Abstracts Category : Other

Impact damage behaviour of lightweight materials

by Kedar Sanjay Pandya

Impact damage resistance is an essential requirement of lightweight structural components for high-performance applications. The aim of this thesis is to study the impact damage and perforation behaviour of lightweight materials including thin aluminium alloy plates and carbon fibre reinforced epoxy composites. The focus of this investigation is on the stress state and strain rate dependence of failure, and the effect of microstructural modifications on indentation and impact response.The thesis is divided into three parts. In the first part (Chapter 2) the impact response of thin monolithic ductile aluminium alloy plates is investigated. Impact perforation experiments are performed using different projectile nose shapes to span a wide range of stress states at the onset of ductile fracture. Impact perforation behaviour, ballistic limit velocity, energy absorption capability and sensitivity to projectile tip geometry are evaluated. Modes of deformation and failure during impact are assessed experimentally. It is shown that modelling the stress state and strain rate dependence of plasticity and failure is crucial to accurately predict ductile fracture initiation in thin metal plates.In the second part (Chapters 3 and 4), the stress state and strain rate dependent yield and failure behaviour of epoxy resin is investigated. An iterative numerical-experimental approach is shown to be essential to develop a material model capable of predicting the failure behaviour of epoxy for a wide range of stress triaxialities across different regimes of failure. The influence of microstructural modifications in epoxy, through two different toughening strategies, on its failure behaviour is investigated. The effect of increasing the applied strain rate on the stress state dependent response of epoxy is investigated to provide an insight into the impact damage resistance of carbon fibre reinforced epoxy composites.In the third part (Chapter 5), experimental studies are conducted on the quasi-static indentation and impact perforation response of plain weave carbon fibre reinforced epoxy composites to investigate the effect of toughening the epoxy matrix to improve resistance to indentation and impact. The nose shape sensitivity of failure initiation in carbon/epoxy composite targets is assessed by considering indenters with different tip geometries.Conclusions and suggestions for future work are presented in Chapter 6.