Fretting fatigue and shot peening: a multiaxial fatigue criterion including residual stress relaxation

Fretting fatigue damage is a typical material damage arising in mechanical components. In such a damage condition, surface cracks can initiate at the surface contact zone, and under a fluctuating loading they can grow up to the complete failure of the component, resulting in a catastrophic failure. In order to prevent/mitigate fretting fatigue damage, shot peening is widely used in mechanical components. The improvement due to shot peening is related to different factors, but the main one is the compressive residual stress field produced by such a treatment in a region near the contact surface. Unfortunately, both the uncertainty in measurements and stability (relaxation) of residual stress field, make shot peening effects difficult to be included in models aimed to the estimation of fatigue life. Due to this lack in the literature, especially relatively to the fretting fatigue field, in the present paper a new fretting fatigue model, that is able to consider shot peening residual stress and its relaxation, is presented. A 3D elastic-plastic finite element model, which incorporates the shot peening residual stress and its relaxations, is employed. The results obtained, in terms of stress field, are used as input data of a multiaxial stress-based criterion to estimate both fatigue lifetime and crack initiation direction.