Effect of compressive residual stress and surface morphology introduced by shot peening on the improvement of fretting fatigue life of TC4

Fretting fatigue is a common phenomenon between contacting components that significantly reduces the life of the specimen due to stress concentration and surface wear. Shot peening is a widely used surface strengthening technique that improves fatigue life by introducing surface hardening and residual stress fields. This study employed a bridge-type pad and flat specimen test setup to investigate the effects of fretting and shot peening under tensile loads ranging from 250 MPa to 850 MPa. Finite element simulations modeled the shot peening process and fretting behavior, incorporating surface morphology changes and near-surface residual stress distributions using a Python script. The Chaboche material constitutive model and ABAQUS subroutines were used to calculate the stress-strain evolution of the specimens under different numbers of cycles. The results indicate that fretting induces significant stress concentration and relative slip at the edges of the contact zone, reducing the fatigue life to only 26.3 % to 58.7 % of that in conventional fatigue. For the shot-peened specimens, the asperities formed on the surface influence the stress concentration and relative sliding distance, while the introduction of residual stresses significantly increases the fatigue life by a factor of 1.38 to 6.72. Finally, based on the characteristics of the fretting stress distribution and the features of the shot-peened specimens, a life prediction model was proposed for fretting fatigue, taking into account the stress gradient across the crosssection. Over 90 % of the data points fall within a 1.5x scatter band.