Rate effects in the fracture of glass fibre chopped strand mat composites

The effect of varying loading rate on the fracture properties of composites based on glass fibre chopped strand mats and epoxy-based vinyl ester resins has been studied. Initially, the fracture behaviour of the pure resins was studied by using simple flexure and fracture mechanics test techniques. Following this, a series of perforation tests was undertaken on small plate-like samples in order to assess the rate sensitivity of the perforation threshold and to determine if this value could be related to the fracture properties of the composite. It was found that the work of fracture, Wi, increased with increasing loading rate over the wide range of conditions examined. It is believed that this increase is related to the rate-dependent fracture properties of the glass fibres. Increasing the loading rate results in an increase in fibre 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 the plate impact data, with the threshold increasing rapidly with loading rate. It was found that the work of fracture determined on single-edge-notch bend samples correlated well with the drop-weight impact perforation data. (C) 1997 Elsevier Science Limited.