Numerical simulation of shot peening

Shot peening leads to an improvement of fatigue behavior due to the compressive residual stresses developed. There are many parameters, mainly the velocity and the radius of the shot as well as the material parameters, influencing the results in a very complex manner. In order to minimize the effort required to adjust the process, - besides experimental work -, analytical methods as well as the Finite Element Method (FEM) have been used to investigate die process. In this paper a numerical approach will be introduced in order to predict the development, magnitude and distribution of the residual stress state in accordance with the above named parameters. As a first step, axisymmetric models are used to simulate the very short term elastic-plastic deformation process caused by normal impacts of up to 5 spheres on the same location of the surface of a work-piece. In a second step, the effects of adjacent shots are investigated applying a 3D-FE model. With this model, it can be shown how adjacent shots influence the residual stress state developed by former shots, and that the final residual stress state in the surface of the work-piece is inhomogeneous. Simulating a stepwise etching process of the surface of the work-piece reveals that this procedure leads to an increasingly homogenous residual stress state. Etching die surface is necessary to measure the residual stresses experimentally using the x-ray diffraction method. The residual stresses calculated show good agreement with experimental results obtained from peening samples made of spring steel.