We developed a semi-analytical fibre bundle model to simulate the longitudinal tensile failure of... more We developed a semi-analytical fibre bundle model to simulate the longitudinal tensile failure of large composite bundles of continuous fibres. The model uses shear-lag to calculate the stress recovery along broken fibres, and an efficient field superposition method to calculate the stress concentration on the intact fibres, which has been validated against analytical and FE results from the literature. The baseline version of the model uses static equilibrium stress states, and considers fibre failure driven by strength of materials (stress overload) as the only damage theory which can drive bundle failure. Like other models in the literature, the baseline model fails to capture the correct size effect (decreasing composite strength with bundle size) shown by experimental results. Two model variants have been developed which include dynamics stress concentrations (model DE) and a fracture mechanics (model FM) failure criterion respectively. To the knowledge of the authors, it is th...
INTRODUCTION MBSE aims to integrate engineering models across tools and domain boundaries to supp... more INTRODUCTION MBSE aims to integrate engineering models across tools and domain boundaries to support traditional systems engineering activities (e.g., requirements elicitation and traceability, design, analysis, verification and validation) [1], [2]. However, MBSE does not inherently solve interoperability with the multiple model-based infrastructures involved in a complex systems engineering project. The challenge is to implement digital continuity in the three dimensions of systems engineering: across disciplines, throughout the lifecycle, and along the supply chain [3]. Changes to the system requirements or the design must be propagated automatically through the supply chain to facilitate the swift evaluation of its impact. Documentation, where required, will be generated and updated automatically.
A new bio-inspired microstructure design approach was developed to improve the translaminar tough... more A new bio-inspired microstructure design approach was developed to improve the translaminar toughness and damage tolerance of Carbon Fibre Reinforced Plastic (CFRP) structures. The microstructure designs take inspiration from the microstructures of biological composites by adopting the most important toughening mechanisms, and applying them to CFRP laminates. Carefully placed patterns of laser-engraved micro-cuts are inserted in the microstructure of the laminate during the manufacturing process. These micro-cuts change the crack propagation path during translaminar fracture, hence allowing to engineer the fracture behaviour of the composite. The microstructure design approach led to remarkable improvements in the maximum tensile load (up to 189%) and translaminar work of fracture (up to 460%) during Compact Tension test for CFRP laminates with Cross-Ply and Quasi-Isotropic (QI) layups when compared with the corresponding un-modified laminates. Furthermore, a significant improvement...
We are developing a lightweight ceramic/polymer composite for km/s fragment resistance. It uses a... more We are developing a lightweight ceramic/polymer composite for km/s fragment resistance. It uses a fundamentally new physical process for energy absorption that complements the conventional forms of energy dissipation of fracture and plastic deformation. This composite comes into its own against very high impact velocities, being able to provide protection in shock regimes where conventional materials like kevlar and steel can be considered incompressible fluids with zero protection capabilities. This material can be used in rocket motor casings for increased IM compliance. It can absorb and dissipate energy extremely quickly (of the order of 100kJ/m2/μs). Crucially it limits shock lensing effects, augmenting current capabilities against blast and shaped fragments. The energy dissipation mechanism propagates at 7km/s inside the material and activates with minimal (<2%) overall strain of the structure. The design of the composite is flexible enough to be optimised for a range of pr...
A three-Dimensional (3D) Fibre Bundle Model (FBM) has been developed to simulate the longitudinal... more A three-Dimensional (3D) Fibre Bundle Model (FBM) has been developed to simulate the longitudinal tensile failure and predict the statistical strength distribution of CFRP bundles of dierent sizes. The model incorporates an original semi-analytical approach to determine the stress eld inside the bundle and to predict the evolution of the failure process. The present model can account for the eects of bre-matrix debonding, as well as the eect of the size of the cluster of broken bres on the stress recovery length and, in turn, on the bundle strength. The predictions from the model are shown to compare favourably with experimental results from the literature, thus demonstrating the suitability of the modelling approach.
Both discontinuous fiber-reinforced composites and hybrid composites show the potential to overco... more Both discontinuous fiber-reinforced composites and hybrid composites show the potential to overcome the stiffness-toughness dilemma that conventional fiber reinforced polymer composites suffer from. To fully utilize the advantages of discontinuities and hybridization, careful design of the configuration of discontinuities is required. In this paper, high-precision fiber cuts with a staggered pattern were introduced in the unidirectional carbon fiber layer of hybrid carbon fiber/self-reinforced polypropylene composites. This aimed to control the failure mechanisms, hence targeting a gradual failure in tension. The effect of the geometrical parameters of the patterns, including cut length, cut fraction and step length, were investigated. The tensile behavior of the hybrids was influenced by a combined effect of these three parameters. The hybrids exhibited three types of the failure behavior: 1) single fracture of the carbon fiber layer followed by single delamination growth, 2) carbo...
