Carwyn Ward - Academia.edu (original) (raw)
Papers by Carwyn Ward
Journal of Manufacturing and Materials Processing
Non-destructive testing (NDT) is a quality control measure designed to ensure the safety of produ... more Non-destructive testing (NDT) is a quality control measure designed to ensure the safety of products according to established variability thresholds. With the development of advanced technologies and a lack of formalised knowledge of the state-of-the-art, the National Composites Centre, Bristol, has identified that the increasing complexity of composite products will lead to some severe inspection challenges. To address the apparent knowledge gap and understand system complexity, a formulaic approach to introduce intelligence and improve the robustness of NDT operations is presented. The systemic development of a high-fidelity knowledge base (KB) involves the establishment of a capability matrix that maps material, component, and defect configuration to the capabilities and limitations of selected detection methods. Population and validation are demonstrated through the experimental testing of reference standards and evaluated against an assessment criteria. System complexity in ult...
American Society for Composites 2017
Composite manufacturing uses pressure and temperature in lay-up to produce parts with high volume... more Composite manufacturing uses pressure and temperature in lay-up to produce parts with high volume fractions, limited features, and low porosity. Modern prepregs are very complex, incorporating significant levels of thermoplastic toughener that makes them behave dually: as unconsolidated thermoplastics at low temperatures, and conventional thermoset prepregs at elevated temperatures. This paper presents an experimental programme to study the compressibility of a modern prepreg at various temperatures and constraint conditions using a Dynamic Mechanical Analyser. Testing revealed a number of physical phenomena, including gradual transition from shear squeezing flow to bleeding percolation flow, strong constraining effects of adjacent non-cured plies, and non-monotonic compressibility over the temperature range of 20-90°C.
This paper presents a process improvement framework built on previous research activities at the ... more This paper presents a process improvement framework built on previous research activities at the University of Bristol. The work focusses on hand lay-up and seeks to reduce variability, improve productivity and increase manufacturability of future designs. The framework is based on a double-loop learning model which incorporates prediction, capture and feedback. The predictive method employed uses a kinematic drape model as part of an expert system. The expert is needed to translate the model outputs into a more realistic set of drape instructions. The lay-up is captured by video analysis and quality data captured using an on-line tool. This data is then fed back to the user to facilitate decision making.
The curing behaviour of a novel composite matrix formulation based on bisphenol A epoxy resin, an... more The curing behaviour of a novel composite matrix formulation based on bisphenol A epoxy resin, an anhydride curing agent, and a tertiary amine accelerator is investigated. The curing kinetics are studied using both isothermal and dynamic differential scanning calorimetry (DSC) experiments. The cure kinetics of the thermoset resin are best described by a modified autocatalytic model, where good agreement between experimental and predicted model results is obtained during the initial stages of the cure reaction.
Fused Deposition Modelling (FDM), a form of additive manufacture, is typically constrained to 2.5... more Fused Deposition Modelling (FDM), a form of additive manufacture, is typically constrained to 2.5D, vertically stacked layers; curved layers have been shown to possess improved mechanical properties and surface finish but require complex toolpath generation. This paper demonstrates methods of generating thin-walled FDM components with curved layers suited for use within aerospace composite sandwich panels; secondary structures containing high complexity and low production volumes ripe for manufacture using additive techniques. An industrial robot arm and a PC-based open-source controller allowed for significantly higher degrees of toolpath complexity for FDM than realised using conventional systems. Three use cases are presented to describe the manufacture of FDM components, with the first demonstrating deposition on a rotating cylinder, allowing for customised stiffening and reinforcement. The second shows a curved surface defined by an STL file, with the nozzle orientated to remai...
Hitachi Chemical Company Ltd. (HCCL) has developed a glass fibre reinforced polymer composite bas... more Hitachi Chemical Company Ltd. (HCCL) has developed a glass fibre reinforced polymer composite based on an anhydride-cured epoxy resin. Preliminary HCCL testing has suggested that it has improved interlaminar and mechanical properties compared to the amine-cured epoxy system which is currently used, making it an attractive alternative for use in wind turbine blades. In this work, extensive studies on the epoxy-anhydride system were conducted, allowing the determination of thermal properties, such as the glass transition temperature and modulus, along with cure kinetics. Processing parameters of rheological behaviour and in-situ resin shrinkage during cure were also studied. The apparent interlaminar shear strength was determined to be 62 MPa, verifying the improved interlaminar properties originally stated. The multifaceted nature of this research enabled the characterisation of a novel composite system, this will be pivotal in future research to develop an informed manufacturing pro...
