The influence of long term water immersion ageing on impact damage behaviour and residual compression strength of glass fibre reinforced polymer (GFRP)

Matrix and fibre/matrix interfacial degradation are end-effect characteristics of glass fibre composites subjected to water for very long periods. The performance of these materials to an external impact in a deteriorated condition and the associated residual strength are difficult to predict and usually accelerated tests are considered instead. This paper examines the durability of an isopthalic polyester resin reinforced with non-crimp glass fabrics in a hydrothermal environment (water baths at 65 °C) for up to 30 months.Water uptake measurements were conducted initially to investigate the degradation profiles of glass fibre composite plates after being permeated by water. Matrix dissolution and interfacial damage appeared on the specimens following prolonged immersion while the absorption behaviour was found typically non-Fickian. The weight of the composite plates initially increased due to water diffusion up to month 14 and thereafter decreased due to material losses. Impacting after the conditioning phase for various time intervals did not increase considerably the damage size but produced a greater density of through thickness damage, which resulted in a lower compression after impact (CAI) strength measured on a newly designed miniaturised CAI rig. The reductions in compression strength over time tent to reach a minimum plateau after extended exposure to water, irrespective of the applied impact energy, while the dominant mechanism causing failure seemed to be the prolonged immersion to water rather than the level of delamination, introduced by the applied impact loading.