Increased Fatigue Strength of Powder Forged Connecting Rods by Optimised Shot Peening

Abstract

Shot peening is a surface treatment commonly used to improve the fatigue life of aircraft, automotive, and other highly stressed structural components. This improvement is attributed to the formation of compressive residual stress in the surface layer of the material by the impingement of spherical media (shot). The compressive residual stress usually decreases the tensile stress created in the component by ‘in service’ external forces and, therefore, increases the fatigue strength of the part. To quantify the improvement resulting from shot peening, the fatigue behaviour of powder forged connecting rods and laboratory test bars from the base material (2%Cu steel), in both the stress free (unpeened) and surface treated (shot peened) condition, were compared. Fatigue data were correlated with the residual stress generated at the surface. The stress magnitude and depth were determined using X-ray diffraction analysis. Optimum processing parameters for shot peening were also determined. Results show a significant increase in the fatigue strength of shot peened laboratory test specimens and connecting rods compared with unpeened bars and rods. PM/0700