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O.K. Bergsma
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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.
European hub airports face persistent demand-capacity imbalances generating 22.4 million minutes of delays in 2024, costing €2.8 billion. Traditional reactive approaches prove inefficient for long-haul transatlantic flights. Moreover, long-haul flights have historically been granted exemptions from ground delay programs, meaning short-haul flights disproportionately absorb delays during capacity constraints. This research develops an uncertainty-aware cruise speed control strategy for managing transatlantic arrivals to Amsterdam Schiphol Airport. The methodology decomposes arrival time uncertainty using Johnson distributions conditioned on flight status and temporal horizon, continuously monitoring probability that demand at Initial Approach Fixes exceeds capacity. One-time strategic speed adjustments trigger only when exceedance probability surpasses a predetermined threshold of 70 \%. Fast-time simulation of 30 days using BlueSky and EUROCONTROL trajectory data validates the approach. Across 79 interventions, the strategy achieved 35 \% capacity exceedance certainty reductions on average. These required only 8.72 minutes average delay through conservative Mach reductions of 0.01-0.05. The approach offers a practical, environmentally beneficial pathway for long-range air traffic flow management at capacity-constrained hubs.
...
European hub airports face persistent demand-capacity imbalances generating 22.4 million minutes of delays in 2024, costing €2.8 billion. Traditional reactive approaches prove inefficient for long-haul transatlantic flights. Moreover, long-haul flights have historically been granted exemptions from ground delay programs, meaning short-haul flights disproportionately absorb delays during capacity constraints. This research develops an uncertainty-aware cruise speed control strategy for managing transatlantic arrivals to Amsterdam Schiphol Airport. The methodology decomposes arrival time uncertainty using Johnson distributions conditioned on flight status and temporal horizon, continuously monitoring probability that demand at Initial Approach Fixes exceeds capacity. One-time strategic speed adjustments trigger only when exceedance probability surpasses a predetermined threshold of 70 \%. Fast-time simulation of 30 days using BlueSky and EUROCONTROL trajectory data validates the approach. Across 79 interventions, the strategy achieved 35 \% capacity exceedance certainty reductions on average. These required only 8.72 minutes average delay through conservative Mach reductions of 0.01-0.05. The approach offers a practical, environmentally beneficial pathway for long-range air traffic flow management at capacity-constrained hubs.
Master thesis
(2025)
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Z.A. Ansari, R.C. Alderliesten, Siebe Spronk, Martin Kerschbaum, S. Giovani Pereira Castro, O.K. Bergsma
Composite over-wrapped pressure vessels are the state-of-the-art for hydrogen storage, with Type IV vessels currently using a thermoplastic liner and a thermoset composite. The next innovation, Type V vessels, aims to use a thermoplastic composite over-wrap that acts as both the barrier and container, requiring new materials and manufacturing methods like automated fibre placement.
To accurately characterize the new materials, the effect of their manufacturing process must be captured. While the standard split-disk test exists for wound specimens, it underpredicts their burst strength and fatigue life. Other attempts in literature have improved strength estimations but are not viable in fatigue, thus creating a challenge.
A new test method was developed, which uses a polyurethane ring to apply cyclic internal pressure. It was designed through finite-element analyses, fine-tuned through rigorous tests, and benchmarked against the standard method. It showed improved strain distribution and near-consistent performance in fatigue tests. Hence, it demonstrated potential for more accurate static and fatigue strength characterization of wound composites, with room for improvement through better alignment and even friction. ...
To accurately characterize the new materials, the effect of their manufacturing process must be captured. While the standard split-disk test exists for wound specimens, it underpredicts their burst strength and fatigue life. Other attempts in literature have improved strength estimations but are not viable in fatigue, thus creating a challenge.
A new test method was developed, which uses a polyurethane ring to apply cyclic internal pressure. It was designed through finite-element analyses, fine-tuned through rigorous tests, and benchmarked against the standard method. It showed improved strain distribution and near-consistent performance in fatigue tests. Hence, it demonstrated potential for more accurate static and fatigue strength characterization of wound composites, with room for improvement through better alignment and even friction. ...
Composite over-wrapped pressure vessels are the state-of-the-art for hydrogen storage, with Type IV vessels currently using a thermoplastic liner and a thermoset composite. The next innovation, Type V vessels, aims to use a thermoplastic composite over-wrap that acts as both the barrier and container, requiring new materials and manufacturing methods like automated fibre placement.
To accurately characterize the new materials, the effect of their manufacturing process must be captured. While the standard split-disk test exists for wound specimens, it underpredicts their burst strength and fatigue life. Other attempts in literature have improved strength estimations but are not viable in fatigue, thus creating a challenge.
A new test method was developed, which uses a polyurethane ring to apply cyclic internal pressure. It was designed through finite-element analyses, fine-tuned through rigorous tests, and benchmarked against the standard method. It showed improved strain distribution and near-consistent performance in fatigue tests. Hence, it demonstrated potential for more accurate static and fatigue strength characterization of wound composites, with room for improvement through better alignment and even friction.
To accurately characterize the new materials, the effect of their manufacturing process must be captured. While the standard split-disk test exists for wound specimens, it underpredicts their burst strength and fatigue life. Other attempts in literature have improved strength estimations but are not viable in fatigue, thus creating a challenge.
A new test method was developed, which uses a polyurethane ring to apply cyclic internal pressure. It was designed through finite-element analyses, fine-tuned through rigorous tests, and benchmarked against the standard method. It showed improved strain distribution and near-consistent performance in fatigue tests. Hence, it demonstrated potential for more accurate static and fatigue strength characterization of wound composites, with room for improvement through better alignment and even friction.
This thesis investigates machine learning approaches for predicting the glass transition temperature of polymeric materials using chemical structure representations. Multiple molecular encoding strategies were evaluated, including character‑level tokenization of SMILES strings with count vectorization and TF‑IDF weighting, as well as structural fingerprints such as Morgan and MACCS keys. These representations were applied to a range of models, including Support Vector Regression, Random Forests, Gaussian Process Regression, and deep learning architectures such as Artificial Neural Networks (ANNs) and Convolutional Neural Networks (CNNs). Bayesian optimization via Optuna was employed to tune hyperparameters for optimal performance. Experimental results show that Random Forests combining tokenized SMILES with numerical descriptors achieved competitive predictive accuracy, while fingerprint‑based models provided interpretable and computationally efficient alternatives. The study highlights the trade‑offs between representation richness, interpretability, and prediction, offering insights into the design of data‑driven pipelines for polymer property prediction in aerospace and materials engineering applications.
...
This thesis investigates machine learning approaches for predicting the glass transition temperature of polymeric materials using chemical structure representations. Multiple molecular encoding strategies were evaluated, including character‑level tokenization of SMILES strings with count vectorization and TF‑IDF weighting, as well as structural fingerprints such as Morgan and MACCS keys. These representations were applied to a range of models, including Support Vector Regression, Random Forests, Gaussian Process Regression, and deep learning architectures such as Artificial Neural Networks (ANNs) and Convolutional Neural Networks (CNNs). Bayesian optimization via Optuna was employed to tune hyperparameters for optimal performance. Experimental results show that Random Forests combining tokenized SMILES with numerical descriptors achieved competitive predictive accuracy, while fingerprint‑based models provided interpretable and computationally efficient alternatives. The study highlights the trade‑offs between representation richness, interpretability, and prediction, offering insights into the design of data‑driven pipelines for polymer property prediction in aerospace and materials engineering applications.
Binding Bamboo
The Effect of Chemical Treatments & Manufacturing Process on Bamboo Fibre Reinforced Bio-Based Polycarbonate Composites
This research investigates the feasibility of bamboo fibre-reinforced bio-derived polycarbonate composites for secondary aerospace applications. Motivated by the need for sustainable alternatives to synthetic composites, the study focuses on the effects of chemical fibre treatments on mechanical, thermal, and interfacial performance. Bamboo fibres were treated using alkali (2–8% w/v), silane (2-8g/L), and acetylation methods. Acetylated fibres were excluded early due to structural degradation.
Comprehensive fibre characterisation included density, water absorption, Fourier-transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and single fibre tensile testing. Notably, 2% NaOH-treated fibres exhibited a tensile strength of 249 MPa, and 5 g/L silane-treated fibres reached 194 MPa, compared to 110 MPa for untreated fibres. TGA showed improved thermal stability with onset degradation temperatures of 277◦C for 5 g/L silane compared to 267◦C for untreated fibres.
Treated fibres were used to fabricate unidirectional laminates via solvent-based prepreg processing with Durabio, followed by compression moulding. Composite testing included tensile, flexural, and microscopic cross-sectional analysis. The highest tensile strength of 162 MPa and flexural strength of 184 MPa were recorded for composites with 2 g/L silane-treated fibres, with 5 and 8 g/L silane laminates being only slightly lower than that. Untreated composites recorded 121 MPa and 154 MPa, respectively. Void content decreased from 21% for untreated to 18% for silane-treated, accompanied by a bonding efficiency of 95% for the 5 g/L silane laminate, indicating significantly improved fibre-matrix bonding efficiency. This was supported by optical microscopy, which showed more cohesive interfaces and reduced delamination in silane-treated laminates. Alkali-treated fibres, however, consistently showed worsening properties and quality on the composite level due to fibre degradation and poor bonding.
The study concludes that silane treatment, particularly at 2 g/L, enhances fibre-matrix compatibility, leading to superior composite performance. Future work is recommended in areas including environmental durability, manufacturing optimisation, and closed-loop recycling, with potential expansion to other bio-based matrices. ...
Comprehensive fibre characterisation included density, water absorption, Fourier-transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and single fibre tensile testing. Notably, 2% NaOH-treated fibres exhibited a tensile strength of 249 MPa, and 5 g/L silane-treated fibres reached 194 MPa, compared to 110 MPa for untreated fibres. TGA showed improved thermal stability with onset degradation temperatures of 277◦C for 5 g/L silane compared to 267◦C for untreated fibres.
