Fatigue crack growth of arbitrary planar cracks in welded components

Abstract

Engineering components that are subjected to cyclic loads frequently contain imperfections which can rationally be assessed using linear elastic fracture mechanics. Fatigue crack growth models make use of the stress intensity factor (SIF) range and the maximum SIF or R-ratio to describe the driving force for crack propagation. Determining the stress intensity factor in welded components is difficult because the stress field is complex due to the structural geometry of the component, the local geometry of the weld and the residual stresses caused by the welding process. In many cases, the crack geometry will also be complex. Weight function (WF) solutions for numerous crack geometries have been published, e.g. for through cracks, edge cracks, surface cracks and corner cracks. However, the use of the WF for cracks of arbitrary shape is less developed. The point-load WF method for arbitrary planar cracks gives sufficiently accurate estimates of stress intensity factors for embedded cracks, but the results for the surface and edge cracks are less accurate. A new form of the general point-load WF more suitable for surface breaking cracks is proposed and is combined with a crack tip plasticity-based crack growth model. During numerical simulations, cracks are normally modelled using a discrete number of linear segments. A new method for shifting these segments as a crack advances is also proposed. The method is verified based on comparison with published experimental results for welded rectangular hollow section joint subjected to bending and torsion.