Simulation of residual stresses by shot peening

Shot peening is a cold working process in which small spherical parts called shots are blasted on a surface of a metal work-piece with velocities up to 100 m/s. This treatment leads to an improvement of fatigue behavior due to the developed compressive residual stresses and also to an increase of the surface hardness due to the cold working effect of shot peening. The aim of the paper is to simulate this process with the help of the finite element method in order to predict the development, magnitude and distribution of the residual stresses in accordance with the parameters, which are, e.g. shot velocity, shot diameter and material parameters. In the first step an axisymmetric model is used to simulate the perpendicular impact of an elastic sphere against an elastic-plastic surface. Due to the large plastic deformations, 9/3 mixed formulation elements are used instead of the usual nine-node displacement formulated elements, which are not well suited for this task. In a second step it is shown how the results of the axisymmetric approach can be transformed into a three-dimensional model in order to investigate the effect of adjacent shots. (C) 1999 Elsevier Science Ltd. All rights reserved.