Effects of Fracture Controlling Factors on Cleavage Fracture Initiation in Specimens with Heterogeneity along Crack Front

Abstract

Fracture toughness tests of specimens with mechanical and metallurgical heterogeneity along crack front have been carried out.
The main attention of the present study is paid to effects of fracture controlling factors such as fraction and location of embrittlement region in crack front on fracture toughness, in particular at cleavage crack initiation. Using specimens extracted from stainless clad steel and welded joint of HT80 steel, 3-point bending tests are conducted.
The deformation processes of specimens before fracture initiations are affected by neither mechanical nor metallurgical heterogeneity along crack front, and subsequent cleavage fractures initiate only in HT80 region regardless of its fraction and location in crack front. Cleavage resistances of specimens with heterogeneity along crack front are roughly equal to those of HT80 steel specimens. In the case that HT80 region is away from the center of thickness and exists only in vicinity of specimen surface, however, cleavage resistance of specimen is observed as apparently higher value than any other cases.
According to these results, fracture toughness values of specimens with heterogeneity along crack front in particular reference to cleavage crack initiation are evaluated as roughly equal to those of specimens filled with the lower-toughness material in crack front.