Determination of material-specific deep rolling parameters in consideration of surface integrity and very high cycle fatigue strength of shafts

Deep rolling can effectively increase the very high cycle fatigue strength of gear shafts. However, selecting the optimal deep rolling force and feed is challenging, as hardening, residual stress state and surface roughness interact in complex ways and preliminary testing is time-consuming and costly. This study provides material-specific recommendations regarding deep rolling force and feed based on theoretical and experimental investigations. Hertz’s theory is used to determine the contact conditions during the rolling process in order to evaluate the local pressures and overlap factors. The experimental part comprises deep rolling and fatigue strength tests. The deep rolling tests on round bars indicate the material-dependent maximal values for contact pressure and overlap factor, taking into account the resulting surface roughness, which constitutes the upper limit of the process window. Residual stress measurements and staircase tests on notched specimens allow the estimation of the lower pressure limit ensuring the intended fatigue strength improvement. The objective of this work is to introduce a material-specific process window for the deep rolling of shafts as a novel contribution and to offer practical guidance on setting optimal machine parameters.