Relaxation of Shot Peening Induced Compressive Stress during Fatigue of Notched Steelsamples

Abstract

This paper presents an experimental investigation of the surface residual stress relaxation behaviour of a shot peened 0.4% carbon low alloy steel under fatigue loading. A round specimen with a circumferential notch and a notch factor Kt = 1.75 was fatigue loaded in both shot peened and ground conditions. Loading conditions included axial fatigue with stress ratio R = −1 and R = 0 and also R = −1 with an additional peak overload applied at 106 cycles. Plain unnotched shot peened specimens were also fatigue loaded with stress ratio R = −1. The results show how the relaxation is dependent on load level, how the peak load changes the surface residual stress state, and that relaxation of the smooth and notched conditions is similar. Two different shot peening conditions were used, one with Almen intensity of 30–35A (mm/100) and another of 50–55 A (mm/l00).