Simulation of Fatigue Crack Growth in Weld Joint of Thin Structures Using Characteristic Tensor

Abstract

It is known that fatigue life of welded structures, such as automotive and ship structures, is greatly influenced by welding residual stress. In case of real structures, the orientation of the stresses produced by static load and that produced by repeated load and that of welding residual stress are generally different from each other and they form a highly complex multi axial stress states. On the other hand, the fatigue behaviour has been mostly studied for uniaxial stress state without residual stress. The crack growth rate is related to the stress intensity factor range ΔK such as in the Paris Low [1]. To predict the fatigue behaviour of real welded structures, the three dimensional stresses produced by static load, repeated load and welding must be rationally correlated with a scalar value ΔK. The author proposes a Characteristic Tensor which characterizes the singular stress field at crack tip and its invariant parameters, such as principal values or invariants which has similar form as strain energy density, are used to compute ΔK in a consistent manner. Its potential usefulness is demonstrated through simple examples.