Fracture Behaviors of Fracture Toughness Testing Specimen with Heterogeneity Along Crack Front

Abstract

Fracture toughness tests of specimens with mechanical and metallurgical heterogeneity along crack front have been conducted. Using specimens cut from stainless clad steel (high tensile strength of 80 kg/mm2 strength level with SUS 304 stainless steel), both the conventional V-notch Charpy test and the bending COD test are performed to investigate the effect of the heterogeneity on the process of fracture and the fracture toughness controlling parameters.Absorbed energy of clad specimen in V-notch Charpy test is affected by various complicate factors such as fractions of brittle regime, energy for initiation of crack in the vicinity of notch tip, and energy for propagation of crack. In the heterogeneous material, absorbed energy in Charpy test may not be a proper fracture toughness parameter. The processes of fracture of static bending notched specimens are as follows : At low temperature, cleavage type fracture firstly initiates only in HT 80 steel region, and at high temperature, ductile fracture firstly initiates in SUS 304 steel region. In the case of fracture toughness testing of heterogeneity materials, it seems that stretched zone width can be a proper parameter of fracture toughness in particular relation to crack initiation. Fracture toughness values when original crack initiates in the some parts along crack front are roughly equal to those of specimens filled with the lower-toughness materials in crack front.