Effects of mechanical stress‐relieving on deformation fields near cracks in weldments

Abstract

Considerable papers which experimentally examined the effect of residual stress on the brittle fracture strength of weldment have been published. The effect of stress-relieving on the brittle fracture strength has been experimentally examined too. In those papers, the residual stress distributions were measured by the stress-relaxation method, assumed as a simple curve and represented by a simple function. There have been, however, few analytical works concerned with stress and strain near a crack in the residual weld stress field.In the present study, an as-welded plate and a welded plate stress-relieved mechanically are dealt with. Each of them has a through-thickness center crack perpendicular to the welding bead. The crack initiates after welding or after stress-relieving. The residual stresses due to welding and those after stress-relieving by the uniform pre-straining are measured by means of the ultrasonic technique, because, from a practical point of view, the residual stress should be measured nondestructively. A uniform tensile load perpendicular to the crack is applied to the plate. Stress, strain, plastic zone near a crack and crack opening displacement are examined by elasto-plastic finite element analysis as well as experiment. Considering the residual stresses distributed after pre-cracking, the deformation near the tip of a crack in a plane stress field are analyzed. The effect of residual stresses and that of stress-relieving on the deformation near a crack are revealed. The tensile residual stress around a crack tip contributes to the increase of stress, strain, plastic zone size near the crack and crack opening displacement. The stress-relieving contributes to the increase of fracture strength of welded plate.