Fibre reinforcement and stacking sequence influence on the through-thickness compression behaviour of polymer composites

A combined experimental and numerical study was performed to investigate the influence of multi-axial stress states and reinforcement type on the constitutive response of fibre reinforced epoxy polymers. The constitutive behaviour of unidirectional and cross-ply layups of carbon and glass fibre reinforced epoxy resin, IM7/8552 and S2/8552 respectively, was investigated. Prismatic short block specimens at different off-axis angles were tested under quasi-static through-thickness compression. The experiments were simulated with an enhanced non-linear material model based on shear localisation planes and pressure dependency, which represents the elastic and plastic experimental behaviour better than other formulations. The results show that the overall constitutive response is highly dependent on the fibre reinforcement type and multi-axial stress state on the mesoscale. In order to obtain an accurate description of the material behaviour, measurement aspects such as determining the correct orthotropic elastic constants, especially the Poisson's ratios, are highlighted. Furthermore, particular focus is also drawn on important modelling aspects such as material non-linearity and pressure effects.