Effect of plastic deformation on fatigue crack behavior in weld residual stress field

Crack closure behavior in fatigue crack propagation process is induced by plastic deformation near crack. In the present paper, the effect of plastic deformation on fatigue crack closure in low strength material and its welded joint was studied. The results obtained are as follows. Crack closure was caused by plastic deformation near crack surface. Generally, the crack opening ratio in high yield strength material was higher than that in low yield one. This tendency results from a low degree of deformation near crack surface. In addition, in welded joint, the crack propagation rate was higher than the mother metal, though the crack opening ratio was almost 1 by the effect of residual stress. This was explained by the effect of restraint for plastic deformation, which was induced by the existence of compressive stress field ahead of crack.