A novel test method has been developed to test the contribution of the tuft drift mechanism obser... more A novel test method has been developed to test the contribution of the tuft drift mechanism observed in tufted sandwich structures under crushing loads. A test fixture has been produced capable of replicating the mechanism for a range of tuft configurations. Tests were carried out, looking at the number, alignment and spacing of tufts within the foam, and their effects on the load and energy absorption of the material. Results of the tests showed single tufts behaving in a consistent manner, but multiple tuft configurations were harder to control. An increased load, and hence energy absorption was observed with increasing numbers of tufts, however this effect diminished if interactions between the tufts did not take place. Future work would look to improve the test method, and ensure that the alignment of tufts could be better controlled to ensure a more accurate representation of failure mechanisms observed in larger test panels.
Tufted sandwich panels have been shown to be effective energy absorbing structures when subjected... more Tufted sandwich panels have been shown to be effective energy absorbing structures when subjected to in-plane compressive loads, such as those exhibited during an automotive vehicle side impact. However, up to now, no focus has been paid to understanding the complex failure mechanisms that take place during this type of loading, in particular what happens to the individual tufts, both during and after failure. In this study, an experimental test procedure was used to observe the behaviour of tufts during edgewise crushing. Overall, the tufted samples showcased a prolonged and more stable failure than the untufted baseline. The test also showed a clear drifting and stacking motion of the tufts, as well as highlighting a number of secondary failure mechanisms that take place, that have not been documented before. Further understanding of how these occur could lead to better performance and controllability of the global failure of such a structure.
Journal of Advanced Materials, 2016
A new two-stage method for the automated manufacture of high performance composites components is... more A new two-stage method for the automated manufacture of high performance composites components is presented which aims to combine the capacity for forming complex shapes of Hand Layup with the speed of existing automated systems. In the first stage of the new process plies are formed into the approximate shape of the mould using a press mechanism. They are then passed onto a layup stage which uses multiple end effectors controlled by a six axis robot to stick the plies down onto the mould. This is the first time an automated process has been capable of forming sheets of woven prepreg onto truly complex moulds while maintaining a high level of fibre alignment. This work represents a condensed version of the second half of the thesis by the author entitled ‘The evolution and automation of sheet prepreg layup’.
In this work the application of fibre reinforced plastic (FRP) sandwich structures, with particul... more In this work the application of fibre reinforced plastic (FRP) sandwich structures, with particular focus on aramid fibre tufted sandwiches is being studied for automotive crashworthiness applications using impact testing and numerical simulation.
Journal of Manufacturing and Materials Processing
Non-destructive testing (NDT) is a quality control measure designed to ensure the safety of produ... more Non-destructive testing (NDT) is a quality control measure designed to ensure the safety of products according to established variability thresholds. With the development of advanced technologies and a lack of formalised knowledge of the state-of-the-art, the National Composites Centre, Bristol, has identified that the increasing complexity of composite products will lead to some severe inspection challenges. To address the apparent knowledge gap and understand system complexity, a formulaic approach to introduce intelligence and improve the robustness of NDT operations is presented. The systemic development of a high-fidelity knowledge base (KB) involves the establishment of a capability matrix that maps material, component, and defect configuration to the capabilities and limitations of selected detection methods. Population and validation are demonstrated through the experimental testing of reference standards and evaluated against an assessment criteria. System complexity in ult...
American Society for Composites 2017
Composite manufacturing uses pressure and temperature in lay-up to produce parts with high volume... more Composite manufacturing uses pressure and temperature in lay-up to produce parts with high volume fractions, limited features, and low porosity. Modern prepregs are very complex, incorporating significant levels of thermoplastic toughener that makes them behave dually: as unconsolidated thermoplastics at low temperatures, and conventional thermoset prepregs at elevated temperatures. This paper presents an experimental programme to study the compressibility of a modern prepreg at various temperatures and constraint conditions using a Dynamic Mechanical Analyser. Testing revealed a number of physical phenomena, including gradual transition from shear squeezing flow to bleeding percolation flow, strong constraining effects of adjacent non-cured plies, and non-monotonic compressibility over the temperature range of 20-90°C.
This paper presents a process improvement framework built on previous research activities at the ... more This paper presents a process improvement framework built on previous research activities at the University of Bristol. The work focusses on hand lay-up and seeks to reduce variability, improve productivity and increase manufacturability of future designs. The framework is based on a double-loop learning model which incorporates prediction, capture and feedback. The predictive method employed uses a kinematic drape model as part of an expert system. The expert is needed to translate the model outputs into a more realistic set of drape instructions. The lay-up is captured by video analysis and quality data captured using an on-line tool. This data is then fed back to the user to facilitate decision making.
