B. Chen
Please Note
23 records found
1
The analytical methods showed strong agreement with local J-integral results across a range of load cases, with errors typically below 2% of the fracture toughness. Increased stiffness in the multilayer model lengthened the cohesive zone and improved accuracy by aligning more closely with the analytical assumptions. In the residual stress model, the auxiliary problem, free of residual stresses, accurately reproduced the real problem’s crack plane opening profiles for variations in temperature, stiffness, thermal expansion coefficient, and mechanical loading. Validating the analytical expressions for the auxiliary case--combined with opening profile consistency and the assumption of a potential-function-based J-integral--validated their applicability to the real problem.
These results confirm that the analytical J-integral formulations can accurately estimate the energy release rate when material properties are unknown and residual stresses are present, enabling reliable structural integrity assessments of composite structures. ...
The analytical methods showed strong agreement with local J-integral results across a range of load cases, with errors typically below 2% of the fracture toughness. Increased stiffness in the multilayer model lengthened the cohesive zone and improved accuracy by aligning more closely with the analytical assumptions. In the residual stress model, the auxiliary problem, free of residual stresses, accurately reproduced the real problem’s crack plane opening profiles for variations in temperature, stiffness, thermal expansion coefficient, and mechanical loading. Validating the analytical expressions for the auxiliary case--combined with opening profile consistency and the assumption of a potential-function-based J-integral--validated their applicability to the real problem.
These results confirm that the analytical J-integral formulations can accurately estimate the energy release rate when material properties are unknown and residual stresses are present, enabling reliable structural integrity assessments of composite structures.
On the intersection of quantum computing and computational structural mechanics
With a focus on near-term quantum computing
This thesis studies the introduction of quantum-accellerated computing in structural mechanics, a field that traditionally leverages computational techniques at both industrial and research scales. The scope is limited to practical and mostly near-term quantum computing. Therefore, the algorithms analyzed or proposed are evaluated for their runtime as end-to-end routines and for their ability to run on near-term quantum devices.
Given the vastness of the application domain, the research was developed in three separate threads. The first is a review of quantum algorithms applicable to partial differential equations (PDEs) in structural mechanics. The second is an application of a variational quantum algorithm for linear systems of equations to the discrete Poisson equation, while the last studies how quantum machine learning, specifically quantum kernel methods, discriminates damage-inducing loading states in a composite plate with a cutout.
Each of the three parts reveals the potentials and limitations of practical quantum-accelerated computing.
The PDE review questions the end-to-end advantage of fault-tolerant quantum algorithms and highlights the need to specialize near-term alternatives to problems in mechanics.
The work on the variational quantum linear solver emphasizes the matrix decomposition bottleneck and proposes a method to factorize the discrete Poisson equation matrix.
Finally, the work on kernel methods for damage identification shows how heuristically selected and trained quantum kernels reach scores comparable to classical best-practice kernels, but also hints at the fact that potential quantum advantage requires more systematic kernel optimization and retaining performance when scaling quantum systems beyond classical simulation. ...
This thesis studies the introduction of quantum-accellerated computing in structural mechanics, a field that traditionally leverages computational techniques at both industrial and research scales. The scope is limited to practical and mostly near-term quantum computing. Therefore, the algorithms analyzed or proposed are evaluated for their runtime as end-to-end routines and for their ability to run on near-term quantum devices.
Given the vastness of the application domain, the research was developed in three separate threads. The first is a review of quantum algorithms applicable to partial differential equations (PDEs) in structural mechanics. The second is an application of a variational quantum algorithm for linear systems of equations to the discrete Poisson equation, while the last studies how quantum machine learning, specifically quantum kernel methods, discriminates damage-inducing loading states in a composite plate with a cutout.
Each of the three parts reveals the potentials and limitations of practical quantum-accelerated computing.
The PDE review questions the end-to-end advantage of fault-tolerant quantum algorithms and highlights the need to specialize near-term alternatives to problems in mechanics.
The work on the variational quantum linear solver emphasizes the matrix decomposition bottleneck and proposes a method to factorize the discrete Poisson equation matrix.
Finally, the work on kernel methods for damage identification shows how heuristically selected and trained quantum kernels reach scores comparable to classical best-practice kernels, but also hints at the fact that potential quantum advantage requires more systematic kernel optimization and retaining performance when scaling quantum systems beyond classical simulation.