Treated fibres were used to fabricate unidirectional laminates via solvent-based prepreg processing with Durabio, followed by compression moulding. Composite testing included tensile, flexural, and microscopic cross-sectional analysis. The highest tensile strength of 162 MPa and flexural strength of 184 MPa were recorded for composites with 2 g/L silane-treated fibres, with 5 and 8 g/L silane laminates being only slightly lower than that. Untreated composites recorded 121 MPa and 154 MPa, respectively. Void content decreased from 21% for untreated to 18% for silane-treated, accompanied by a bonding efficiency of 95% for the 5 g/L silane laminate, indicating significantly improved fibre-matrix bonding efficiency. This was supported by optical microscopy, which showed more cohesive interfaces and reduced delamination in silane-treated laminates. Alkali-treated fibres, however, consistently showed worsening properties and quality on the composite level due to fibre degradation and poor bonding.
The study concludes that silane treatment, particularly at 2 g/L, enhances fibre-matrix compatibility, leading to superior composite performance. Future work is recommended in areas including environmental durability, manufacturing optimisation, and closed-loop recycling, with potential expansion to other bio-based matrices. ...
This research investigates the feasibility of bamboo fibre-reinforced bio-derived polycarbonate composites for secondary aerospace applications. Motivated by the need for sustainable alternatives to synthetic composites, the study focuses on the effects of chemical fibre treatments on mechanical, thermal, and interfacial performance. Bamboo fibres were treated using alkali (2–8% w/v), silane (2-8g/L), and acetylation methods. Acetylated fibres were excluded early due to structural degradation.
Comprehensive fibre characterisation included density, water absorption, Fourier-transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and single fibre tensile testing. Notably, 2% NaOH-treated fibres exhibited a tensile strength of 249 MPa, and 5 g/L silane-treated fibres reached 194 MPa, compared to 110 MPa for untreated fibres. TGA showed improved thermal stability with onset degradation temperatures of 277◦C for 5 g/L silane compared to 267◦C for untreated fibres.
Treated fibres were used to fabricate unidirectional laminates via solvent-based prepreg processing with Durabio, followed by compression moulding. Composite testing included tensile, flexural, and microscopic cross-sectional analysis. The highest tensile strength of 162 MPa and flexural strength of 184 MPa were recorded for composites with 2 g/L silane-treated fibres, with 5 and 8 g/L silane laminates being only slightly lower than that. Untreated composites recorded 121 MPa and 154 MPa, respectively. Void content decreased from 21% for untreated to 18% for silane-treated, accompanied by a bonding efficiency of 95% for the 5 g/L silane laminate, indicating significantly improved fibre-matrix bonding efficiency. This was supported by optical microscopy, which showed more cohesive interfaces and reduced delamination in silane-treated laminates. Alkali-treated fibres, however, consistently showed worsening properties and quality on the composite level due to fibre degradation and poor bonding.
The study concludes that silane treatment, particularly at 2 g/L, enhances fibre-matrix compatibility, leading to superior composite performance. Future work is recommended in areas including environmental durability, manufacturing optimisation, and closed-loop recycling, with potential expansion to other bio-based matrices.
Comprehensive fibre characterisation included density, water absorption, Fourier-transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and single fibre tensile testing. Notably, 2% NaOH-treated fibres exhibited a tensile strength of 249 MPa, and 5 g/L silane-treated fibres reached 194 MPa, compared to 110 MPa for untreated fibres. TGA showed improved thermal stability with onset degradation temperatures of 277◦C for 5 g/L silane compared to 267◦C for untreated fibres.
Treated fibres were used to fabricate unidirectional laminates via solvent-based prepreg processing with Durabio, followed by compression moulding. Composite testing included tensile, flexural, and microscopic cross-sectional analysis. The highest tensile strength of 162 MPa and flexural strength of 184 MPa were recorded for composites with 2 g/L silane-treated fibres, with 5 and 8 g/L silane laminates being only slightly lower than that. Untreated composites recorded 121 MPa and 154 MPa, respectively. Void content decreased from 21% for untreated to 18% for silane-treated, accompanied by a bonding efficiency of 95% for the 5 g/L silane laminate, indicating significantly improved fibre-matrix bonding efficiency. This was supported by optical microscopy, which showed more cohesive interfaces and reduced delamination in silane-treated laminates. Alkali-treated fibres, however, consistently showed worsening properties and quality on the composite level due to fibre degradation and poor bonding.
The study concludes that silane treatment, particularly at 2 g/L, enhances fibre-matrix compatibility, leading to superior composite performance. Future work is recommended in areas including environmental durability, manufacturing optimisation, and closed-loop recycling, with potential expansion to other bio-based matrices.
On the Delfi family of satellites, antenna deployment currently takes place using a burn wire system. This requires the antenna to be of the same length as the satellite body. To decouple this length, a new mechanism is needed. Neutrally stable tape springs actuated by shape memory alloys (SMAs) were proposed and studied, a concept previously proposed by Schultz et al in 2008. Thermal analysis, manufacturing tests, and lab testing of SMA actuated tape springs were performed. It was found that the concept can successfully deploy. Satellite integration and more fine-tuning of the mechanism is necessary for an in-flight application.
...
On the Delfi family of satellites, antenna deployment currently takes place using a burn wire system. This requires the antenna to be of the same length as the satellite body. To decouple this length, a new mechanism is needed. Neutrally stable tape springs actuated by shape memory alloys (SMAs) were proposed and studied, a concept previously proposed by Schultz et al in 2008. Thermal analysis, manufacturing tests, and lab testing of SMA actuated tape springs were performed. It was found that the concept can successfully deploy. Satellite integration and more fine-tuning of the mechanism is necessary for an in-flight application.
Modelling of Induction Heating for the Press Consolidation Process
A multi-physics modelling approach to the design of press consolidation tools for thermoplastic composite components
The increasing use of composite materials in aerospace is driven by their high strength-to-weight ratio, but manufacturing these structures represents a large energy footprint and consumption of auxiliary materials. Thermoplastic composites consolidated with Induction heating offers a sustainable alternative to autoclave produced thermosetting composites, eliminating the need for prepreg refrigeration along with most auxiliary materials and a reduction in cycle time and energy consumption. Induction heating, however, is difficult and expensive to test and prototype and therefore there is a need for a way to predict tool behavior.
This thesis develops and builds on a finite element simulation framework in COMSOL Multiphysics to model induction heating of a tool for a C cross-section composite spar, using both, stationary and transient simulations- the latter of which incorporate temperature-dependent material properties - to analyze heating behavior in the tool and the effect of various parameters on the temperature distribution. The simulation model is validated through coil inductance measurements as well as heat surveys on an existing subscale tool.
Design guidelines for tool dimensions, coil placement are derived from simulations and tested virtually on a hypothetical tool geometry. A parametric modeling framework is created in the simulation software package itself, enabling rapid iterations of tool designs, streamlining development. Results demonstrate strong agreement between simulations and experiments with the stationary models predicting the variation in temperatures over the tool better while the transient model calculating the absolute temperatures more accurately. A combination of both these models in conjunction with tool design guidelines presented in this thesis can be potentially used for efficient, first-time-right tooling design for induction heated press consolidation tools.
...
This thesis develops and builds on a finite element simulation framework in COMSOL Multiphysics to model induction heating of a tool for a C cross-section composite spar, using both, stationary and transient simulations- the latter of which incorporate temperature-dependent material properties - to analyze heating behavior in the tool and the effect of various parameters on the temperature distribution. The simulation model is validated through coil inductance measurements as well as heat surveys on an existing subscale tool.
Design guidelines for tool dimensions, coil placement are derived from simulations and tested virtually on a hypothetical tool geometry. A parametric modeling framework is created in the simulation software package itself, enabling rapid iterations of tool designs, streamlining development. Results demonstrate strong agreement between simulations and experiments with the stationary models predicting the variation in temperatures over the tool better while the transient model calculating the absolute temperatures more accurately. A combination of both these models in conjunction with tool design guidelines presented in this thesis can be potentially used for efficient, first-time-right tooling design for induction heated press consolidation tools.
...
The increasing use of composite materials in aerospace is driven by their high strength-to-weight ratio, but manufacturing these structures represents a large energy footprint and consumption of auxiliary materials. Thermoplastic composites consolidated with Induction heating offers a sustainable alternative to autoclave produced thermosetting composites, eliminating the need for prepreg refrigeration along with most auxiliary materials and a reduction in cycle time and energy consumption. Induction heating, however, is difficult and expensive to test and prototype and therefore there is a need for a way to predict tool behavior.
This thesis develops and builds on a finite element simulation framework in COMSOL Multiphysics to model induction heating of a tool for a C cross-section composite spar, using both, stationary and transient simulations- the latter of which incorporate temperature-dependent material properties - to analyze heating behavior in the tool and the effect of various parameters on the temperature distribution. The simulation model is validated through coil inductance measurements as well as heat surveys on an existing subscale tool.
Design guidelines for tool dimensions, coil placement are derived from simulations and tested virtually on a hypothetical tool geometry. A parametric modeling framework is created in the simulation software package itself, enabling rapid iterations of tool designs, streamlining development. Results demonstrate strong agreement between simulations and experiments with the stationary models predicting the variation in temperatures over the tool better while the transient model calculating the absolute temperatures more accurately. A combination of both these models in conjunction with tool design guidelines presented in this thesis can be potentially used for efficient, first-time-right tooling design for induction heated press consolidation tools.
