抄録
JIc tests were performed on HT80, A533B, SM50A and SUS 304 steels, as per the JSME Standard Method of Test for Elastic-Plastic Fracture Toughness JIc. The fracture processes of toughness specimens were also observed in detail.
Microcracks nucleated in the blunting region at almost the same time as the initiation of a stable ductile crack and were elongated with increasing deformation. It was found that the critical stretched zone width SZWc was influenced by the elongated microcracks. The JIc values determined by the JSME SZW method tended to be higher than those by the JSME R-curve method. The modified SZW method, using SZW0 which is given by subtracting the microcrack region width from SZWc, gave almost the same JIc values determined by the JSME R-curve method.
