Vibration platform modified

Abstract

In steel welds there is often a large variation in fracture toughness and mechanical properties between the weld metal, base material and the various heat affected zone (HAZ) microstructures. The stress field in front of a crack in a weldment can be noticeably affected by the strength mismatch between the weld metal, HAZ and the base material. The crack position relative to the various microstructures will clearly influence the strength mismatch effect. In this paper the influence of crack tip positioning on the fracture performance of strength mismatched steel welds has been studied both experimentally and by FEM analysis. For a mismatched weld with local brittle zones small changes in crack tip location can give considerable changes in the fracture performance of a CTOD specimen. A high degree of strength mismatch increases the effect of crack positioning. Weld metal overmatch increases the stress level in the heat affected zone due to material constraint and thereby reduces the cleavage fracture resistance of the weldment when the coarse grained HAZ (CGHAZ) controls the fracture. The detrimental effect of high overmatch is most pronounced for specimens with notch position at fusion line and a short distance into the brittle CGHAZ. The Weibull stress has been shown to be a suitable fracture parameter in the case where one microstructure clearly controls the cleavage fracture and the calculation of the Weibull stress therefore can be limited to this zone.