The effect of water immersion ageing on low-velocity impact behaviour of woven aramid–glass fibre/epoxy composites

Two different woven glass–aramid-fibre/epoxy laminates were subjected to water immersion ageing followed by instrumented low velocity impact testing. The hybrid aramid–glass reinforcement consisted of 10 plies of woven aramid–glass-fibre fabric or alternatively aramid-fibre fabric with glass-fibre fabric interlayers. The impacted plates were retested statically in compression to determine residual strength for assessment of damage tolerance. The maximum water absorption (4.1–4.4%) and water diffusion coefficients were found to be only slightly dependent on reinforcement configuration. The delamination threshold load and impact energy absorption were not significantly affected by the absorbed water. Due to low fibre–matrix adhesion, the prevailing failure modes at low impact energy were fibre/matrix debonding and interfacial cracking. The compression strength suffered significant reductions with water absorbed (28%) and impact (maximum 42%). The least sensitive to impact damage were wet samples of interlaminated composite. The experimental results of residual compression strength have been compared with predictions based on a simple, empirical model.