Finite element modelling of fibre matrix debonding and frictional sliding and their effects on neighbouring fibres
European Wind Energy Master Thesis
Abaqus, with particular attention given to their influence on neighbouring fibres. It aims to improve model accuracy through advanced simulations and validation methods. A literature review underscores the need for robust finite element models in predicting composite material behaviour in fatigue. Theoretical equations for validating the finite element model are developed.
Single-fibre and multi-fibre models are utilised, with the former being used primarily for validation and the latter being used to simulate various realistic cases. Results demonstrate successful validation and provide insights into the effects of friction along the debond interface on stress concentrations in neighbouring fibres. Key findings indicate that reducing interfacial friction increases crack tip energy release rates, leading to stress fields that could potentially cause fractures in neighbouring fibres near the debond crack tip. ...
Abaqus, with particular attention given to their influence on neighbouring fibres. It aims to improve model accuracy through advanced simulations and validation methods. A literature review underscores the need for robust finite element models in predicting composite material behaviour in fatigue. Theoretical equations for validating the finite element model are developed.
Single-fibre and multi-fibre models are utilised, with the former being used primarily for validation and the latter being used to simulate various realistic cases. Results demonstrate successful validation and provide insights into the effects of friction along the debond interface on stress concentrations in neighbouring fibres. Key findings indicate that reducing interfacial friction increases crack tip energy release rates, leading to stress fields that could potentially cause fractures in neighbouring fibres near the debond crack tip.
Progressive Damage Analysis of Tapered Composite Laminates
A Systematic Approach to Predict Damage Arrest
This research investigates progressive failure analysis in notched composite laminates, with a particular focus on simulating stable damage growth and arrest within the transition region of tapered laminates. A multi-fidelity modelling approach was adopted using flat laminates as a baseline for evaluating damage growth behaviour in the transition regions. Consistent ply stack orientations in both tapered and flat laminates allow for direct comparisons of their distinct failure behaviours. The methodology includes a low-fidelity model that utilizes cohesive elements to simulate self-similar crack growth initiating from notch tips. For more detailed predictions, a high-fidelity model incorporating a discrete ply-by-ply approach with cohesive interactions was used to capture both intra-laminar and inter-laminar damage mechanisms. In this high-fidelity approach, two intralaminar damage models are compared: a user-defined continuum damage model (VUMAT) and a built-in Hashin damage model available in ABAQUS. The VUMAT model applies specific softening laws and element sizes for each failure mode to ensure accurate energy dissipation, while the Hashin model serves as a simpler built-in alternative.
The results show that, despite simplifications, low-fidelity models provide reasonable estimates of failure loads and stiffness in the elastic region, aligning closely with high-fidelity models and existing experimental data. The high-fidelity model effectively captures complex damage modes, with the VUMAT model outperforming the Hashin model in accuracy. The global-local approach proves reliable, offering results comparable to a globally refined meshing approach. It shows potential for use in analyzing larger, computationally demanding structures. Overall, the findings also highlight the importance of fibre-aligned meshing and precise cohesive zone modelling in predicting damage initiation and progression in notched composite laminates, providing insights for designing damage-tolerant composite structures.
...
This research investigates progressive failure analysis in notched composite laminates, with a particular focus on simulating stable damage growth and arrest within the transition region of tapered laminates. A multi-fidelity modelling approach was adopted using flat laminates as a baseline for evaluating damage growth behaviour in the transition regions. Consistent ply stack orientations in both tapered and flat laminates allow for direct comparisons of their distinct failure behaviours. The methodology includes a low-fidelity model that utilizes cohesive elements to simulate self-similar crack growth initiating from notch tips. For more detailed predictions, a high-fidelity model incorporating a discrete ply-by-ply approach with cohesive interactions was used to capture both intra-laminar and inter-laminar damage mechanisms. In this high-fidelity approach, two intralaminar damage models are compared: a user-defined continuum damage model (VUMAT) and a built-in Hashin damage model available in ABAQUS. The VUMAT model applies specific softening laws and element sizes for each failure mode to ensure accurate energy dissipation, while the Hashin model serves as a simpler built-in alternative.
The results show that, despite simplifications, low-fidelity models provide reasonable estimates of failure loads and stiffness in the elastic region, aligning closely with high-fidelity models and existing experimental data. The high-fidelity model effectively captures complex damage modes, with the VUMAT model outperforming the Hashin model in accuracy. The global-local approach proves reliable, offering results comparable to a globally refined meshing approach. It shows potential for use in analyzing larger, computationally demanding structures. Overall, the findings also highlight the importance of fibre-aligned meshing and precise cohesive zone modelling in predicting damage initiation and progression in notched composite laminates, providing insights for designing damage-tolerant composite structures.
