On the Estimation of Fatigue Crack Growth Rate at Welding Residual Stresses Fields

Abstract

The present paper is one of researches which are carrying out to clarify the effect of local constraint in the weld zone on fatigue crack growth rates in welded joints. This local constraint may be produced by welding residual stresses, the microstructure and the mechanical properties. In particular, the effect of welding residual stresses on the behavior of which the fatigue crack propagates perpendicularly through the weld bead has quantitatively been investigated by means of fracture mechanics and fractography in association with the crack length to residual stresses field and the stress ratio.
The fatigue crack growth rates in welded joints were markedly influenced by welding residual stresses. Namely, the growth rates of which the crack propagated perpendicularly through the weld bead decreased drastically by the compressive residual stresses at some stress intensity level and increased again with increasing stress intensity beyond the minimum value of crack growth rate. This minimum value depended on the initial welding residual stresses, the crack length to residual stresses field and the stress ratio. Therefore, it became clear that the fatigue crack propagation behavior into welding residual stresses fields is well explained by the effective stress intensity factor to define from both the welding residual stresses- and the plastic-induced crack closure.