Application of shot peening to case-hardened steel gears: the effect of gradient material properties and component geometry

Shot peening is a mechanical surface treatment widely utilized to enhance the fatigue strength of gears by surface work hardening and inducing compressive residual stresses while also altering the surface roughness. This study is aimed at developing a detailed numerical model of dual shot peening on case hardened gears by considering the variation of material properties through the thickness. Two different approaches were implemented to estimate the gradient material properties of case-hardened steel. In the first approach, a set of experimental tests and finite element modeling of an indentation were utilized to obtain the stress-strain response of the gradient structure using inverse analysis. In the latter approach, empirical relations were used to adjust the flow stress to the local hardness variation through the thickness. The intricate geometry of the gear also necessitated simulating the shot kinetics on the gear tooth using appropriate impact angles. Various modeling approaches were incorporated to consider the deviation of the impact angle due to geometrical features. The results indicate that a local 3D cubic cell model can be successfully implemented to predict the final distribution of residual stresses and surface roughness. The results are critically discussed in terms of the applied modeling approaches.