Shear driven deformation and damage mechanisms in high-performance carbon fibre-reinforced thermoplastic and toughened thermoset composites subjected to high strain loading

High strain loading response of high-performance aerospace grade polyether-ether-ketone (PEEK) and toughened epoxy carbon fibre-reinforced composites has been investigated in pre-impregnated laminates having identical carbon fibre volume fraction, i.e. nearly 65%. Tensile cyclic loading tests have been carried out on the laminates with [±45°]8S stacking sequence, in order to characterise inelastic (plasticity) parameters for the two laminates progressively up to high strains (up to 11% strains), in correlation with the fibre and matrix micro-scale deformation and damage characteristics. The most suitable processes to achieve ultimate mechanical performance were used for manufacturing of the laminates. It has been observed that the PEEK composite exhibits higher mechanical performance at high strains under cyclic loads compared to epoxy composites (150% ultimate failure strain, 380% strain hardening and 200% ultimate failure stress) due to having superior micro-scale shear deformation in PEEK attributed to. interfacial strength of fibre-matrix prior to the ultimate failure, as opposed to extensive micro-cracking, coalescence and fibre-matrix debonding in the epoxy composite