Strain rate dependent deformation and damage behaviour of textile-reinforced thermoplastic composites

The present work focuses on the detailed characterisation and modelling of the strain rate dependent deformation and damage behaviour of a continuous fibre-reinforced thermoplastic composite (TPC) with multi-layered flat bed weft-knitted reinforcement. For this purpose, a novel experimental testing procedure is developed in the first part of this work. A so-called stepwise loading and reloading with stress relaxation and strain retardation phases enables the determination of the elastic, inelastic and viscoelastic portions with only one experimental test. Additionally, microscopic diagnostic is employed to investigate the complex deformation and damage behaviour and its provoking phenomenological damage mechanism like inter fibre failure and inelastic deformation. After the detailed experimental characterisation, an adapted viscoelastic-plastic damage model is developed in the second part of this work. This model on lamina level is based on a modified damage-plasticity model proposed by LADEVÃZE and uses an additional spring-dashpot system for describing the viscoelastic overstress. This model is implemented as a user-defined material (VUMAT) in the FE program ABAQUS for realising a model validation and structure application