During an explosion, the energy released from the blast will be absorbed by the composite material. This often results in the delamination of plies within the laminate. Due to the delamination, bending loads will be taken over by membrane loads. This is proven advantageous for composite materials as they are stronger in membrane loading.
Unfortunately, modelling sizeable composite structures with a Direct Numerical Simulation (DNS) requires the use of a lot of elements. This, in turn, results in long computational times, particularly for non-linear analyses. Multiscale modelling is a possible solution to this problem.
This study explores the method of Computational Homogenisation for delamination in composite laminates as an alternative to 3D DNS modelling. Two-dimensional Shell-Interface-Shell elements (SIFS elements) are introduced on the macroscale. These double-layered shell elements consist of two stacked Mindlin-Reissner shell elements with an interface element connecting the two shells. Each integration point of a SIFS element is linked to a mesoscopic 3D coupled Representative Volume Element (cRVE), which is also split into two shells with an interface in between. By applying linear and periodic boundary conditions that incorporate the macroscopic strains on the cRVE, mesoscopic stresses are determined, leading to macroscopic stresses and the macroscopic stiffness matrix.
The proposed multiscale framework is validated by a set of load cases with different ply configurations. The results are then compared to those of a 3D DNS. The multiscale framework performs reasonably well; however, it is not without its limitations. Firstly, the cRVE exhibits width dependence, requiring the implementation of a sufficiently narrow cRVE for accurate results. Additionally, SIFS elements may lack kinematic consistency with 3D solid elements, constraining certain deformations and resulting in overly stiff responses for SIFS analyses. The proposed multiscale framework might not perform as accurately as the 3D DNS in specific load cases, one of which is explored in this work.
Returning to the original goal of this work for the multiscale model, certain extensions still need to be implemented to design composite laminates for blast protection. Implementation of the arc-length method will provide insight into snapback behaviour that could occur during loading. Next, the macroscale and mesoscale models need to be adapted for multiple delaminations over the height of a laminate. Furthermore, the implementation of dynamic loading is a necessary step, as blast loads induce strong dynamic behaviour. Finally, the integration of Artificial Intelligence / Machine Learning into the framework could improve the model by further reducing computational time. ...
During an explosion, the energy released from the blast will be absorbed by the composite material. This often results in the delamination of plies within the laminate. Due to the delamination, bending loads will be taken over by membrane loads. This is proven advantageous for composite materials as they are stronger in membrane loading.
Unfortunately, modelling sizeable composite structures with a Direct Numerical Simulation (DNS) requires the use of a lot of elements. This, in turn, results in long computational times, particularly for non-linear analyses. Multiscale modelling is a possible solution to this problem.
This study explores the method of Computational Homogenisation for delamination in composite laminates as an alternative to 3D DNS modelling. Two-dimensional Shell-Interface-Shell elements (SIFS elements) are introduced on the macroscale. These double-layered shell elements consist of two stacked Mindlin-Reissner shell elements with an interface element connecting the two shells. Each integration point of a SIFS element is linked to a mesoscopic 3D coupled Representative Volume Element (cRVE), which is also split into two shells with an interface in between. By applying linear and periodic boundary conditions that incorporate the macroscopic strains on the cRVE, mesoscopic stresses are determined, leading to macroscopic stresses and the macroscopic stiffness matrix.
The proposed multiscale framework is validated by a set of load cases with different ply configurations. The results are then compared to those of a 3D DNS. The multiscale framework performs reasonably well; however, it is not without its limitations. Firstly, the cRVE exhibits width dependence, requiring the implementation of a sufficiently narrow cRVE for accurate results. Additionally, SIFS elements may lack kinematic consistency with 3D solid elements, constraining certain deformations and resulting in overly stiff responses for SIFS analyses. The proposed multiscale framework might not perform as accurately as the 3D DNS in specific load cases, one of which is explored in this work.
Returning to the original goal of this work for the multiscale model, certain extensions still need to be implemented to design composite laminates for blast protection. Implementation of the arc-length method will provide insight into snapback behaviour that could occur during loading. Next, the macroscale and mesoscale models need to be adapted for multiple delaminations over the height of a laminate. Furthermore, the implementation of dynamic loading is a necessary step, as blast loads induce strong dynamic behaviour. Finally, the integration of Artificial Intelligence / Machine Learning into the framework could improve the model by further reducing computational time.
