Effect of stress relief groove shape on fretting fatigue strength and index for the selection of groove shape

Stress relief groove has been used to improve the fretting fatigue strength of fitted part between mechanical components. However, the effect of groove has not been fully understood and there are not enough investigations to determine the optimal groove shape. In this study, the evaluation of fretting fatigue strength of specimens which have various shapes of stress relief groove was conducted by fretting fatigue tests and FEM analyses in order to find an index for the selection of groove shape. The groove shape was changed systematically with parameters of groove radius R and tangential angle θ. In the fretting fatigue test, fatigue limit of grooved specimen had a peak with increase of θ. The maximum improvement of fatigue limit was achieved at the transition point of the failure mode from the fretting fatigue at contact part to the fatigue at groove root. It was experimentally shown that fatigue limit had a good correlation with the parameter θd, where d is the groove depth. FEM analyses were done to understand the effect of stress relief groove. It was found that the fretting fatigue limit of grooved specimen could be evaluated using the peak axial stress near the contact edge. The estimation of fretting fatigue limit using a relationship between K_t/K_t0 and θd gave a good correlation with the experimental results and it would be a useful method to select the optimal groove shape.