A bio-inspired micro-structure design technique was used to increase the translaminar fracture to... more A bio-inspired micro-structure design technique was used to increase the translaminar fracture toughness and the notch strength of Quasi Isotropic carbon fibre laminates. Patterns of laser-engraved micro-cuts were inserted in the micro-structure of the laminate to promote crack deflection and force the formation of large bundle pull-outs during crack propagation. The design of the patterns of microcuts was defined following the predictions of a newly developed Finite Fracture Mechanics criterion. The technique allowed to achieve a 20% increase in the laminate notched strength and an 190% increase in the laminate translaminar work of fracture when compared with the un-modified baseline material.
A semi-analytical Monte Carlo fibre bundle model was developed to investigate the role of dynamic... more A semi-analytical Monte Carlo fibre bundle model was developed to investigate the role of dynamic effects and fracture mechanics in the longitudinal tensile failure of fibre-reinforced composites. To the knowledge of the authors, it is the first time that both effects are implemented in a fibre bundle model through direct simulation. The formulation includes a field superposition method to calculate the stress concentration around broken fibres which captures the effect of clusters of broken fibres. The Monte Carlo process was optimized to allow the simulation of bundles with thousands of fibres. The comparison between the predicted bundle strengths and experimental data suggests that, although the dynamic stress concentration significantly decreases the bundle strength, the trend and magnitude of the size effects in large composite bundles can only be explained considering fracture mechanics as the failure mechanism.
Carefully-placed patterns of micro-cuts have been designed and then used to increase the translam... more Carefully-placed patterns of micro-cuts have been designed and then used to increase the translaminar work of fracture in thin-ply CFRP composite laminates. These patterns of micro-cuts are able to deviate a translaminar crack and force the formation of large bundle pull-outs. The technique led to a 68% increase in the laminate notched strength and a 460% increase in the laminate translaminar work of fracture when compared with the un-modied baseline material. Part of the improved performance was found to be due to the generated interaction of failure mechanisms between contiguous plies with dierent orientation; this process for generating interaction opens new possibilities for micro-structure design which will be explored in future works.
We developed a semi-analytical fibre bundle model to simulate the longitudinal tensile failure of... more We developed a semi-analytical fibre bundle model to simulate the longitudinal tensile failure of large composite bundles of continuous fibres. The model uses shear-lag to calculate the stress recovery along broken fibres, and an efficient field superposition method to calculate the stress concentration on the intact fibres, which has been validated against analytical and FE results from the literature. The baseline version of the model uses static equilibrium stress states, and considers fibre failure driven by strength of materials (stress overload) as the only damage theory which can drive bundle failure. Like other models in the literature, the baseline model fails to capture the correct size effect (decreasing composite strength with bundle size) shown by experimental results. Two model variants have been developed which include dynamics stress concentrations (model DE) and a fracture mechanics (model FM) failure criterion respectively. To the knowledge of the authors, it is th...
INTRODUCTION MBSE aims to integrate engineering models across tools and domain boundaries to supp... more INTRODUCTION MBSE aims to integrate engineering models across tools and domain boundaries to support traditional systems engineering activities (e.g., requirements elicitation and traceability, design, analysis, verification and validation) [1], [2]. However, MBSE does not inherently solve interoperability with the multiple model-based infrastructures involved in a complex systems engineering project. The challenge is to implement digital continuity in the three dimensions of systems engineering: across disciplines, throughout the lifecycle, and along the supply chain [3]. Changes to the system requirements or the design must be propagated automatically through the supply chain to facilitate the swift evaluation of its impact. Documentation, where required, will be generated and updated automatically.
A new bio-inspired microstructure design approach was developed to improve the translaminar tough... more A new bio-inspired microstructure design approach was developed to improve the translaminar toughness and damage tolerance of Carbon Fibre Reinforced Plastic (CFRP) structures. The microstructure designs take inspiration from the microstructures of biological composites by adopting the most important toughening mechanisms, and applying them to CFRP laminates. Carefully placed patterns of laser-engraved micro-cuts are inserted in the microstructure of the laminate during the manufacturing process. These micro-cuts change the crack propagation path during translaminar fracture, hence allowing to engineer the fracture behaviour of the composite. The microstructure design approach led to remarkable improvements in the maximum tensile load (up to 189%) and translaminar work of fracture (up to 460%) during Compact Tension test for CFRP laminates with Cross-Ply and Quasi-Isotropic (QI) layups when compared with the corresponding un-modified laminates. Furthermore, a significant improvement...
