Relating Almen intensity to residual stresses induced by shot peening: a numerical approach

Shot peening is a surface impact treatment widely used to improve the performance of metal parts and welded details subjected to fatigue loading, contact fatigue, stress corrosion and other damage mechanisms. The better performance of the peened parts is mainly due to the residual stresses resulting from the plastic deformation of the surface layers of the material caused by the impact of the shot. Shot peening intensity is usually quantified by means of the Almen-scale, which measures the residual arc height of a strip made of a specific material, and of a pre-defined size. The scale does not, in other words, apply solely to the residual stress field of a component of unspecified material and size. In this paper, a finite element to predict the residual stresses induced by shot peening in a metal part and to relate these stresses to Almen intensity is proposed; the aim is to provide the designer with a useful tool with which to choose the optimal treatment parameters with respect to the mechanical behaviour of the peened parts. Experimental measurements of residual stresses and a comparison with existing experimental data validate this approach.