Improving the Fatigue Strength of Fillet Welded Joints by Toe Grinding and Wire Peening (Report 2)

Abstract

Various mechanical methods of improving the fatigue strength were investigated by testing the base plate and cruciform fillet welded joint specimens of 40 kg/mm²-80 kg/mm² class steels. The results obtained are summarized as follows:
1) If a peening condition is suitable to a material, the compressive residual stress induced by peening increases as a yield strength increases. As the ratio of applied cyclic stress range to absolute value of the compressive residual stress decreases, the waste of compressive residual stress by applied cyclic stress decreases and the effect of improving a fatigue life (strength) increases. Therefore, the peening effect can increase with incresaing the yield strength of material.
2) It is possible to consider that a suitable condition of peening is to add the compressive residual stress as large as a yield strength of the material used, and that ari over peening ravages a surface, and may rather result in a reverse effect.
3) As a result of increasing the yield strength of a weld toe and inducing. the compressive residual stress to a weld toe, by peening., a root failure occurs sometimes in the case of non-load-carrying type cruciform, fillet welded joint similarly in thee case of load-carrying type fillet welded double tee joint. Therefore, it is necessary to consider the critical leg length according to a treating condition of a weld toe, in a joint design.