Establishment of unified fatigue design maps for different types of fracture mode of single-sided fillet welded T-joints

Abstract

Pure bending fatigue tests were conducted with single-sided fillet welded T-joint specimens. Two load conditions, which were given the tensile and compressive stresses in the weld toe, were applied, and fatigue strengths at 2×10⁶ cycles were determined. Next, we conducted crack analyses simulating the fatigue tests by FEM. In the analyses, initial toe crack of 0.2 mm and root gap were modeled by slit, and opening displacements of the slit tip were calculated. From these displacements, stress intensity factors acting on the maximum principal stress plane were calculated. By comparing fatigue tests and crack analyses, fracture criteria for pure bending were estimated. These criteria were extended to the conditions in which tension and bending load were applied simultaneously, and fracture limit lines based on hot spot stress were calculated in each root gap and weld toe. By using these limit lines and material based strength, the fracture design maps that can be evaluated the fatigue strength of both root gap and weld toe at the same time are proposed.