Numerical Assessment Of Shot Peening Contribution To The Fatigue Strength Of Gear Tooth Root

Gears are commonly treated with shot peening (SP) and/or case hardening to enhance fatigue resistance. However, their effects are often conservatively assessed using standardized methods, which can limit their optimal application in industrial components. Particularly, the effect of SP over case-hardened gears remains insufficiently explored. Therefore, the present study evaluates the contribution of SP on single tooth bending fatigue (STBF) strength of raw and case-hardened spur gears, commonly used in automotive and heavy machinery industries. In the study four conditions are addressed: (i) untreated, (ii) case-hardened, (iii) shot-peened, and (iv) case-hardened and shot-peened. First, the residual stress field of the corresponding treatment states are estimated by means of high-fidelity numerical models. Then, STBF strength under different loading conditions is assessed by means of a multi-axial fatigue criteria in combination with the theory of critical distances (TCD). The results confirm that SP significantly enhances fatigue strength by inducing compressive residual stresses that delay crack initiation and slow propagation. When combined with case-hardening, SP further improves fatigue resistance, revealing a strong synergistic effect. These findings highlight the need for an optimized surface treatment strategy beyond conventional design methodologies. In addition, they provide valuable insights into fatigue life improvement in shot-peened and case-hardened gears, contributing to the development of more durable and efficient industrial components.