Effect of shot peening on the improvement of durability of bevel gear

Shot peering generate compressive residual stress, which reduces repeatedly assessed tension stress and increase fatigue life. In this paper, the fatigue characteristics are evaluated according to shot peening condition for the real differential gear. The specimen is a straight bevel gear which transmits rotation of engine to running wheel and it is caburized. The bending fatigue test was done by the jig of our own making. The peening time was changed to find the best condition for the long fatigue life time. Fractography of specimen was analyzed by SEM to detect the location of initial crack. The experimental results show that the optimum peening condition is at 65m/s of shot ball speed and 8min of shot peening time. From the SEM image, the location of initial defect and direction of crack propagation were found.