Modelling of Impact Damage in Composites

Abstract

The work presented in this thesis is a detailed study of impact damage subjected to tensile and compressive loading to determine the stiffness reduction of the damage region and identify the damage mechanisms and important parameters that control the severity of the stiffness reduction. Once the important damage parameters had been indentified a homogenised non-linear soft inclusion model was developed. This represents the mechanical and material behaviour of an impact damage region under tensile and compressive loading in a simple and easy to implement user material format. The influence of different damage parameters was determined by building ply level models of idealised impact damage with delaminations at every ply interface and fibre fracture cracks within the plies. Parametric studies were conducted on the shape and size of delaminations and on crack density and crack distribution under tensile and compressive loading and these models were validated against experimental results. In order to determine the influence of fractured fibres on the residual compressive stiffness the fibres were modelled at the micro scale with individual fibres embedded in an elastic-plastic matrix.