Deformability in General Yielding Unstable Fracture of Weldments of Structural Steels

Abstract

The welded joint is prepared to have a certain value of deformability as well as load-carrying capacity. Appreciable deformation of the structural component will be realized in the general yielding stage. In order to evaluate welded joint properties from the standpoint of engineering assessment for selecting materials, it is important to consider the criterion and deformability in unstable general yielding fracture of welded joint with defects. In the present report, attention is paid to the COD-criterion as the onset of unstable fracture beyond general yield, and deformation behaviors in the vicinity of notch tip of notched plate are studied in taking account of COD-gloval applied strain e∞. (overall strain in sufficient large gauge length). It is made a clear that the COD-concept can be adopted as the engineering fracture criterion for onset of fracture beyond general yield in the range that plastic constraint factor is not larger than unity. According to non-linear fracture mechanics approach in homogeneous materials, COD is proportional to the overall strain, and the proportional constant N is a function of specimen geometry and strain hardening exponent, n. In wide plate, N-value is almost equal to 1 and 2 for low strength C-Mn steel and high strength steel such as HT 80, respectively. In welded joint, the deformation behaviors is affected by the mechanical heterogeneity, and the COD vs. overall strain relation is not linear and mainly depends on the strain hardening exponent ratio.