Multiple simulation campaigns were performed to analyze this variability on a single solder joint level as well as on a product level. A number of sample products with random combinations of unique solder joints were developed for the latter campaign. ...
Multiple simulation campaigns were performed to analyze this variability on a single solder joint level as well as on a product level. A number of sample products with random combinations of unique solder joints were developed for the latter campaign.
Burst Pressure Prediction of Cord-Rubber Composite Pressure Vessels
Using Global-Local Nonlinear Finite Element Analysis
Cord-reinforced rubber composites are used in several safety-critical industries such as oil and gas and civil plumbing. Despite their widespread use, limited research is available that focuses on the single-cycle damage phenomenon that may occur in events such as over-pressurization.
The aim of this project is to close this knowledge gap by developing a theory that accounts for the key damage modes present in CRC structures. This involves experimental studies for material characterization and identification of relevant damage modes, the creation of a novel fibre overlap model that accurately replicates the meso-level filament-wound structure, and translation of the experimentally verified damage modes into functional damage initiation and propagation laws using a global-local FEA model. Verification of the created damage model is done experimentally on samples manufactured and tested at TANIQ, with differences between model predictions and experimental burst pressures being $\approx 6.5\%$. This is a marked improvement over Taniq's current FEA model, which overpredicts the solution by $\approx 27\%$.
The successful implementation of this model would help industries like TANIQ build efficient, strong, and lightweight rubber composite parts for various industries, thus adapting aerospace design principles to the development of more commonplace apparatus.
...
Cord-reinforced rubber composites are used in several safety-critical industries such as oil and gas and civil plumbing. Despite their widespread use, limited research is available that focuses on the single-cycle damage phenomenon that may occur in events such as over-pressurization.
The aim of this project is to close this knowledge gap by developing a theory that accounts for the key damage modes present in CRC structures. This involves experimental studies for material characterization and identification of relevant damage modes, the creation of a novel fibre overlap model that accurately replicates the meso-level filament-wound structure, and translation of the experimentally verified damage modes into functional damage initiation and propagation laws using a global-local FEA model. Verification of the created damage model is done experimentally on samples manufactured and tested at TANIQ, with differences between model predictions and experimental burst pressures being $\approx 6.5\%$. This is a marked improvement over Taniq's current FEA model, which overpredicts the solution by $\approx 27\%$.
The successful implementation of this model would help industries like TANIQ build efficient, strong, and lightweight rubber composite parts for various industries, thus adapting aerospace design principles to the development of more commonplace apparatus.
A practical quantum algorithm for solving structural optimization problems
A proof-of-concept!
...
The Neuromorphic Element: A Data-Driven Finite Element Formulation Using Self-Designing Neural Networks
Proof of Concept on Nonlinear Trusses
explore how quantum computing can be used to aid in solving structural optimization problems. Two methods are developed with which simple 2-dimensional truss systems can be optimized using the D-Wave quantum annealer. The methods aim to find the most lightweight choices for the truss cross-sectional areas while complying with material limit stress constraints. The first method directly casts such an optimization problem into a QUBO format. However, due to difficulties with formulating the stress constraint, this method was found to produce a trivial optimization problem. The second method attempts to symbolically solve a truss finite-element problem, using the resulting symbolic expressions to set up an optimization objective function. Although these objective functions are confirmed to work via classical brute-force analysis, the quantum annealer is shown to have difficulty finding the global optimum solution for truss systems with three or more elements. These results indicate that it is not currently beneficial to use quantum annealing for these structural optimization problems. Nevertheless, some improvements to the method for setting up the objective functions are suggested. The next generation of quantum annealers is expected to perform better for these practical applications, potentially becoming a useful tool in the engineering toolbox. ...
explore how quantum computing can be used to aid in solving structural optimization problems. Two methods are developed with which simple 2-dimensional truss systems can be optimized using the D-Wave quantum annealer. The methods aim to find the most lightweight choices for the truss cross-sectional areas while complying with material limit stress constraints. The first method directly casts such an optimization problem into a QUBO format. However, due to difficulties with formulating the stress constraint, this method was found to produce a trivial optimization problem. The second method attempts to symbolically solve a truss finite-element problem, using the resulting symbolic expressions to set up an optimization objective function. Although these objective functions are confirmed to work via classical brute-force analysis, the quantum annealer is shown to have difficulty finding the global optimum solution for truss systems with three or more elements. These results indicate that it is not currently beneficial to use quantum annealing for these structural optimization problems. Nevertheless, some improvements to the method for setting up the objective functions are suggested. The next generation of quantum annealers is expected to perform better for these practical applications, potentially becoming a useful tool in the engineering toolbox.