We are developing a lightweight ceramic/polymer composite for km/s fragment resistance. It uses a... more We are developing a lightweight ceramic/polymer composite for km/s fragment resistance. It uses a fundamentally new physical process for energy absorption that complements the conventional forms of energy dissipation of fracture and plastic deformation. This composite comes into its own against very high impact velocities, being able to provide protection in shock regimes where conventional materials like kevlar and steel can be considered incompressible fluids with zero protection capabilities. This material can be used in rocket motor casings for increased IM compliance. It can absorb and dissipate energy extremely quickly (of the order of 100kJ/m2/μs). Crucially it limits shock lensing effects, augmenting current capabilities against blast and shaped fragments. The energy dissipation mechanism propagates at 7km/s inside the material and activates with minimal (<2%) overall strain of the structure. The design of the composite is flexible enough to be optimised for a range of pr...
A three-Dimensional (3D) Fibre Bundle Model (FBM) has been developed to simulate the longitudinal... more A three-Dimensional (3D) Fibre Bundle Model (FBM) has been developed to simulate the longitudinal tensile failure and predict the statistical strength distribution of CFRP bundles of dierent sizes. The model incorporates an original semi-analytical approach to determine the stress eld inside the bundle and to predict the evolution of the failure process. The present model can account for the eects of bre-matrix debonding, as well as the eect of the size of the cluster of broken bres on the stress recovery length and, in turn, on the bundle strength. The predictions from the model are shown to compare favourably with experimental results from the literature, thus demonstrating the suitability of the modelling approach.
Both discontinuous fiber-reinforced composites and hybrid composites show the potential to overco... more Both discontinuous fiber-reinforced composites and hybrid composites show the potential to overcome the stiffness-toughness dilemma that conventional fiber reinforced polymer composites suffer from. To fully utilize the advantages of discontinuities and hybridization, careful design of the configuration of discontinuities is required. In this paper, high-precision fiber cuts with a staggered pattern were introduced in the unidirectional carbon fiber layer of hybrid carbon fiber/self-reinforced polypropylene composites. This aimed to control the failure mechanisms, hence targeting a gradual failure in tension. The effect of the geometrical parameters of the patterns, including cut length, cut fraction and step length, were investigated. The tensile behavior of the hybrids was influenced by a combined effect of these three parameters. The hybrids exhibited three types of the failure behavior: 1) single fracture of the carbon fiber layer followed by single delamination growth, 2) carbo...
A bio-inspired micro-structure design technique was used to increase the translaminar fracture to... more A bio-inspired micro-structure design technique was used to increase the translaminar fracture toughness and the notch strength of Quasi Isotropic carbon fibre laminates. Patterns of laser-engraved micro-cuts were inserted in the micro-structure of the laminate to promote crack deflection and force the formation of large bundle pull-outs during crack propagation. The design of the patterns of microcuts was defined following the predictions of a newly developed Finite Fracture Mechanics criterion. The technique allowed to achieve a 20% increase in the laminate notched strength and an 190% increase in the laminate translaminar work of fracture when compared with the un-modified baseline material.
A semi-analytical Monte Carlo fibre bundle model was developed to investigate the role of dynamic... more A semi-analytical Monte Carlo fibre bundle model was developed to investigate the role of dynamic effects and fracture mechanics in the longitudinal tensile failure of fibre-reinforced composites. To the knowledge of the authors, it is the first time that both effects are implemented in a fibre bundle model through direct simulation. The formulation includes a field superposition method to calculate the stress concentration around broken fibres which captures the effect of clusters of broken fibres. The Monte Carlo process was optimized to allow the simulation of bundles with thousands of fibres. The comparison between the predicted bundle strengths and experimental data suggests that, although the dynamic stress concentration significantly decreases the bundle strength, the trend and magnitude of the size effects in large composite bundles can only be explained considering fracture mechanics as the failure mechanism.
Carefully-placed patterns of micro-cuts have been designed and then used to increase the translam... more Carefully-placed patterns of micro-cuts have been designed and then used to increase the translaminar work of fracture in thin-ply CFRP composite laminates. These patterns of micro-cuts are able to deviate a translaminar crack and force the formation of large bundle pull-outs. The technique led to a 68% increase in the laminate notched strength and a 460% increase in the laminate translaminar work of fracture when compared with the un-modied baseline material. Part of the improved performance was found to be due to the generated interaction of failure mechanisms between contiguous plies with dierent orientation; this process for generating interaction opens new possibilities for micro-structure design which will be explored in future works.
Uploads