Effect of cracked weld joint and yield strength dissimilarity on crack tip stress triaxiality

Abstract

This paper is concerned with an elasto-plastic analysis of a weld joint containing a central crack in the weld material (WM) whose yield strength may differ from that of the base material (BM). Stress triaxiality along the path of expected crack extension is found to be influenced not only by the applied tensile load level and crack length relative to the specimen width but also by the degree of BM/WM mismatch in the yield strength. Three different cases are analyzed by application of a two-dimensional finite element analysis. They are referred to as under-match, even-match and over-match which correspond, respectively, to the WM yield strength being less than, equal to and greater than that of the BM. In general, the stress triaxiality along the crack front tends to increase for an under-matched weld and decrease for an over-matched weld using the even-matched case as a reference. As the crack length is reduced for a given specimen width, the stress triaxiality decreases accordingly and the BM/WM material dissimilarity becomes more obvious. Displayed graphically are also the crack front plastic zone size that increases with the applied tensile load level and suffers a discontinuity across the weld line.