Data for training and evaluating these neural networks was first generated through 20 finite element models solved using Abaqus 2017. Standard neural networks trained to directly reproduce these damage patterns, as well as reduced-image neural networks trained to reproduce a reduced formof these patterns (obtained using convolutional neural networks) were analysed, and both were found in want ofmore training data. The generation of a further 421 finite element models resulted in a striking improvement in the performance of both networks, but with the standard neural network outperforming the reduce-image neural network. Thereafter, it was discovered that a hybrid network that combined facets of the standard and convolutional neural networks performed superior to both.
In the process of training these networks, it was recognised that while the performance metrics served as an indicator of the resemblance between the predicted and actual outputs in terms of colours and contours, the same trends did not apply to the image quality. In order to improve the visual quality of outputs from the hybrid network, the use of the Structural Similarity Index (SSIM) was explored. It was eventually determined that pre-training the network using the Mean Square Error (MSE) as its optimising metric before then doing the final training using SSIM resulted in a model with impressive results. This fine-tuned model carried out predictions with a mean error of 0.0014 on theMSE metric and 0.9804 on the SSIM metric when evaluated on an independent dataset. Finally, the reliability and computational efficiency of the hybrid model was measured. It was found that approximately 95% of the MSE values on the independent dataset were within a value of 0.0040, while the same percentage of SSIM values were over 0.9100. The computation speed, meanwhile, improved by a factor of roughly 34 times on average, with the figure rising to over 443 on specific models. ...
Data for training and evaluating these neural networks was first generated through 20 finite element models solved using Abaqus 2017. Standard neural networks trained to directly reproduce these damage patterns, as well as reduced-image neural networks trained to reproduce a reduced formof these patterns (obtained using convolutional neural networks) were analysed, and both were found in want ofmore training data. The generation of a further 421 finite element models resulted in a striking improvement in the performance of both networks, but with the standard neural network outperforming the reduce-image neural network. Thereafter, it was discovered that a hybrid network that combined facets of the standard and convolutional neural networks performed superior to both.
In the process of training these networks, it was recognised that while the performance metrics served as an indicator of the resemblance between the predicted and actual outputs in terms of colours and contours, the same trends did not apply to the image quality. In order to improve the visual quality of outputs from the hybrid network, the use of the Structural Similarity Index (SSIM) was explored. It was eventually determined that pre-training the network using the Mean Square Error (MSE) as its optimising metric before then doing the final training using SSIM resulted in a model with impressive results. This fine-tuned model carried out predictions with a mean error of 0.0014 on theMSE metric and 0.9804 on the SSIM metric when evaluated on an independent dataset. Finally, the reliability and computational efficiency of the hybrid model was measured. It was found that approximately 95% of the MSE values on the independent dataset were within a value of 0.0040, while the same percentage of SSIM values were over 0.9100. The computation speed, meanwhile, improved by a factor of roughly 34 times on average, with the figure rising to over 443 on specific models.
C1 Cohesive Element Models for 3D Delamination
Towards overcoming the mesh density constraint in FE delamination analyses
current models to capture the deformation of the delaminating substrates. The present work focuses on the implementation and testing of triangular thin plate substrate elements and compatible cohesive elements, which satisfy C1-continuity at their boundary. The improved regularity meets the continuity requirement coming from the Kirchhoff Plate Theory and the triangular shape allows for conformity to complex geometries. After verification of plate and
cohesive element singularly, the overall model is validated for mode I delamination. Very accurate predictions of the limit load and crack propagation phase are found, using CEs as large as 11 times the cohesive zone. ...
current models to capture the deformation of the delaminating substrates. The present work focuses on the implementation and testing of triangular thin plate substrate elements and compatible cohesive elements, which satisfy C1-continuity at their boundary. The improved regularity meets the continuity requirement coming from the Kirchhoff Plate Theory and the triangular shape allows for conformity to complex geometries. After verification of plate and
cohesive element singularly, the overall model is validated for mode I delamination. Very accurate predictions of the limit load and crack propagation phase are found, using CEs as large as 11 times the cohesive zone.