The curing behaviour of a novel composite matrix formulation based on bisphenol A epoxy resin, an... more The curing behaviour of a novel composite matrix formulation based on bisphenol A epoxy resin, an anhydride curing agent, and a tertiary amine accelerator is investigated. The curing kinetics are studied using both isothermal and dynamic differential scanning calorimetry (DSC) experiments. The cure kinetics of the thermoset resin are best described by a modified autocatalytic model, where good agreement between experimental and predicted model results is obtained during the initial stages of the cure reaction.
Fused Deposition Modelling (FDM), a form of additive manufacture, is typically constrained to 2.5... more Fused Deposition Modelling (FDM), a form of additive manufacture, is typically constrained to 2.5D, vertically stacked layers; curved layers have been shown to possess improved mechanical properties and surface finish but require complex toolpath generation. This paper demonstrates methods of generating thin-walled FDM components with curved layers suited for use within aerospace composite sandwich panels; secondary structures containing high complexity and low production volumes ripe for manufacture using additive techniques. An industrial robot arm and a PC-based open-source controller allowed for significantly higher degrees of toolpath complexity for FDM than realised using conventional systems. Three use cases are presented to describe the manufacture of FDM components, with the first demonstrating deposition on a rotating cylinder, allowing for customised stiffening and reinforcement. The second shows a curved surface defined by an STL file, with the nozzle orientated to remai...
Hitachi Chemical Company Ltd. (HCCL) has developed a glass fibre reinforced polymer composite bas... more Hitachi Chemical Company Ltd. (HCCL) has developed a glass fibre reinforced polymer composite based on an anhydride-cured epoxy resin. Preliminary HCCL testing has suggested that it has improved interlaminar and mechanical properties compared to the amine-cured epoxy system which is currently used, making it an attractive alternative for use in wind turbine blades. In this work, extensive studies on the epoxy-anhydride system were conducted, allowing the determination of thermal properties, such as the glass transition temperature and modulus, along with cure kinetics. Processing parameters of rheological behaviour and in-situ resin shrinkage during cure were also studied. The apparent interlaminar shear strength was determined to be 62 MPa, verifying the improved interlaminar properties originally stated. The multifaceted nature of this research enabled the characterisation of a novel composite system, this will be pivotal in future research to develop an informed manufacturing pro...
A novel test method has been developed to test the contribution of the tuft drift mechanism obser... more A novel test method has been developed to test the contribution of the tuft drift mechanism observed in tufted sandwich structures under crushing loads. A test fixture has been produced capable of replicating the mechanism for a range of tuft configurations. Tests were carried out, looking at the number, alignment and spacing of tufts within the foam, and their effects on the load and energy absorption of the material. Results of the tests showed single tufts behaving in a consistent manner, but multiple tuft configurations were harder to control. An increased load, and hence energy absorption was observed with increasing numbers of tufts, however this effect diminished if interactions between the tufts did not take place. Future work would look to improve the test method, and ensure that the alignment of tufts could be better controlled to ensure a more accurate representation of failure mechanisms observed in larger test panels.
Tufted sandwich panels have been shown to be effective energy absorbing structures when subjected... more Tufted sandwich panels have been shown to be effective energy absorbing structures when subjected to in-plane compressive loads, such as those exhibited during an automotive vehicle side impact. However, up to now, no focus has been paid to understanding the complex failure mechanisms that take place during this type of loading, in particular what happens to the individual tufts, both during and after failure. In this study, an experimental test procedure was used to observe the behaviour of tufts during edgewise crushing. Overall, the tufted samples showcased a prolonged and more stable failure than the untufted baseline. The test also showed a clear drifting and stacking motion of the tufts, as well as highlighting a number of secondary failure mechanisms that take place, that have not been documented before. Further understanding of how these occur could lead to better performance and controllability of the global failure of such a structure.
Journal of Advanced Materials, 2016
A new two-stage method for the automated manufacture of high performance composites components is... more A new two-stage method for the automated manufacture of high performance composites components is presented which aims to combine the capacity for forming complex shapes of Hand Layup with the speed of existing automated systems. In the first stage of the new process plies are formed into the approximate shape of the mould using a press mechanism. They are then passed onto a layup stage which uses multiple end effectors controlled by a six axis robot to stick the plies down onto the mould. This is the first time an automated process has been capable of forming sheets of woven prepreg onto truly complex moulds while maintaining a high level of fibre alignment. This work represents a condensed version of the second half of the thesis by the author entitled ‘The evolution and automation of sheet prepreg layup’.
In this work the application of fibre reinforced plastic (FRP) sandwich structures, with particul... more In this work the application of fibre reinforced plastic (FRP) sandwich structures, with particular focus on aramid fibre tufted sandwiches is being studied for automotive crashworthiness applications using impact testing and numerical simulation.