This thesis develops and builds on a finite element simulation framework in COMSOL Multiphysics to model induction heating of a tool for a C cross-section composite spar, using both, stationary and transient simulations- the latter of which incorporate temperature-dependent material properties - to analyze heating behavior in the tool and the effect of various parameters on the temperature distribution. The simulation model is validated through coil inductance measurements as well as heat surveys on an existing subscale tool.
Design guidelines for tool dimensions, coil placement are derived from simulations and tested virtually on a hypothetical tool geometry. A parametric modeling framework is created in the simulation software package itself, enabling rapid iterations of tool designs, streamlining development. Results demonstrate strong agreement between simulations and experiments with the stationary models predicting the variation in temperatures over the tool better while the transient model calculating the absolute temperatures more accurately. A combination of both these models in conjunction with tool design guidelines presented in this thesis can be potentially used for efficient, first-time-right tooling design for induction heated press consolidation tools.
Fatigue Testing of a Deployable Mast
Developing a Methodology for Predicting the Fatigue Life of Deployable Composite Booms
This thesis investigates the low-cycle fatigue behaviour of a deployable composite boom developed in the SpaceMast project at the German Aerospace Center (DLR). The boom, made from a single layer of plain-weave Carbon Fibre Reinforced Polymer (CFRP) with a lenticular cross-section, is intended for small satellite missions requiring compact stowage, low mass, and repeated deployment. However, repeated coiling and uncoiling can induce fatigue damage, motivating a detailed study of the governing mechanisms and life prediction methods.
The research aimed to develop and validate a methodology for assessing fatigue life through combined experimental and analytical approaches. Two key questions were addressed: (1) What mechanisms drive fatigue damage during repeated deployment? and (2) How can fatigue life be predicted for a given boom configuration? Coupon-level bending tests characterised the static and fatigue response of the CFRP material using a custom jig and Digital Image Correlation (DIC). Results revealed non-linear behaviour due to compressive softening and showed that pure bending does not accurately represent operational loading, though it provided insight into stiffness degradation and critical strain limits.
Full-scale deployment tests were then conducted to replicate realistic cycling. Fatigue damage manifested as transverse cracks on the compression side, driven by local buckling and amplified by frictional effects. Excessive coiling tension accelerated failure. The study concludes that fatigue in deployable booms is governed by local buckling and friction, and the developed framework offers a foundation for improving the reliability and design of future space-deployable composite structures. ...
The research aimed to develop and validate a methodology for assessing fatigue life through combined experimental and analytical approaches. Two key questions were addressed: (1) What mechanisms drive fatigue damage during repeated deployment? and (2) How can fatigue life be predicted for a given boom configuration? Coupon-level bending tests characterised the static and fatigue response of the CFRP material using a custom jig and Digital Image Correlation (DIC). Results revealed non-linear behaviour due to compressive softening and showed that pure bending does not accurately represent operational loading, though it provided insight into stiffness degradation and critical strain limits.
Full-scale deployment tests were then conducted to replicate realistic cycling. Fatigue damage manifested as transverse cracks on the compression side, driven by local buckling and amplified by frictional effects. Excessive coiling tension accelerated failure. The study concludes that fatigue in deployable booms is governed by local buckling and friction, and the developed framework offers a foundation for improving the reliability and design of future space-deployable composite structures. ...
This thesis investigates the low-cycle fatigue behaviour of a deployable composite boom developed in the SpaceMast project at the German Aerospace Center (DLR). The boom, made from a single layer of plain-weave Carbon Fibre Reinforced Polymer (CFRP) with a lenticular cross-section, is intended for small satellite missions requiring compact stowage, low mass, and repeated deployment. However, repeated coiling and uncoiling can induce fatigue damage, motivating a detailed study of the governing mechanisms and life prediction methods.
The research aimed to develop and validate a methodology for assessing fatigue life through combined experimental and analytical approaches. Two key questions were addressed: (1) What mechanisms drive fatigue damage during repeated deployment? and (2) How can fatigue life be predicted for a given boom configuration? Coupon-level bending tests characterised the static and fatigue response of the CFRP material using a custom jig and Digital Image Correlation (DIC). Results revealed non-linear behaviour due to compressive softening and showed that pure bending does not accurately represent operational loading, though it provided insight into stiffness degradation and critical strain limits.
Full-scale deployment tests were then conducted to replicate realistic cycling. Fatigue damage manifested as transverse cracks on the compression side, driven by local buckling and amplified by frictional effects. Excessive coiling tension accelerated failure. The study concludes that fatigue in deployable booms is governed by local buckling and friction, and the developed framework offers a foundation for improving the reliability and design of future space-deployable composite structures.
The research aimed to develop and validate a methodology for assessing fatigue life through combined experimental and analytical approaches. Two key questions were addressed: (1) What mechanisms drive fatigue damage during repeated deployment? and (2) How can fatigue life be predicted for a given boom configuration? Coupon-level bending tests characterised the static and fatigue response of the CFRP material using a custom jig and Digital Image Correlation (DIC). Results revealed non-linear behaviour due to compressive softening and showed that pure bending does not accurately represent operational loading, though it provided insight into stiffness degradation and critical strain limits.
Full-scale deployment tests were then conducted to replicate realistic cycling. Fatigue damage manifested as transverse cracks on the compression side, driven by local buckling and amplified by frictional effects. Excessive coiling tension accelerated failure. The study concludes that fatigue in deployable booms is governed by local buckling and friction, and the developed framework offers a foundation for improving the reliability and design of future space-deployable composite structures.
Master thesis
(2025)
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T. Iyer, O.K. Bergsma, N. Eleftheroglou, S. Giovani Pereira Castro, H.F. Maathuis
Inverse design is a concept where one can design a structure via a property-first approach, where the properties of a system act as precursor information to guide the search for a viable design. This concept is classified as one of two: indirect or direct. While the former is no different than a forward-based approach using traditional optimization, a direct inverse design framework attempts to invert the process and directly map the desired properties to a suitable design candidate, which is unconventional. As such, the design process can be positively radicalized, with regards to the required computational resources when designing multiple structures.
In this work, the use of Bayesian machine learning, more specifically Bayesian optimization using Gaussian process regression, is employed to construct a direct inverse design framework using the design of mass-optimized fixed-wing aircraft ribs against buckling as the validation case study in 1, 6, and 10 dimensions. The results are compared to an indirect approach using the same algorithms and demonstrate that barring certain limitations, which are not inherent flaws of the direct approach, the framework designed not only demonstrates sound potential in inverting the forward map, but outperforms the indirect approach when designing multiple structures.
This research equally provides a stepping stone towards future research possibilities in the same field, all culminating in the improvement of the multi-disciplinary design process.
...
In this work, the use of Bayesian machine learning, more specifically Bayesian optimization using Gaussian process regression, is employed to construct a direct inverse design framework using the design of mass-optimized fixed-wing aircraft ribs against buckling as the validation case study in 1, 6, and 10 dimensions. The results are compared to an indirect approach using the same algorithms and demonstrate that barring certain limitations, which are not inherent flaws of the direct approach, the framework designed not only demonstrates sound potential in inverting the forward map, but outperforms the indirect approach when designing multiple structures.
This research equally provides a stepping stone towards future research possibilities in the same field, all culminating in the improvement of the multi-disciplinary design process.
...
Inverse design is a concept where one can design a structure via a property-first approach, where the properties of a system act as precursor information to guide the search for a viable design. This concept is classified as one of two: indirect or direct. While the former is no different than a forward-based approach using traditional optimization, a direct inverse design framework attempts to invert the process and directly map the desired properties to a suitable design candidate, which is unconventional. As such, the design process can be positively radicalized, with regards to the required computational resources when designing multiple structures.
In this work, the use of Bayesian machine learning, more specifically Bayesian optimization using Gaussian process regression, is employed to construct a direct inverse design framework using the design of mass-optimized fixed-wing aircraft ribs against buckling as the validation case study in 1, 6, and 10 dimensions. The results are compared to an indirect approach using the same algorithms and demonstrate that barring certain limitations, which are not inherent flaws of the direct approach, the framework designed not only demonstrates sound potential in inverting the forward map, but outperforms the indirect approach when designing multiple structures.
This research equally provides a stepping stone towards future research possibilities in the same field, all culminating in the improvement of the multi-disciplinary design process.
In this work, the use of Bayesian machine learning, more specifically Bayesian optimization using Gaussian process regression, is employed to construct a direct inverse design framework using the design of mass-optimized fixed-wing aircraft ribs against buckling as the validation case study in 1, 6, and 10 dimensions. The results are compared to an indirect approach using the same algorithms and demonstrate that barring certain limitations, which are not inherent flaws of the direct approach, the framework designed not only demonstrates sound potential in inverting the forward map, but outperforms the indirect approach when designing multiple structures.
This research equally provides a stepping stone towards future research possibilities in the same field, all culminating in the improvement of the multi-disciplinary design process.
The environmental impact of composite materials is a growing concern across numerous industries, prompting the need for sustainable alternatives. Bamboo fibre reinforced polymers (BFRPs) have emerged as a promising solution thanks to their high CO_2 capture leading to lower environmental footprint. A novel extraction method, developed and patented by Bambooder, aims to extract bamboo fibres through a purely mechanical industrial process while preserving their maximum performance. These fibres currently in development, necessitate comprehensive material characterisation.
In this study, BFRPs were produced using fibres provided by Bambooder, combined with polypropylene (PP) and polyamide 11 (PA11) through compression moulding, and with epoxy using resin-infusion composite production methods. The density of fibres was measured at 1.16 g/cm^3. The highest composite performance was achieved with epoxy, revealing a tensile back-calculated fibre modulus of 54.2 GPa and a strength of 509.6 MPa. These properties are higher than properties observed in current literature, having a tensile modulus and strength of approximately 36 GPa and 503 MPa respectively. Similarly, flexural back-calculated fibre properties showed a modulus of 44.6 GPa and a strength of 484.7 MPa.
