A Finite Element Methodology for the Fatigue Analysis of a Gear with Nitriding Treatment Subjected to a Potential Overload

Nitriding creates compressive residual stress on the surface to enhance hardness and improve the fatigue life of mechanical components, such as gears. However, subsurface tensile stresses are induced and must be evaluated to ensure structural reliability potentially causing damage to nucleate beneath the surface. In this article, a case study has been analysed in which the application of a high overload during meshing leads to the plastic deformation of the tooth, and consequently to a redistribution of residual stresses. Specifically, the study focused on how this alteration of the stress state, previously generated by nitriding, affects the fatigue resistance of the component. The analysis was carried out using Finite Element simulations. First, the residual stresses induced by the treatment were estimated, and then simulated. After that the plasticizing load was applied. Several meshing configurations were simulated to identify critical zones of plasticization and stress redistribution. Results highlighted that the most intense plasticization regions were on the boundary between treated and untreated areas. Finally, a standard load history was applied to the component subjected to the overload to evaluate its fatigue behaviour. The proposed methodology effectively captures how residual stress alteration reduces fatigue resistance, offering a robust approach for fatigue forecasts.