Fatigue on Shot-Peened Gears: Experimentation, Simulation and Sensitivity Analyses

The present paper deals with fatigue experimentation and with the application and improvement of predictive models; in addition, a sensitive analysis is performed on the main factors related to the shot-peening treatment and on the efficiency of the aforementioned models. The research involved gears, made of high-strength steel and carburised, quenched, ground, shot-peened and superfinished. The experimental campaign initially dealt with the investigation into the influence of isotropic superfinishing; the attention was then focused on shot peening and how to optimise the fatigue limit, by a suitable choice of operative parameters. The option of duplex peening for further fatigue improvement was also considered. Results concerning component residual stress distributions and fatigue limits were then processed by investigating their sensitivity with respect to driving factors, namely the shot diameter and the Almen intensity. Two theories for fatigue prediction (the method of the relative stress gradient and the theory of critical distances) were reviewed for application to shot-peened components, with a comparison between experimental and numerical results. A comparative analysis was then performed on the two theories, on the basis of the number of data inputs, advantages and drawbacks, while sensitivity analyses focused on how uncertainties affecting input data propagate to predictive results.