Abstract
Welded joints, especially electron beam welded joints have significant heterogeneity of mechanical properties. Fracture mechanics parameters, for example J and COD, have been applied for homogeneous materials. The applicability of these parameters to heterogeneous welded joints has not yet been made clear. In the present study, fracture toughness tests were carried out on HT80 steel EB welded joints and the process of ductile crack initiation was observed in detail. Elastic-plastic FEM analysis of the welded joints was also carried out.
In the HAZ-type specimen, a large crack tip opening displacement was observed in the base metal region, the strength level of which was lower than that of the weld metal. The main reason for the low JIc-value of the HAZ specimen seemed to be that plastic deformation concentrates in the base metal region due to the heterogeneity of strength. The path-independency of the J-integral holds approximately for heterogeneous welded joints in the range of the yield stress ratio of the base metal and the weld metal up to 1.74. It may be possible, therefore, to evaluate the fracture toughness by using the J-integral even in the case of heterogeneous welded joints.
