Quantifying the mass reduction enabled by an optimized residual stress state for components subjected to torsional fatigue

Given the demand for components with high load carrying capacities, driven by the advent of mobility electrification, many studies have identified surface integrity as one of the critical areas affecting the performance of components in future powertrain systems. It is well known that residual stresses have a direct impact on many mechanical properties in components, such as static and fatigue resistance, and can act in a beneficial or deleterious way. However, due to its complex nature, this knowledge is not properly incorporated into design standards and manufacturing requirements, often serving as an additional safety factor in relation to the project. This investigation’s objective is the quantification of volume/mass reduction gains on samples submitted to torsional fatigue tests when residual stresses are considered since the design phase. Samples with different diameters were manufactured in a high cleanness steel, using the conventional manufacturing chain applied to rotary machine elements, composed by machining, case hardening, shot peening and grinding. Also, a final process of isotropic superfinishing was considered to mitigate the influence of topography heterogeneities among samples in the fatigue results. The induction of the optimized residual stress was performed by distinct shot peening configurations among the samples of distinct diameters. The final residual stresses and the actuating stresses were coupled for each sample in such a way that the original and the modified geometries have the same equivalent stress, which is assumed to represent the same fatigue life. The expected results involve obtaining at least two similar shapes, both with the same torsional fatigue life, however with reduced mass/volume induced by an optimized residual stress during the manufacturing process, especially by the controlled shot peening process.