Fatigue strength improvement methods by treating the weld toe

In this study, fatigue strength improvement methods of weld joints, such as TIG-dressing, hammer peening and burr-grinding are discussed with T-form fillet welded joint specimens. Concerning the crack initiation life, crack propagation life, and improvement mechanism of fatigue strength, fatigue testing, FEM analysis, measuring residual stresses, observation of crack surface and fracture mechanics approach are carried out. As a result of fatigue testiness, fatigue strengths of all types of improved specimens, especially burr-grinded specimens are higher than as-welded specimens. Effect of decreasing stress concentration by developing the configuration of welded toe is found only at 1 mm thick from treated surface, so that fatigue strength improvement effect of TIG-dressing and burr-grinding is observed only during fatigue crack length is small (N_c). On the other hand, by hammer peening high compressive residual stresses are induced about at 4 mm thick from treated surface so that improvement effect is obtained during crack propagation life (N_p). However, hammer peening induces ditch which is about from 0.2 to 0.4 mm deep from the surface and the ditch work as source of stress concentration like under-cut, improvement effect of hammer peening is not found during crack is small (N_c).