The influence of thermohumidity on compression after-impact properties of fibre reinforced epoxy laminates

Advanced composite materials, particularly in aerospace components, are expected to survive in a range of temperatures and humid environments in different parts of the world. In addition they can expect to sustain low velocity impacts during operation. The aim of the work reported in this paper was to quantify the influence of thermohumid. conditions on compression after impact properties of glass, carbon and hybrid fibre reinforced laminates. The extent of delamination and other damage, resulting from low velocity impact of dry materials, was measured using ultrasonic C-scan and optical sectioning techniques. The effects of subsequent exposure to thermohumid conditions of 60degreesC and 95% relative humidity was investigated for periods up to eighty days. Glass reinforced laminates exhibited less delamination damage than carbon laminates base on the same epoxy matrix, and therefore perhaps not surprisingly the carbon laminates absorbed a higher percentage of moisture. In the carbon laminates the water attacked the fibre/matrix interface with a resulting decrease in interlaminar shear strength, where at the same levels of moisture uptake, the glass fibre laminates were little affected. The glass transition temperature of the polymer matrix was shown to vary in a linear way with the percentage moisture uptake for all laminates, and matrix dominated properties were most greatly influenced. The results demonstrate that moisture up-take was less significant than energy of impact or fibre type. A model of the influence of impact energy on compression after impact degredation ratio is presented.