Thermoplastic laminate testing demonstrated good bonding performance with PA11, attributed to the formation of hydrogen bonds at the fibre-matrix interface due to the polymer's non-polarity. In contrast, PP exhibited poor interfacial bonding. Additional fibre combing improved mechanical performance by up to 20% in tensile modulus and 9% in tensile strength, attributed to better fibre quality, improved fibre orientation, and increased fibre dispersion.
This thesis therefore validates the use of bamboo fibres for structural composite applications and highlights their potential as sustainable engineering materials, promoting the adoption of natural fibre composites such as BFRPs in various industrial sectors. ...
The environmental impact of composite materials is a growing concern across numerous industries, prompting the need for sustainable alternatives. Bamboo fibre reinforced polymers (BFRPs) have emerged as a promising solution thanks to their high CO_2 capture leading to lower environmental footprint. A novel extraction method, developed and patented by Bambooder, aims to extract bamboo fibres through a purely mechanical industrial process while preserving their maximum performance. These fibres currently in development, necessitate comprehensive material characterisation.
In this study, BFRPs were produced using fibres provided by Bambooder, combined with polypropylene (PP) and polyamide 11 (PA11) through compression moulding, and with epoxy using resin-infusion composite production methods. The density of fibres was measured at 1.16 g/cm^3. The highest composite performance was achieved with epoxy, revealing a tensile back-calculated fibre modulus of 54.2 GPa and a strength of 509.6 MPa. These properties are higher than properties observed in current literature, having a tensile modulus and strength of approximately 36 GPa and 503 MPa respectively. Similarly, flexural back-calculated fibre properties showed a modulus of 44.6 GPa and a strength of 484.7 MPa.
Thermoplastic laminate testing demonstrated good bonding performance with PA11, attributed to the formation of hydrogen bonds at the fibre-matrix interface due to the polymer's non-polarity. In contrast, PP exhibited poor interfacial bonding. Additional fibre combing improved mechanical performance by up to 20% in tensile modulus and 9% in tensile strength, attributed to better fibre quality, improved fibre orientation, and increased fibre dispersion.
This thesis therefore validates the use of bamboo fibres for structural composite applications and highlights their potential as sustainable engineering materials, promoting the adoption of natural fibre composites such as BFRPs in various industrial sectors.
Master thesis
(2024)
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R. Connolly, S.J. Garcia Espallargas, M.J. Tavaststjerna, J.A. Pascoe, O.K. Bergsma
Ice accumulation on aircraft surfaces is a prevalent issue, and icephobic coating strategies can be implemented to assist in the removal of or ice on an aircraft. However little is known regarding the effects of novel icephobic coatings and surfaces on ice adhesion strength, which is difficult to measure and quantify, and is typically reported in literature with a high standard deviation and scatter. In this thesis, a reliable set-up for testing ice adhesion strength is successfully designed, constructed, and validated. Using this set-up, it is possible to examine the relationships between various surface parameters and ice adhesion strength, and to analyse the scatter in order correlate the results both qualitatively and quantitatively. Additionally, the influence of material and topology on the adhesion strength and failure mechanisms of ice is investigated.
...
Ice accumulation on aircraft surfaces is a prevalent issue, and icephobic coating strategies can be implemented to assist in the removal of or ice on an aircraft. However little is known regarding the effects of novel icephobic coatings and surfaces on ice adhesion strength, which is difficult to measure and quantify, and is typically reported in literature with a high standard deviation and scatter. In this thesis, a reliable set-up for testing ice adhesion strength is successfully designed, constructed, and validated. Using this set-up, it is possible to examine the relationships between various surface parameters and ice adhesion strength, and to analyse the scatter in order correlate the results both qualitatively and quantitatively. Additionally, the influence of material and topology on the adhesion strength and failure mechanisms of ice is investigated.
3D Printing Bioinspired, Bacteria-Embedded Ceramic Composites
Towards manufacturing shaped, strong, tough, and eco-friendly materials
Our reliance on synthetic structural materials has contributed extensively to environmental degradation, resource depletion, and pollution. The urgent need for sustainable alternatives has sparked interest in bio-based materials that align with Nature's cycles while maintaining high performance. However, finding such alternatives has remained challenging, especially for ceramics, which typically require high-temperature processes to achieve structural integrity. Yet Nature offers a promising blueprint: the nacreous layer, "mother of pearl", found in molluscan shells. Millions of years have allowed these invertebrates to evolve remarkable defect tolerance, achieving strength, stiffness, and toughness - a combination elusive in most conventional ceramics.
Despite extensive efforts, mimicking the intricate microstructure of nacre to achieve new, advanced materials remains challenging. Recent studies have leveraged the outstanding shaping freedom and microstructural control offered by additive manufacturing to provide new opportunities. However, these approaches continue to rely on sintering to improve mechanical properties, thereby undermining their ecological potential. The underlying printing process also remains largely unexplored. This thesis confronts both challenges by exploring a novel bacterial stiffening approach in direct ink writing using various material compositions. For the first time, mineral-depositing bacteria are incorporated into a ceramic-biopolymer suspension in an attempt to achieve sinter-like stiffening of the structure at reduced energy expenditure.
Direct ink writing ceramic-polymer bioinks is challenging due to the sensitivity of colloidal dispersions to changes in electrostatic and steric interactions, further complicated by strongly time-dependent rheology. These aspects hindered exploring the effects of biomineralisation on material performance. A 'printing window' is identified, beyond which bacteria-induced coagulation disrupts extrusion, establishing an essential constraint. Printability may be improved by controlling pH, performing more appropriate rheological experiments, and tuning rheology. Nutrient and bacterial content reduced material strength, meaning that any positive effect of biomineralisation must at least overcome this negative influence to provide a net benefit. Excessively high void content highlights the need to maximise compaction and solid content. Crucially, biomineralisation was achieved in preliminary tests, suggesting that the approach is fundamentally promising. These findings provide critical insights and guidelines for developing shaped, strong, tough, and sustainable ceramic materials, paving the way towards eco-friendly materials inspired and built by Nature. ...
Despite extensive efforts, mimicking the intricate microstructure of nacre to achieve new, advanced materials remains challenging. Recent studies have leveraged the outstanding shaping freedom and microstructural control offered by additive manufacturing to provide new opportunities. However, these approaches continue to rely on sintering to improve mechanical properties, thereby undermining their ecological potential. The underlying printing process also remains largely unexplored. This thesis confronts both challenges by exploring a novel bacterial stiffening approach in direct ink writing using various material compositions. For the first time, mineral-depositing bacteria are incorporated into a ceramic-biopolymer suspension in an attempt to achieve sinter-like stiffening of the structure at reduced energy expenditure.
Direct ink writing ceramic-polymer bioinks is challenging due to the sensitivity of colloidal dispersions to changes in electrostatic and steric interactions, further complicated by strongly time-dependent rheology. These aspects hindered exploring the effects of biomineralisation on material performance. A 'printing window' is identified, beyond which bacteria-induced coagulation disrupts extrusion, establishing an essential constraint. Printability may be improved by controlling pH, performing more appropriate rheological experiments, and tuning rheology. Nutrient and bacterial content reduced material strength, meaning that any positive effect of biomineralisation must at least overcome this negative influence to provide a net benefit. Excessively high void content highlights the need to maximise compaction and solid content. Crucially, biomineralisation was achieved in preliminary tests, suggesting that the approach is fundamentally promising. These findings provide critical insights and guidelines for developing shaped, strong, tough, and sustainable ceramic materials, paving the way towards eco-friendly materials inspired and built by Nature. ...
Our reliance on synthetic structural materials has contributed extensively to environmental degradation, resource depletion, and pollution. The urgent need for sustainable alternatives has sparked interest in bio-based materials that align with Nature's cycles while maintaining high performance. However, finding such alternatives has remained challenging, especially for ceramics, which typically require high-temperature processes to achieve structural integrity. Yet Nature offers a promising blueprint: the nacreous layer, "mother of pearl", found in molluscan shells. Millions of years have allowed these invertebrates to evolve remarkable defect tolerance, achieving strength, stiffness, and toughness - a combination elusive in most conventional ceramics.
Despite extensive efforts, mimicking the intricate microstructure of nacre to achieve new, advanced materials remains challenging. Recent studies have leveraged the outstanding shaping freedom and microstructural control offered by additive manufacturing to provide new opportunities. However, these approaches continue to rely on sintering to improve mechanical properties, thereby undermining their ecological potential. The underlying printing process also remains largely unexplored. This thesis confronts both challenges by exploring a novel bacterial stiffening approach in direct ink writing using various material compositions. For the first time, mineral-depositing bacteria are incorporated into a ceramic-biopolymer suspension in an attempt to achieve sinter-like stiffening of the structure at reduced energy expenditure.
Direct ink writing ceramic-polymer bioinks is challenging due to the sensitivity of colloidal dispersions to changes in electrostatic and steric interactions, further complicated by strongly time-dependent rheology. These aspects hindered exploring the effects of biomineralisation on material performance. A 'printing window' is identified, beyond which bacteria-induced coagulation disrupts extrusion, establishing an essential constraint. Printability may be improved by controlling pH, performing more appropriate rheological experiments, and tuning rheology. Nutrient and bacterial content reduced material strength, meaning that any positive effect of biomineralisation must at least overcome this negative influence to provide a net benefit. Excessively high void content highlights the need to maximise compaction and solid content. Crucially, biomineralisation was achieved in preliminary tests, suggesting that the approach is fundamentally promising. These findings provide critical insights and guidelines for developing shaped, strong, tough, and sustainable ceramic materials, paving the way towards eco-friendly materials inspired and built by Nature.
