Influence of stress-relieving by vibration as compared with post-weld heat treatment on the fatigue behaviour of repair welds

The most common method for relieving residual stresses is post weld heat treatment (PWHT). PWHT is used in cases where machining of welded components and castings with high residual stresses may result in undesired distortions. The beneficial influence of PWHT on fatigue is significant at negative R- values and low stress ranges. Compared to PWHT, vibrational stress relief (VSF) has the potention for significant advantages: reduction of cost, absence of scale, no metallurgical consequences etc. The aim of the present research was to determine the effectiveness of VSR compared to PWHT, especially for welded structures with repaired welds. In the investigations, several test series were carried out, where welded components indifferent fabrication states (as welded, vibrated after welding, heat treated after welding and preloaded after welding), were submitted to fatigue loading. It is found that due to the absence of sound and common accepted guidelines and quality criteria, the success of vibrational stress relief is quite uncertain. Furthermore, it is found that in fatigue loading, VSR probably has no significant beneficial effect. During the first load cycles, about the same "stress relief" occurs as during VSR. Only in case of very low stresses and low R-ratios, VSR may have any positive effect on the fatigue life of welded structures.