Effect of Residual Stress on Fatigue Crack Growth Behavior of STS 42 Steel Weldments

Abstract

The fatigue crack growth behavior in butt-welded joints of STS42 steel was examined using compact type (CT), center-cracked tension (CCT) and single edge cracked (SEC) specimens, and the effects of specimen configuration, thickness, crack orientation and location of weld line in the specimens on the fatigue crack growth rate in the welded joints were examined in connection with welding residual stress.The fatigue crack growth rate in the CCT specimen was similar to or slightly higher than that in the base metal, whereas the crack growth rate in the CT or SEC specimen decreased considerably as compared with that in the CCT specimen, except for the CT specimen with a notch on the weld line. The crack growth rate increased slightly with increasing specimen thickness, regardless of specimen configuration. In the case of the CT specimen with perpendicular crack orientation with respect to the weld line, the crack lengths of the both sides of the specimen surface were often different each other. The side with an advanced crack front corresponded to the backing side with finishing pass. When a crack existed within the region of initial compressive residual stress field, the overall distribution of residual stress did not change appreciably. The effect of welding residual stress on the crack growth rate was the same as that of stress ratio on the growth rate of the base metal. The crack growth rate in the welded joints was correlated with the effective stress intensity factor range, ΔKeffR, which was estimated by superposition of the respective stress intensity factors for the residual stress field and for the applied stress, regardless of specimen configuration and distribution of residual stress in the specimens.