Despite extensive efforts, mimicking the intricate microstructure of nacre to achieve new, advanced materials remains challenging. Recent studies have leveraged the outstanding shaping freedom and microstructural control offered by additive manufacturing to provide new opportunities. However, these approaches continue to rely on sintering to improve mechanical properties, thereby undermining their ecological potential. The underlying printing process also remains largely unexplored. This thesis confronts both challenges by exploring a novel bacterial stiffening approach in direct ink writing using various material compositions. For the first time, mineral-depositing bacteria are incorporated into a ceramic-biopolymer suspension in an attempt to achieve sinter-like stiffening of the structure at reduced energy expenditure.
Direct ink writing ceramic-polymer bioinks is challenging due to the sensitivity of colloidal dispersions to changes in electrostatic and steric interactions, further complicated by strongly time-dependent rheology. These aspects hindered exploring the effects of biomineralisation on material performance. A 'printing window' is identified, beyond which bacteria-induced coagulation disrupts extrusion, establishing an essential constraint. Printability may be improved by controlling pH, performing more appropriate rheological experiments, and tuning rheology. Nutrient and bacterial content reduced material strength, meaning that any positive effect of biomineralisation must at least overcome this negative influence to provide a net benefit. Excessively high void content highlights the need to maximise compaction and solid content. Crucially, biomineralisation was achieved in preliminary tests, suggesting that the approach is fundamentally promising. These findings provide critical insights and guidelines for developing shaped, strong, tough, and sustainable ceramic materials, paving the way towards eco-friendly materials inspired and built by Nature.
Stiff and transparent materials are essential across industries such as aerospace, defense, and consumer electronics. Traditional materials like glass and ceramics, while effective, have limitations due to brittleness, high density, and low impact resistance. Consequently, there is a demand for lightweight, durable materials with favorable optical properties. Fiber-reinforced polymers (FRPs) offer high strength-to-weight ratios and greater impact resistance than glass and ceramics. Given the low light absorption of glass fibers in the visible spectrum, transparent glass fiber-reinforced polymers (TGFRPs) show promise as replacements for traditional transparent materials.
This thesis explores two main aspects: (1) optimizing TGFRP transparency through manufacturing parameters and (2) leveraging TGFRP transparency for damage detection and stress analysis. In the first phase, findings demonstrate that achieving high surface smoothness and maximizing light transmission within the green spectrum (520–600 nm) are crucial for enhancing TGFRP transparency. This is best controlled via post-curing, a more stable approach than adding methyl methacrylate (MMA) as suggested in existing literature. Sizing was also found to play a critical role in transparency, ensuring optimal bonding between glass fibers and the matrix. Additionally, minimizing the number of glass fiber fabric layers improved transparency by reducing transmission losses across visible wavelengths.
The second phase investigated the transparency of TGFRP for visualizing internal damage and stress distributions. Confocal microscopy was used to observe cracks at various depths within TGFRP samples, while image processing techniques, such as thresholding, were employed to calculate crack density. The results indicate that a higher crack density corresponds to reduced light transmittance across the visible range. However, some limitations were encountered, as cracks and scratches on the upper layers cast shadows on the lower layers, complicating the detection of deeper damage.
During tensile testing of open-hole specimens, significant opacity changes were observed in high-strain regions, suggesting that opacity correlates with localized stress. Digital image correlation (DIC) and grayscale histogram analysis provided insights into the strain thresholds at which opacity changes begin. Future work could build on this by examining the extent to which opacity changes are due to refractive index variations alone, independent of crack formation, using these strain levels as a baseline.
Furthermore, verifying the reversibility of opacity changes through post-test spectrophotometry could position TGFRPs as highly effective materials for developing innovative and reliable non-destructive testing, damage detection, and stress visualization methods in glass fiber-reinforced polymer composites.
...
This thesis explores two main aspects: (1) optimizing TGFRP transparency through manufacturing parameters and (2) leveraging TGFRP transparency for damage detection and stress analysis. In the first phase, findings demonstrate that achieving high surface smoothness and maximizing light transmission within the green spectrum (520–600 nm) are crucial for enhancing TGFRP transparency. This is best controlled via post-curing, a more stable approach than adding methyl methacrylate (MMA) as suggested in existing literature. Sizing was also found to play a critical role in transparency, ensuring optimal bonding between glass fibers and the matrix. Additionally, minimizing the number of glass fiber fabric layers improved transparency by reducing transmission losses across visible wavelengths.
The second phase investigated the transparency of TGFRP for visualizing internal damage and stress distributions. Confocal microscopy was used to observe cracks at various depths within TGFRP samples, while image processing techniques, such as thresholding, were employed to calculate crack density. The results indicate that a higher crack density corresponds to reduced light transmittance across the visible range. However, some limitations were encountered, as cracks and scratches on the upper layers cast shadows on the lower layers, complicating the detection of deeper damage.
During tensile testing of open-hole specimens, significant opacity changes were observed in high-strain regions, suggesting that opacity correlates with localized stress. Digital image correlation (DIC) and grayscale histogram analysis provided insights into the strain thresholds at which opacity changes begin. Future work could build on this by examining the extent to which opacity changes are due to refractive index variations alone, independent of crack formation, using these strain levels as a baseline.
Furthermore, verifying the reversibility of opacity changes through post-test spectrophotometry could position TGFRPs as highly effective materials for developing innovative and reliable non-destructive testing, damage detection, and stress visualization methods in glass fiber-reinforced polymer composites.
...
Stiff and transparent materials are essential across industries such as aerospace, defense, and consumer electronics. Traditional materials like glass and ceramics, while effective, have limitations due to brittleness, high density, and low impact resistance. Consequently, there is a demand for lightweight, durable materials with favorable optical properties. Fiber-reinforced polymers (FRPs) offer high strength-to-weight ratios and greater impact resistance than glass and ceramics. Given the low light absorption of glass fibers in the visible spectrum, transparent glass fiber-reinforced polymers (TGFRPs) show promise as replacements for traditional transparent materials.
This thesis explores two main aspects: (1) optimizing TGFRP transparency through manufacturing parameters and (2) leveraging TGFRP transparency for damage detection and stress analysis. In the first phase, findings demonstrate that achieving high surface smoothness and maximizing light transmission within the green spectrum (520–600 nm) are crucial for enhancing TGFRP transparency. This is best controlled via post-curing, a more stable approach than adding methyl methacrylate (MMA) as suggested in existing literature. Sizing was also found to play a critical role in transparency, ensuring optimal bonding between glass fibers and the matrix. Additionally, minimizing the number of glass fiber fabric layers improved transparency by reducing transmission losses across visible wavelengths.
The second phase investigated the transparency of TGFRP for visualizing internal damage and stress distributions. Confocal microscopy was used to observe cracks at various depths within TGFRP samples, while image processing techniques, such as thresholding, were employed to calculate crack density. The results indicate that a higher crack density corresponds to reduced light transmittance across the visible range. However, some limitations were encountered, as cracks and scratches on the upper layers cast shadows on the lower layers, complicating the detection of deeper damage.
During tensile testing of open-hole specimens, significant opacity changes were observed in high-strain regions, suggesting that opacity correlates with localized stress. Digital image correlation (DIC) and grayscale histogram analysis provided insights into the strain thresholds at which opacity changes begin. Future work could build on this by examining the extent to which opacity changes are due to refractive index variations alone, independent of crack formation, using these strain levels as a baseline.
Furthermore, verifying the reversibility of opacity changes through post-test spectrophotometry could position TGFRPs as highly effective materials for developing innovative and reliable non-destructive testing, damage detection, and stress visualization methods in glass fiber-reinforced polymer composites.
This thesis explores two main aspects: (1) optimizing TGFRP transparency through manufacturing parameters and (2) leveraging TGFRP transparency for damage detection and stress analysis. In the first phase, findings demonstrate that achieving high surface smoothness and maximizing light transmission within the green spectrum (520–600 nm) are crucial for enhancing TGFRP transparency. This is best controlled via post-curing, a more stable approach than adding methyl methacrylate (MMA) as suggested in existing literature. Sizing was also found to play a critical role in transparency, ensuring optimal bonding between glass fibers and the matrix. Additionally, minimizing the number of glass fiber fabric layers improved transparency by reducing transmission losses across visible wavelengths.
The second phase investigated the transparency of TGFRP for visualizing internal damage and stress distributions. Confocal microscopy was used to observe cracks at various depths within TGFRP samples, while image processing techniques, such as thresholding, were employed to calculate crack density. The results indicate that a higher crack density corresponds to reduced light transmittance across the visible range. However, some limitations were encountered, as cracks and scratches on the upper layers cast shadows on the lower layers, complicating the detection of deeper damage.
During tensile testing of open-hole specimens, significant opacity changes were observed in high-strain regions, suggesting that opacity correlates with localized stress. Digital image correlation (DIC) and grayscale histogram analysis provided insights into the strain thresholds at which opacity changes begin. Future work could build on this by examining the extent to which opacity changes are due to refractive index variations alone, independent of crack formation, using these strain levels as a baseline.
Furthermore, verifying the reversibility of opacity changes through post-test spectrophotometry could position TGFRPs as highly effective materials for developing innovative and reliable non-destructive testing, damage detection, and stress visualization methods in glass fiber-reinforced polymer composites.
In this thesis project, the out-of-autoclave process for the manufacturing of a thermoplastic wing rib was analyzed, with the goal of improving the robustness of the manufacturing process. The C/PEKK wing rib was manufactured by assembling the constituent laminates in an out-of-autoclave tool subjected to two-side heating.
The quality of the manufactured rib was evaluated using dimensional and non-destructive inspection (NDI) criteria to assess the consistency and robustness of the manufacturing process. Thermal behavior of the consolidation tool was analyzed to identify any temperature outliers that could negatively impact the rib quality. Additionally, the movement of the tool block in contact with the rib foot was monitored to determine if there was any correlation between the tool block movement and the quality of the rib foot.
