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

Abstract

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 μm, 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 ∼245% and propagation by ∼275%, and mode-II initiation by ∼64% and propagation ∼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.