On Mode-I and Mode-Ii Interlaminar Crack Migration and R-curves in Carbon/epoxy Laminates with Hybrid Toughening Via Core-Shell Rubber Particles and Thermoplastic Micro-Fibre Veils

This study investigates the influence of hybrid toughening-via core-shell rubber (CSR) particles and non-woven thermoplastic veils-on the delamination resistance, crack migration and R-curve behaviour in carbon fibre/ epoxy laminates under mode-I and mode-II conditions. Core-shell rubber particles, varying in size from 100 nm to 3 mu m, with 0-10 wt% content, are dispersed within the epoxy resin, and thermoplastic micro-fibre veils with polyphenylene sulfide (PPS) fibres, with 5-20 g/m(2) areal weight, are introduced at the interlaminar region to achieve hybrid toughening. Carbon fibre/epoxy laminates are manufactured with a two-part resin using vacuum infusion and out-of-autoclave curing. Double cantilever beam (DCB) and four-point end-notch-flexure (4ENF) specimens are used to obtain mode-I and mode-II fracture energies and R-curves. Damage mechanisms and crack paths are characterised using fractography that provide understanding of energy dissipation. The results show that the hybrid toughening significantly improves fracture initiation and propagation energies (i.e. mode I initiation by similar to 245% and propagation by similar to 275%, and mode-II initiation by similar to 64% and propagation similar to 215%) by extrinsic and intrinsic toughening mechanisms. Moreover, it is shown that rising R-curves can be achieved with hybrid toughening when compared with falling R-curves obtained with just thermoplastic veil toughening. Fractography revealed that the hybrid toughening constrained the crack predominantly within the veil region, making it harder to grow and absorb more energy.