For the T-joint configuration on the rib, two types of fillers were tested under tension loading: a lay-up filler and a 3D printed filler. The large radius of the web flanges in the rib made the filler a non-inspectable region in the rib, which could not be evaluated for defects using conventional NDI techniques. Therefore, the role of defects around the filler in the wing rib was examined by simulating defects in the filler/flange radius junction. Mechanical testing under tension loading was performed on samples made from the manufactured ribs to assess the severity of performance reduction due to simulated defects.
The research concluded that temperature distribution in the tool and part was not responsible for non-compliant parts; however, the pressure application required optimization. No significant correlation between the movement of the foot tool block and the achieved part quality was identified. The presence of defects around the filler resulted in a reduction in performance under tension loading, highlighting the importance of minimizing defects at the radius/filler interface.
...
The quality of the manufactured rib was evaluated using dimensional and non-destructive inspection (NDI) criteria to assess the consistency and robustness of the manufacturing process. Thermal behavior of the consolidation tool was analyzed to identify any temperature outliers that could negatively impact the rib quality. Additionally, the movement of the tool block in contact with the rib foot was monitored to determine if there was any correlation between the tool block movement and the quality of the rib foot.
For the T-joint configuration on the rib, two types of fillers were tested under tension loading: a lay-up filler and a 3D printed filler. The large radius of the web flanges in the rib made the filler a non-inspectable region in the rib, which could not be evaluated for defects using conventional NDI techniques. Therefore, the role of defects around the filler in the wing rib was examined by simulating defects in the filler/flange radius junction. Mechanical testing under tension loading was performed on samples made from the manufactured ribs to assess the severity of performance reduction due to simulated defects.
The research concluded that temperature distribution in the tool and part was not responsible for non-compliant parts; however, the pressure application required optimization. No significant correlation between the movement of the foot tool block and the achieved part quality was identified. The presence of defects around the filler resulted in a reduction in performance under tension loading, highlighting the importance of minimizing defects at the radius/filler interface.
...
In this thesis project, the out-of-autoclave process for the manufacturing of a thermoplastic wing rib was analyzed, with the goal of improving the robustness of the manufacturing process. The C/PEKK wing rib was manufactured by assembling the constituent laminates in an out-of-autoclave tool subjected to two-side heating.
The quality of the manufactured rib was evaluated using dimensional and non-destructive inspection (NDI) criteria to assess the consistency and robustness of the manufacturing process. Thermal behavior of the consolidation tool was analyzed to identify any temperature outliers that could negatively impact the rib quality. Additionally, the movement of the tool block in contact with the rib foot was monitored to determine if there was any correlation between the tool block movement and the quality of the rib foot.
For the T-joint configuration on the rib, two types of fillers were tested under tension loading: a lay-up filler and a 3D printed filler. The large radius of the web flanges in the rib made the filler a non-inspectable region in the rib, which could not be evaluated for defects using conventional NDI techniques. Therefore, the role of defects around the filler in the wing rib was examined by simulating defects in the filler/flange radius junction. Mechanical testing under tension loading was performed on samples made from the manufactured ribs to assess the severity of performance reduction due to simulated defects.
The research concluded that temperature distribution in the tool and part was not responsible for non-compliant parts; however, the pressure application required optimization. No significant correlation between the movement of the foot tool block and the achieved part quality was identified. The presence of defects around the filler resulted in a reduction in performance under tension loading, highlighting the importance of minimizing defects at the radius/filler interface.
The quality of the manufactured rib was evaluated using dimensional and non-destructive inspection (NDI) criteria to assess the consistency and robustness of the manufacturing process. Thermal behavior of the consolidation tool was analyzed to identify any temperature outliers that could negatively impact the rib quality. Additionally, the movement of the tool block in contact with the rib foot was monitored to determine if there was any correlation between the tool block movement and the quality of the rib foot.
For the T-joint configuration on the rib, two types of fillers were tested under tension loading: a lay-up filler and a 3D printed filler. The large radius of the web flanges in the rib made the filler a non-inspectable region in the rib, which could not be evaluated for defects using conventional NDI techniques. Therefore, the role of defects around the filler in the wing rib was examined by simulating defects in the filler/flange radius junction. Mechanical testing under tension loading was performed on samples made from the manufactured ribs to assess the severity of performance reduction due to simulated defects.
The research concluded that temperature distribution in the tool and part was not responsible for non-compliant parts; however, the pressure application required optimization. No significant correlation between the movement of the foot tool block and the achieved part quality was identified. The presence of defects around the filler resulted in a reduction in performance under tension loading, highlighting the importance of minimizing defects at the radius/filler interface.
Listening to liquid hydrogen tanks
A feasibility study into localising damage in double-walled tanks using acoustic emssion
To facilitate the transition to liquid hydrogen (LH2) as an alternative aircraft fuel, the stor age tanks need to be closely monitored to allow for safe operation. This research explores the feasibility of using an acoustic emission-based structural health monitoring method to detect and localise simulated damage on a metal double-walled vacuum insulated tank. The complicated inner and outer tank geometry makes it a novel application of an established method.
To be able to perform experiments, a metal double-walled vacuum insulated tank with a fixed and flexible support was cut in half to make the inner tank accessible. Pencil lead break tests were performed on the inner and outer tank and recorded by lead zirconate titanate (PZT) sensors to assess localisation accuracy. It was found that a pencil lead break (PLB) performed on the inner tank could be detected by a sensor placed on the outer tank. Subsequently, an accuracy of 80% was achieved in making the distinction whether the PLB was located on the inner or outer tank. For the PLBs placed on the inner tank a 1D localisation accuracy of 17 [mm] and 21 [mm] was achievable for the flexible and fixed support respectively. For the outer tank a 1D localisation accuracy of 46 [mm] was achievable, while for 2D localisation this was 41 [mm].
It is concluded that with sensors placed solely on the outer tank, both the inner and outer tank can be monitored. Additionally, simulated damage on the inner and outer tank could be localised with an accuracy below 10% of the tank’s dimension. Therefore, based on the feasibility study performed, acoustic emission-based structural health monitoring is deemed a viable method to enhance the reliability and safety of metal double-walled vacuum insulated LH2 tanks. ...
To be able to perform experiments, a metal double-walled vacuum insulated tank with a fixed and flexible support was cut in half to make the inner tank accessible. Pencil lead break tests were performed on the inner and outer tank and recorded by lead zirconate titanate (PZT) sensors to assess localisation accuracy. It was found that a pencil lead break (PLB) performed on the inner tank could be detected by a sensor placed on the outer tank. Subsequently, an accuracy of 80% was achieved in making the distinction whether the PLB was located on the inner or outer tank. For the PLBs placed on the inner tank a 1D localisation accuracy of 17 [mm] and 21 [mm] was achievable for the flexible and fixed support respectively. For the outer tank a 1D localisation accuracy of 46 [mm] was achievable, while for 2D localisation this was 41 [mm].
It is concluded that with sensors placed solely on the outer tank, both the inner and outer tank can be monitored. Additionally, simulated damage on the inner and outer tank could be localised with an accuracy below 10% of the tank’s dimension. Therefore, based on the feasibility study performed, acoustic emission-based structural health monitoring is deemed a viable method to enhance the reliability and safety of metal double-walled vacuum insulated LH2 tanks. ...
To facilitate the transition to liquid hydrogen (LH2) as an alternative aircraft fuel, the stor age tanks need to be closely monitored to allow for safe operation. This research explores the feasibility of using an acoustic emission-based structural health monitoring method to detect and localise simulated damage on a metal double-walled vacuum insulated tank. The complicated inner and outer tank geometry makes it a novel application of an established method.
To be able to perform experiments, a metal double-walled vacuum insulated tank with a fixed and flexible support was cut in half to make the inner tank accessible. Pencil lead break tests were performed on the inner and outer tank and recorded by lead zirconate titanate (PZT) sensors to assess localisation accuracy. It was found that a pencil lead break (PLB) performed on the inner tank could be detected by a sensor placed on the outer tank. Subsequently, an accuracy of 80% was achieved in making the distinction whether the PLB was located on the inner or outer tank. For the PLBs placed on the inner tank a 1D localisation accuracy of 17 [mm] and 21 [mm] was achievable for the flexible and fixed support respectively. For the outer tank a 1D localisation accuracy of 46 [mm] was achievable, while for 2D localisation this was 41 [mm].
It is concluded that with sensors placed solely on the outer tank, both the inner and outer tank can be monitored. Additionally, simulated damage on the inner and outer tank could be localised with an accuracy below 10% of the tank’s dimension. Therefore, based on the feasibility study performed, acoustic emission-based structural health monitoring is deemed a viable method to enhance the reliability and safety of metal double-walled vacuum insulated LH2 tanks.
To be able to perform experiments, a metal double-walled vacuum insulated tank with a fixed and flexible support was cut in half to make the inner tank accessible. Pencil lead break tests were performed on the inner and outer tank and recorded by lead zirconate titanate (PZT) sensors to assess localisation accuracy. It was found that a pencil lead break (PLB) performed on the inner tank could be detected by a sensor placed on the outer tank. Subsequently, an accuracy of 80% was achieved in making the distinction whether the PLB was located on the inner or outer tank. For the PLBs placed on the inner tank a 1D localisation accuracy of 17 [mm] and 21 [mm] was achievable for the flexible and fixed support respectively. For the outer tank a 1D localisation accuracy of 46 [mm] was achievable, while for 2D localisation this was 41 [mm].
It is concluded that with sensors placed solely on the outer tank, both the inner and outer tank can be monitored. Additionally, simulated damage on the inner and outer tank could be localised with an accuracy below 10% of the tank’s dimension. Therefore, based on the feasibility study performed, acoustic emission-based structural health monitoring is deemed a viable method to enhance the reliability and safety of metal double-walled vacuum insulated LH2 tanks.
