Multi-scale polymeric composite design for ballistic impact protection

Abstract

Polymeric composites are being widely used in ballistic protection systems due to their excellent projectile capturing capabilities. One of the most promising materials is the Ultra-High-Molecular-Weight-Polyethylene (UHMWPE) fibre-reinforced composite which possesses high strength and low density. The aim of this PhD program is to build an accurate, physically sound, and computationally efficient constitutive model to predict the impact performance of UHMWPE composites. A multi-scale design approach was adopted from the macro-fibril level to a full-scale shield panel. The behaviour of UHMWPE fibres and thermoplastic polyurethane (TPU) resin was characterised and validated against experimental data with an emphasis given on the viscoelastic-plastic nature of the macro-fibril. UHMWPE laminates possess a high fibre volume fraction, typically exceeding 80%, and they are manufactured in a [0/90] ply configuration. A cross-ply Representative Volume Element (RVE) for the Dyneema HB26 composite was built based on macro-fibrils, to observe failure mechanisms associated with the fibre's substructure. Furthermore, images from dark field microscopy have revealed a variation in the cross-sectional shape of the fibre as well as a random fibre packing sequence through the thickness of each ply. In order to understand the effects of the microstructure morphology on the macro-scale mechanical response, both observations have been taken into account within the finite element RVE models. The micromechanical behaviour of the laminate was investigated under various strain-rates with special consideration given to the non-linear in-plane shear response. A three-dimensional (3D) continuum level constitutive model, that predicts the dynamic behaviour of UHMWPE composites, was developed based on the findings of the RVE numerical results and experimental observations. A full-scale polymeric shield model was used to predict the ballistic impact performance of the composite, for different target thicknesses and projectile materials. The stochastic variation of fibre strength was implemented to derive probability levels of the projectile residual velocity. The proposed modelling methodology was extended to other materials such as LCP and CFRP composites and hybrid systems constructed by these two. The model was validated against experimental data and was able to accurately predict the behaviour of polymeric and hybrid laminates under impact.