Summary
Double-cantilever beam (DCB) specimens are widely used to measure the mode I critical-energy release rate GIc of glass-fiber reinforced polyester composites (GF/PO composites). It showed GIc varied significantly during crack propagation. GIc of GF/PO composites are higher than that of the pure polyester (PP) resin because of the additional force required to fracture fiber bridging in GF/PO composites. Comparative DCB tests were carried out to demonstrate the occurrence of fiber bridging. GIc varied markedly and were much dispersed, which would induce little variation when initial crack length was 40 mm. The fracture characteristics were analyzed by scanning electron microscope.