The aerospace sector continues to drive innovations in high-performance materials. These materials however, tend to have energy intensive and emission heavy manufacturing processes. One of the most commonly used materials in aircrafts today are polymer matrix composites consisting of reinforcement fibers and a matrix. While the fibers provide the most strength to the composite, the matrix holds the fibers together and transfers the loads to them. The most commonly used matrix material today is made of BADGE (Bisphenol A Diglycidyl Ether), a material which is toxic to humans and comes from fossil-based products.
This thesis investigates the viability of a vanillin-derived bio-based alternative, VDE (Vanillyl Alcohol Diglycidyl Ether), to be used in high-performance composites for aerospace applications. VDE monomer is derived from vanillin, which is obtained from lignin, a material present in 35% of woody plants. The VDE-DDS resin system, when cured, exhibited comparable thermal and physical properties, such as glass transition temperature and heat deflection temperature, to traditional aerospace resins like BADGE-DDS. Mechanical testing, including tensile, flexural, and fracture toughness, demonstrated promising results, with VDE-DDS showing higher strength and modulus than BADGE-DDS. The flexural strength was considerably higher in particular. However, its hydrophilic nature led to higher water absorption, a challenge for long-term durability. For further testing, composite specimens were prepared using an autoclave.
Composite specimens reinforced with VDE-DDS displayed greater stiffness and strength under mechanical testing compared to BADGE-DDS in tests of in-plane shear strength, compression and inter-laminar shear strength tests, though BADGE-DDS composites outperformed in low-velocity impact resistance. The impact testing also revealed that BADGE-DDS samples had a higher damage initiation energy while VDE-DDS samples had a higher bending stiffness. Overall, VDE-DDS offers comparable, if not better, thermal and mechanical characteristics to BADGE-DDS. VDE, in summary, presents a compelling case as a potential bio-based alternative for structural aerospace applications. ...
This thesis investigates the viability of a vanillin-derived bio-based alternative, VDE (Vanillyl Alcohol Diglycidyl Ether), to be used in high-performance composites for aerospace applications. VDE monomer is derived from vanillin, which is obtained from lignin, a material present in 35% of woody plants. The VDE-DDS resin system, when cured, exhibited comparable thermal and physical properties, such as glass transition temperature and heat deflection temperature, to traditional aerospace resins like BADGE-DDS. Mechanical testing, including tensile, flexural, and fracture toughness, demonstrated promising results, with VDE-DDS showing higher strength and modulus than BADGE-DDS. The flexural strength was considerably higher in particular. However, its hydrophilic nature led to higher water absorption, a challenge for long-term durability. For further testing, composite specimens were prepared using an autoclave.
Composite specimens reinforced with VDE-DDS displayed greater stiffness and strength under mechanical testing compared to BADGE-DDS in tests of in-plane shear strength, compression and inter-laminar shear strength tests, though BADGE-DDS composites outperformed in low-velocity impact resistance. The impact testing also revealed that BADGE-DDS samples had a higher damage initiation energy while VDE-DDS samples had a higher bending stiffness. Overall, VDE-DDS offers comparable, if not better, thermal and mechanical characteristics to BADGE-DDS. VDE, in summary, presents a compelling case as a potential bio-based alternative for structural aerospace applications. ...
The aerospace sector continues to drive innovations in high-performance materials. These materials however, tend to have energy intensive and emission heavy manufacturing processes. One of the most commonly used materials in aircrafts today are polymer matrix composites consisting of reinforcement fibers and a matrix. While the fibers provide the most strength to the composite, the matrix holds the fibers together and transfers the loads to them. The most commonly used matrix material today is made of BADGE (Bisphenol A Diglycidyl Ether), a material which is toxic to humans and comes from fossil-based products.
This thesis investigates the viability of a vanillin-derived bio-based alternative, VDE (Vanillyl Alcohol Diglycidyl Ether), to be used in high-performance composites for aerospace applications. VDE monomer is derived from vanillin, which is obtained from lignin, a material present in 35% of woody plants. The VDE-DDS resin system, when cured, exhibited comparable thermal and physical properties, such as glass transition temperature and heat deflection temperature, to traditional aerospace resins like BADGE-DDS. Mechanical testing, including tensile, flexural, and fracture toughness, demonstrated promising results, with VDE-DDS showing higher strength and modulus than BADGE-DDS. The flexural strength was considerably higher in particular. However, its hydrophilic nature led to higher water absorption, a challenge for long-term durability. For further testing, composite specimens were prepared using an autoclave.
Composite specimens reinforced with VDE-DDS displayed greater stiffness and strength under mechanical testing compared to BADGE-DDS in tests of in-plane shear strength, compression and inter-laminar shear strength tests, though BADGE-DDS composites outperformed in low-velocity impact resistance. The impact testing also revealed that BADGE-DDS samples had a higher damage initiation energy while VDE-DDS samples had a higher bending stiffness. Overall, VDE-DDS offers comparable, if not better, thermal and mechanical characteristics to BADGE-DDS. VDE, in summary, presents a compelling case as a potential bio-based alternative for structural aerospace applications.
This thesis investigates the viability of a vanillin-derived bio-based alternative, VDE (Vanillyl Alcohol Diglycidyl Ether), to be used in high-performance composites for aerospace applications. VDE monomer is derived from vanillin, which is obtained from lignin, a material present in 35% of woody plants. The VDE-DDS resin system, when cured, exhibited comparable thermal and physical properties, such as glass transition temperature and heat deflection temperature, to traditional aerospace resins like BADGE-DDS. Mechanical testing, including tensile, flexural, and fracture toughness, demonstrated promising results, with VDE-DDS showing higher strength and modulus than BADGE-DDS. The flexural strength was considerably higher in particular. However, its hydrophilic nature led to higher water absorption, a challenge for long-term durability. For further testing, composite specimens were prepared using an autoclave.
Composite specimens reinforced with VDE-DDS displayed greater stiffness and strength under mechanical testing compared to BADGE-DDS in tests of in-plane shear strength, compression and inter-laminar shear strength tests, though BADGE-DDS composites outperformed in low-velocity impact resistance. The impact testing also revealed that BADGE-DDS samples had a higher damage initiation energy while VDE-DDS samples had a higher bending stiffness. Overall, VDE-DDS offers comparable, if not better, thermal and mechanical characteristics to BADGE-DDS. VDE, in summary, presents a compelling case as a potential bio-based alternative for structural aerospace applications.
Manufacturing deviations in Hydrofoils and their impact on performance
Investigating the Manufacturing deviations of the Nacra 17 Hydrofoil and their impact on performance
The Nacra 17 is a foiling catamaran selected to compete in the 2024 Olympic Games. The Nacra 17 is a one-design class, which requires all equipment to be identical. The Dutch Olympic team found through testing the bending stiffness that there is a slight difference in how each of their hydrofoils performed. The question was asked: What are the manufacturing deviations in the Nacra 17 hydrofoils and how do they impact the performance? This research aims to answer the previously stated question. The 3D scanned hydrofoils validated that there is indeed a measurable difference in shape between the different hydrofoils of the Olympic team. A successful method was proposed that automatically extracts 2D profile section properties from the point-cloud data of a 3D scanned hydrofoil. This method used a rough orientation using the profile plotted in polar coordinates. The mean camber line could be extracted using the Voronoi vertex points and the offset of the profile surface. The resulting data set was fitted using non-periodic cubic B-spline curves. This produced a curve for the mean camber line and the thickness profile. Comparison of profile properties resulted in the conclusion that profile thickness (yt) could show that the two female mould halves were probably spaced differently for the different hydrofoils by a standard deviation of 0.0669 mm at a thickness of 22.6 mm. Differences are found in the maximum thickness location (xt), Leading edge radius (rle), maximum camber (yc) and its location (xc). However, the differences in lift over drag for the different hydrofoils are minimal. The size of the drag bucket did not differ more than 0.1 of the lift coefficient (cl) for the same drag coefficient. With the exception of in general one section that presented an early separation. The specific profile showing early separation changes along the span, not allowing for the generalisation for the complete hydrofoil. It shows that the curvature at the leading edge of the profile is critical for the performance of the Nacra hydrofoil. Knowing which part of the profile shape is critical. Companies can take this area into account when designing the production process for the next hydrofoil, and the Olympic team can focus on maintaining these areas of the hydrofoil. Allowing the best preparation to be competitive at the next Olympic games.
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The Nacra 17 is a foiling catamaran selected to compete in the 2024 Olympic Games. The Nacra 17 is a one-design class, which requires all equipment to be identical. The Dutch Olympic team found through testing the bending stiffness that there is a slight difference in how each of their hydrofoils performed. The question was asked: What are the manufacturing deviations in the Nacra 17 hydrofoils and how do they impact the performance? This research aims to answer the previously stated question. The 3D scanned hydrofoils validated that there is indeed a measurable difference in shape between the different hydrofoils of the Olympic team. A successful method was proposed that automatically extracts 2D profile section properties from the point-cloud data of a 3D scanned hydrofoil. This method used a rough orientation using the profile plotted in polar coordinates. The mean camber line could be extracted using the Voronoi vertex points and the offset of the profile surface. The resulting data set was fitted using non-periodic cubic B-spline curves. This produced a curve for the mean camber line and the thickness profile. Comparison of profile properties resulted in the conclusion that profile thickness (yt) could show that the two female mould halves were probably spaced differently for the different hydrofoils by a standard deviation of 0.0669 mm at a thickness of 22.6 mm. Differences are found in the maximum thickness location (xt), Leading edge radius (rle), maximum camber (yc) and its location (xc). However, the differences in lift over drag for the different hydrofoils are minimal. The size of the drag bucket did not differ more than 0.1 of the lift coefficient (cl) for the same drag coefficient. With the exception of in general one section that presented an early separation. The specific profile showing early separation changes along the span, not allowing for the generalisation for the complete hydrofoil. It shows that the curvature at the leading edge of the profile is critical for the performance of the Nacra hydrofoil. Knowing which part of the profile shape is critical. Companies can take this area into account when designing the production process for the next hydrofoil, and the Olympic team can focus on maintaining these areas of the hydrofoil. Allowing the best preparation to be competitive at the next Olympic games.
