Residual stress distribution and evolution in gear shaft journals induced by mechanical roll hardening: experimental characterization and numerical prediction

Abstract

To mitigate residual tensile stresses in the surface layer of machined 30CrMoA gear journal shafts, which readily initiate fatigue cracks and degrade in-service reliability, this study investigates a localized deep rolling hardening process for the journal diameter. Combining finite element simulation with X-ray diffraction residual stress measurements, the residual stress distribution in the journal after rolling is characterized, and the effects of key process parameters (rolling depth, workpiece rotational speed, and feed rate) on the magnitude of residual compressive stress and the strengthened layer depth are systematically examined. A central composite design-based response surface methodology is then employed to develop predictive models for residual stress and layer depth, enabling multi-objective optimization of the rolling process. The results demonstrate that deep rolling generates a stable, graded residual compressive stress field within the localized surface layer of the journal, with the peak compressive stress occurring approximately 0.20 mm beneath the surface, while the underlying matrix exhibits weak equilibrating tensile stresses. Rolling depth is identified as the most influential parameter and pronounced coupling and saturation effects among the parameters are observed. An optimal parameter combination is determined and experimentally validated: under the optimized conditions, both the magnitude of residual compressive stress and the strengthened layer depth are markedly improved, with the deviation between simulated and experimental results remaining below 8.0%. The established parametric model accurately predicts the localized residual stress state in rolled 30CrMoA journals, providing theoretical guidance and technical support for the surface rolling strengthening of gear journals.