge during the initial stages is compensated through empirical knowledge. However, the lack of such empirical knowledge for novel design and advanced technology, results in the need for increased physics-based knowledge during the initial design process. In the research presented in this dissertation, the focus was on increasing knowledge in the early stages of the aeroelastic design process of a composite wing. As current state of art in aeroelastic tailoring does not include critical gust and fatigue loads, this thesis is focused on including critical gust loads and fatigue loading requirements in the preliminary aeroelastic optimization framework…
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The COVID-19 pandemic had a significant impact on the aviation industry with more than 60% reduction in the passenger traffic in the year 2020 compared to year 2019. The passenger traffic which is now expected to reach the 2019 level only around the year 2024 will still continue to grow but at a lower pace compared to the pre pandemic levels. The environmental issues which were a major concern for the aviation industry before pandemic will still be relevant. The objective of achieving an environmentally friendly zero emission aircraft will not be met only with alternative fuels and propulsion concepts but also require advanced material technologies and novel designs. A promising technology having the potential to improve the performance of an aircraft by improving the structural efficiency is the application of aeroelastic tailoring with the help of composite materials. However, incorporating aeroelastic tailoring with composite materials in the design process is not a trivial task. In the traditional design process, knowledge about the design increases, while the design freedom decreases as one goes from conceptual to preliminary and finally to the detailed design. For conventional designs, the lack of knowledge during the initial stages is compensated through empirical knowledge. However, the lack of such empirical knowledge for novel design and advanced technology, results in the need for increased physics-based knowledge during the initial design process. In the research presented in this dissertation, the focus was on increasing knowledge in the early stages of the aeroelastic design process of a composite wing. As current state of art in aeroelastic tailoring does not include critical gust and fatigue loads, this thesis is focused on including critical gust loads and fatigue loading requirements in the preliminary aeroelastic optimization framework…
Composite lattice structures (CLS) offer high performance and demonstrate significant mass savings in space structure applications. Local modifications of regular lattice designs have the potential to further improve the lattice performance. This research explored the micro-structural quality features of CLSs manufactured with pre-preg fibre-placement, and how quality is impacted by lattice modifications.
Modifications to a regular lattice for a representative case of an attachment point load are identified using a topology optimisation tool. Three lattice modifications techniques were identified: rib width variations, rib angle variations and additional ribs. A sample lattice with modifications was manufactured and evaluated by C-scan, CT techniques and micro-sections. An explanation of quality features in CLS is described and quantified using a presented characterisation model based on node transition waviness.
Using the presented explanation, a quantitative quality model was developed to relate lattice design geometry to manufactured quality for this process. The model was used to design and manufacture a second panel with improved implementation of lattice modifications. The quality model was improved and shown to explain more than 75% of all observed quality variation in the two panels with a linear regression. Future work and limitations the of the quality model are discussed. ...
Modifications to a regular lattice for a representative case of an attachment point load are identified using a topology optimisation tool. Three lattice modifications techniques were identified: rib width variations, rib angle variations and additional ribs. A sample lattice with modifications was manufactured and evaluated by C-scan, CT techniques and micro-sections. An explanation of quality features in CLS is described and quantified using a presented characterisation model based on node transition waviness.
Using the presented explanation, a quantitative quality model was developed to relate lattice design geometry to manufactured quality for this process. The model was used to design and manufacture a second panel with improved implementation of lattice modifications. The quality model was improved and shown to explain more than 75% of all observed quality variation in the two panels with a linear regression. Future work and limitations the of the quality model are discussed. ...
Composite lattice structures (CLS) offer high performance and demonstrate significant mass savings in space structure applications. Local modifications of regular lattice designs have the potential to further improve the lattice performance. This research explored the micro-structural quality features of CLSs manufactured with pre-preg fibre-placement, and how quality is impacted by lattice modifications.
Modifications to a regular lattice for a representative case of an attachment point load are identified using a topology optimisation tool. Three lattice modifications techniques were identified: rib width variations, rib angle variations and additional ribs. A sample lattice with modifications was manufactured and evaluated by C-scan, CT techniques and micro-sections. An explanation of quality features in CLS is described and quantified using a presented characterisation model based on node transition waviness.
Using the presented explanation, a quantitative quality model was developed to relate lattice design geometry to manufactured quality for this process. The model was used to design and manufacture a second panel with improved implementation of lattice modifications. The quality model was improved and shown to explain more than 75% of all observed quality variation in the two panels with a linear regression. Future work and limitations the of the quality model are discussed.
Modifications to a regular lattice for a representative case of an attachment point load are identified using a topology optimisation tool. Three lattice modifications techniques were identified: rib width variations, rib angle variations and additional ribs. A sample lattice with modifications was manufactured and evaluated by C-scan, CT techniques and micro-sections. An explanation of quality features in CLS is described and quantified using a presented characterisation model based on node transition waviness.
Using the presented explanation, a quantitative quality model was developed to relate lattice design geometry to manufactured quality for this process. The model was used to design and manufacture a second panel with improved implementation of lattice modifications. The quality model was improved and shown to explain more than 75% of all observed quality variation in the two panels with a linear regression. Future work and limitations the of the quality model are discussed.
An analytical model for stiffness degradation of composite laminates with damage under static or cyclic loading is proposed. For static loading, two different modelling approaches have been created. Both account for shear-induced microscopic matrix damage and matrix cracking within each ply orientation of a laminate. In one approach the residual transverse tensile and shear moduli of a ply are determined by equating the energy density of the undamaged ply to that of the ply with damage, for a same applied load. Predictions excellent agreement with test results for cross-ply laminates, while stiffness degradation is for shear dominated layups. The other static approach applies energy equivalence only to the transverse tensile behavior of a ply. For shear, it predicts the residual shear modulus by accounting for the creation of permanent shear strains. Agreement with test results is excellent for cross-ply laminates, and excellent to good for shear dominated layups. The physical foundation behind this model is not as rigorous as the previous one, and as such needs more work. The proposed fatigue model assumes the matrix strength of a ply to be randomly distributed. Kassapoglou’s residual strength model for fatigue loading is used to express fatigue life as a function of matrix strength. The static model is then used to estimate stiffness degradation as a function the same matrix strength. Connecting the two, stiffness degradation as a function of fatigue cycles is obtained. Validation was performed on cross-ply laminates and agreement with results is excellent.
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An analytical model for stiffness degradation of composite laminates with damage under static or cyclic loading is proposed. For static loading, two different modelling approaches have been created. Both account for shear-induced microscopic matrix damage and matrix cracking within each ply orientation of a laminate. In one approach the residual transverse tensile and shear moduli of a ply are determined by equating the energy density of the undamaged ply to that of the ply with damage, for a same applied load. Predictions excellent agreement with test results for cross-ply laminates, while stiffness degradation is for shear dominated layups. The other static approach applies energy equivalence only to the transverse tensile behavior of a ply. For shear, it predicts the residual shear modulus by accounting for the creation of permanent shear strains. Agreement with test results is excellent for cross-ply laminates, and excellent to good for shear dominated layups. The physical foundation behind this model is not as rigorous as the previous one, and as such needs more work. The proposed fatigue model assumes the matrix strength of a ply to be randomly distributed. Kassapoglou’s residual strength model for fatigue loading is used to express fatigue life as a function of matrix strength. The static model is then used to estimate stiffness degradation as a function the same matrix strength. Connecting the two, stiffness degradation as a function of fatigue cycles is obtained. Validation was performed on cross-ply laminates and agreement with results is excellent.