Fibre metal laminates (FML) were initially conceived as a hybrid material, aiming to create synergy between the impact resistance of metals and excellent fatigue resistance of fibre reinforced polymers. The purpose of this approach was to overcome the limitations of single-material structures. However, despite its considerable promise, the use of the FML concept has primarily been confined to aerospace applications and heavily relies on synthetic fibres that carry significant environmental implications. Hence, given the growing concerns about climate change and the challenges posed by recycling glass fibre composites, a new generation of FMLs with a reduced carbon footprint should be envisaged.
Research on flax fibre composites reveals convincing mechanical properties and remarkable damping capacities. However, the broader adoption of these composites remains restricted primarily due to issues related to low impact resistance, moisture absorption and flammability concerns. The FML concept presents a viable solution to surmount these constraints, consequently facilitating the integration of these materials into primary structures. Hence, the research endeavour aimed to attain comprehensive insights into FLAx REinforced aluminium (FLARE), particularly focusing on its impact resistance and vibration damping capabilities, which are believed to be the principal benefits of this hybrid material.
The research goal was divided into three distinct research tasks: conducting experimental analyses to characterise the damping behaviour of FLARE, evaluating the impact resistance through experimental means, and validating predictive tools to offer initial insights into the design principles governing such a FML. FLARE, along with flax fibre reinforced epoxy (FFRE) and GLARE specimens, were manufactured using wet layup combined with vacuum bagging techniques.
First, tensile tests were conducted to validate the applicability of the metal volume fraction (MVF) approach in predicting the mechanical properties of FLARE. Intriguingly, the well-known non-linear behaviour exhibited by flax was not observed in the case of FLARE. The results revealed that while the MVF method provided a satisfactory approximation, it was the "inelastic" modulus of FFRE that predominantly contributed to the stiffness of FLARE.
Dynamic mechanical analysis and vibration beam tests were carried out to assess the influence of incorporating metallic layers on the vibration damping characteristics of flax fibre composites. The investigation revealed that the metallic layer predominantly governs the damping behaviour of the FML. Notably, an inverse rule of mixture emerged as the most effective means of approximating its loss factor.
Low-velocity impact tests were conducted to gain insights into the impact response of FLARE in comparison to conventional FMLs. The analysis indicated that the aluminium layers play a significant role in energy absorption, whereas the composite strength emerges as the critical factor influencing impact resistance. A quasi-static analytical model was also assessed, offering an initial estimation of the impact response, yet it warrants further refinement.
In conclusion, the FML concept holds promise for FLARE, but its application requires a novel approach compared to previous methods, to render FLARE viable for practical real-world applications. ...
Research on flax fibre composites reveals convincing mechanical properties and remarkable damping capacities. However, the broader adoption of these composites remains restricted primarily due to issues related to low impact resistance, moisture absorption and flammability concerns. The FML concept presents a viable solution to surmount these constraints, consequently facilitating the integration of these materials into primary structures. Hence, the research endeavour aimed to attain comprehensive insights into FLAx REinforced aluminium (FLARE), particularly focusing on its impact resistance and vibration damping capabilities, which are believed to be the principal benefits of this hybrid material.
The research goal was divided into three distinct research tasks: conducting experimental analyses to characterise the damping behaviour of FLARE, evaluating the impact resistance through experimental means, and validating predictive tools to offer initial insights into the design principles governing such a FML. FLARE, along with flax fibre reinforced epoxy (FFRE) and GLARE specimens, were manufactured using wet layup combined with vacuum bagging techniques.
First, tensile tests were conducted to validate the applicability of the metal volume fraction (MVF) approach in predicting the mechanical properties of FLARE. Intriguingly, the well-known non-linear behaviour exhibited by flax was not observed in the case of FLARE. The results revealed that while the MVF method provided a satisfactory approximation, it was the "inelastic" modulus of FFRE that predominantly contributed to the stiffness of FLARE.
Dynamic mechanical analysis and vibration beam tests were carried out to assess the influence of incorporating metallic layers on the vibration damping characteristics of flax fibre composites. The investigation revealed that the metallic layer predominantly governs the damping behaviour of the FML. Notably, an inverse rule of mixture emerged as the most effective means of approximating its loss factor.
Low-velocity impact tests were conducted to gain insights into the impact response of FLARE in comparison to conventional FMLs. The analysis indicated that the aluminium layers play a significant role in energy absorption, whereas the composite strength emerges as the critical factor influencing impact resistance. A quasi-static analytical model was also assessed, offering an initial estimation of the impact response, yet it warrants further refinement.
In conclusion, the FML concept holds promise for FLARE, but its application requires a novel approach compared to previous methods, to render FLARE viable for practical real-world applications. ...
Fibre metal laminates (FML) were initially conceived as a hybrid material, aiming to create synergy between the impact resistance of metals and excellent fatigue resistance of fibre reinforced polymers. The purpose of this approach was to overcome the limitations of single-material structures. However, despite its considerable promise, the use of the FML concept has primarily been confined to aerospace applications and heavily relies on synthetic fibres that carry significant environmental implications. Hence, given the growing concerns about climate change and the challenges posed by recycling glass fibre composites, a new generation of FMLs with a reduced carbon footprint should be envisaged.
Research on flax fibre composites reveals convincing mechanical properties and remarkable damping capacities. However, the broader adoption of these composites remains restricted primarily due to issues related to low impact resistance, moisture absorption and flammability concerns. The FML concept presents a viable solution to surmount these constraints, consequently facilitating the integration of these materials into primary structures. Hence, the research endeavour aimed to attain comprehensive insights into FLAx REinforced aluminium (FLARE), particularly focusing on its impact resistance and vibration damping capabilities, which are believed to be the principal benefits of this hybrid material.
The research goal was divided into three distinct research tasks: conducting experimental analyses to characterise the damping behaviour of FLARE, evaluating the impact resistance through experimental means, and validating predictive tools to offer initial insights into the design principles governing such a FML. FLARE, along with flax fibre reinforced epoxy (FFRE) and GLARE specimens, were manufactured using wet layup combined with vacuum bagging techniques.
First, tensile tests were conducted to validate the applicability of the metal volume fraction (MVF) approach in predicting the mechanical properties of FLARE. Intriguingly, the well-known non-linear behaviour exhibited by flax was not observed in the case of FLARE. The results revealed that while the MVF method provided a satisfactory approximation, it was the "inelastic" modulus of FFRE that predominantly contributed to the stiffness of FLARE.
Dynamic mechanical analysis and vibration beam tests were carried out to assess the influence of incorporating metallic layers on the vibration damping characteristics of flax fibre composites. The investigation revealed that the metallic layer predominantly governs the damping behaviour of the FML. Notably, an inverse rule of mixture emerged as the most effective means of approximating its loss factor.
Low-velocity impact tests were conducted to gain insights into the impact response of FLARE in comparison to conventional FMLs. The analysis indicated that the aluminium layers play a significant role in energy absorption, whereas the composite strength emerges as the critical factor influencing impact resistance. A quasi-static analytical model was also assessed, offering an initial estimation of the impact response, yet it warrants further refinement.
In conclusion, the FML concept holds promise for FLARE, but its application requires a novel approach compared to previous methods, to render FLARE viable for practical real-world applications.
Research on flax fibre composites reveals convincing mechanical properties and remarkable damping capacities. However, the broader adoption of these composites remains restricted primarily due to issues related to low impact resistance, moisture absorption and flammability concerns. The FML concept presents a viable solution to surmount these constraints, consequently facilitating the integration of these materials into primary structures. Hence, the research endeavour aimed to attain comprehensive insights into FLAx REinforced aluminium (FLARE), particularly focusing on its impact resistance and vibration damping capabilities, which are believed to be the principal benefits of this hybrid material.
The research goal was divided into three distinct research tasks: conducting experimental analyses to characterise the damping behaviour of FLARE, evaluating the impact resistance through experimental means, and validating predictive tools to offer initial insights into the design principles governing such a FML. FLARE, along with flax fibre reinforced epoxy (FFRE) and GLARE specimens, were manufactured using wet layup combined with vacuum bagging techniques.
First, tensile tests were conducted to validate the applicability of the metal volume fraction (MVF) approach in predicting the mechanical properties of FLARE. Intriguingly, the well-known non-linear behaviour exhibited by flax was not observed in the case of FLARE. The results revealed that while the MVF method provided a satisfactory approximation, it was the "inelastic" modulus of FFRE that predominantly contributed to the stiffness of FLARE.
Dynamic mechanical analysis and vibration beam tests were carried out to assess the influence of incorporating metallic layers on the vibration damping characteristics of flax fibre composites. The investigation revealed that the metallic layer predominantly governs the damping behaviour of the FML. Notably, an inverse rule of mixture emerged as the most effective means of approximating its loss factor.
Low-velocity impact tests were conducted to gain insights into the impact response of FLARE in comparison to conventional FMLs. The analysis indicated that the aluminium layers play a significant role in energy absorption, whereas the composite strength emerges as the critical factor influencing impact resistance. A quasi-static analytical model was also assessed, offering an initial estimation of the impact response, yet it warrants further refinement.
In conclusion, the FML concept holds promise for FLARE, but its application requires a novel approach compared to previous methods, to render FLARE viable for practical real-world applications.