Rate dependent non-linear mechanical behaviour of continuous fibre-reinforced thermoplastic composites – Experimental characterisation and viscoelastic-plastic damage modelling

Abstract

The presented work contains both a detailed rate dependent experimental characterisation and the development of a viscoelastic-plastic damage model for the mechanical behaviour of continuous fibre-reinforced thermoplastic composites (TPC). A novel experimental procedure, so-called stepwise loading-unloading test with relaxation and retardation periods, is employed to analyse the non-linear deformation and damage behaviour of TPC materials. This testing procedure enables the determination of the elastic, inelastic and viscoelastic portions with only one experimental test. To investigate the complex mechanical behaviour and its provoking phenomenological damage and deformation mechanisms on the microscale, additional experimental diagnostic methods are employed. Based on the experimental results for a continuous glass fibre-reinforced polypropylene (GF/PP) composite with non-crimped reinforcement, a viscoelastic-plastic damage model is developed to describe the complex mechanical behaviour. Therefore, a damage-plasticity model is improved by using additional spring-dashpot systems for the calculation of the viscoelastic overstresses. This mesoscopic model describes the behaviour of single plies of a TPC laminate. After the implementation as a user-defined material subroutine into Matlab and Abaqus (Vumat), the model parameter identification and validation is performed as well as the structural behaviour is predicted.