RATE EFFECTS IN THE FRACTURE OF GLASS-FIBER CHOPPED STRAND MAT COMPOSITES

The effect of varying loading rate on the fracture properties of compo sites based on glass fibre chopped strand mats and epoxy-based vinyl e ster resins has been studied. Initially, the fracture behaviour of the pure resins was studied by using simple flexure and fracture mechanic s test techniques. Following this, a series of perforation tests was u ndertaken on small plate-like samples in order to assess the rate sens itivity of the perforation threshold and to determine if this value co uld be related to the fracture properties of the composite. It was fou nd that the work of fracture, Wi, increased with increasing loading ra te over the wide range of conditions examined. It is believed that thi s increase is related to the rate-dependent fracture properties of the glass fibres. Increasing the loading rate results in an increase in f ibre failure stress and, as a result, the stored elastic energy. This in turn results in increased crack bifurcation and the formation of a larger damage zone during fracture. Similar trends were observed in th e plate impact data, with the threshold increasing rapidly with loadin g rate. It was found that the work of fracture determined on single-ed ge-notch bend samples correlated well with the drop-weight impact perf oration data. (C) 1997 Elsevier Science Limited.