Observation of Blunting Process in J_Ic Tests

Abstract

J_Ic tests were performed on HT80, A533B, SM50A and SUS 304 steels, as per the JSME Standard Method of Test for Elastic-Plastic Fracture Toughness J_Ic. 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 SZW_c was influenced by the elongated microcracks. The J_Ic 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 SZW_c, gave almost the same J_Ic values determined by the JSME R-curve method.