By using the specimens of press-fitted part of axles which were cold surface-rolled under various rolling pressures, the relations among its mechanical properties, surface residual stress and fatigue strength, and the change in surface residual stress during the process of fatigue have been studied.
The results obtained are as follows.
(1) The fatigue strength increased linearly with the increase in rolling pressure. For the specimen of mean Hertz pressure 2.83×103MPa, the fatigue strength was 277MPa and its increasing rate relative to that of the normalized specimen was 216%.
(2) The fatigue strength increased as the work-hardening volume and surface compressive residual stress increased, and linear correlations existed between the fatigue strength and these quantities.
(3) The surface compressive residual stress decreased with stress cycle. It decreased linearly to the logarithm of number of stress cycles at the outside of the fitted part, and decreased curvilinearly at the inside of the fitted part. The decreasing rate at the inside of the fitted part was over two times faster than that at the outside. As cyclic stress increased, the decrease of surface compressive residual stress became more notable.
