5 - Three-dimensional invariant-based failure criteria for transversely isotropic fibre-reinforced composites

Abstract

This chapter describes failure criteria for polymer composites reinforced by unidirectional fibres. The failure criteria are based on an invariant quadratic formulation based on structural tensors that accounts for the preferred directions of the transversely isotropic material. Failure in a single UD ply is predicted, requiring the analysis of strains and stresses ply-by-ply when analysing multidirectional laminates. Because the proposed failure criteria does not use geometrical information to predict failure (due to its invariant-based formulation), we propose a pragmatic approach to estimate the orientation of the fracture plane. To account for the effect of ply thickness when the laminae are embedded in a multidirectional laminate, the in situ properties are defined in the framework of the failure criterion for transverse damage mechanisms. When compared against experimental data available in the literature, good agreement for transverse failure modes, for failure under off-axis loading and for the effect of superposed hydrostatic pressure on failure behaviour of different fibre-reinforced composites is obtained. For more complex three-dimensional stress states, where the test data available shows large scatter or is not available at all, a computational micro-mechanics framework is used to validate the failure criteria. We obtain a good correlation between the predictions of the two modelling strategies.