The compression-after-impact strength of woven and non-crimp fabric reinforced composites subjected to long-term water immersion ageing

摘要

The current work examines the durability of composites reinforced with glass fibre woven fabric as well as non-crimp fabrics (NCF) immersed in water at 43, 65 and 93 °C for up to 2.5 years. Low velocity normal impact has been induced at various time intervals before and after water immersion at energy levels of 2.5, 5 and 10 J. Following impact the plates were tested statically in compression to determine the residual strength for assessment of damage tolerance. The compression strength suffered significant reductions from the water absorption and the low velocity impact with values being dependent to the time of immersion and the water temperature. A parallel behaviour was monitored, in terms of strength reduction over time, of plates impacted prior to water immersion with the plates that contain no damage. For specimens where impact damage introduced after water immersion lower compression-after-impact (CAI) strength was observed at the same energy levels. An increase in damage diameter was evident, regardless the reinforcement type, though the gradually produced greater density of through thickness damage was responsible for the significant lower compression strength values. The presence of 0° fibres for the NCF composites as the main load bearing element dictated the sensitivity to impact as well as the corresponding residual strength. For composites with woven reinforcement, damage was contained and localized by the fabric weave and effective stress redistribution seemed to be the mechanism for the relatively higher residual strengths obtained. A semi-empirical model has been used with high accuracy in fitting the given experimental data and draw conclusions from the comparisons.