An interpolation method is proposed in this paper to estimate the distribution of the transverse welding residual stress in the plate thickness direction as well as the redistribution of the residual stress as crack penetrates the plate thickness. The distribution of the residual stress was interpolated by a truncated Fourier Series function and the redistribution of the residual stress was estimated through a series of such functions. Results indicate that once a fatigue crack developes in a positive or negative residual stress domain the crack tip remains in the same domain irrespective of the original residual stress pattern.
The fatigue strength of welded tubular joints suffers generally and partly because of the residual stresses induced by the welding process. In recent fatigue tests carried out on such joints[l j, it was found that the welding residual stresses have a significant detrimental effect on fatigue strength as shown in Table 1. In one of the, cases the as welded joint failed after 2.55 million cycles while the stress relieved joint showed no sign of crack initiation at all at 20 million cycles with the same applied hot spot strain. It was after the hot spot strain was doubled that the stress relieved joint was tested to failure. In both cases and in general, surface cracks initiated near the weld fusion line at the highest stress concentration factors and propagated, while penetrating the plate thickness, along the curved weld line. In order to understand how the residual stresses influence the fatigue strength, the knowledge of the distribution of the residual stress in the as welded condition and the redistribution during crack initiation and propagation is essential. The major concern for welded tubular joints is the transverse welding residual stress and its distribution in the plate thickness direction.
