Numerical Simulation Research For Compressive Residual Stress Field And Surface Roughness Of Shot Peening

Shot peening is a surface strengthening technology, which can significantly improve the fatigue life of the workpiece and is widely used in industry. It improves the fatigue life by the appearance of the compressive residual stress in surface layer, the changes of surface roughness and surface material microstructure, in which the compressive residual stress in surface layer is now recognized as the main strengthening factor. Though the change of surface material organization is beneficial to improve the fatigue life of the workpiece, the influence is relatively weak. According to the extent of impact on fatigue resistance, the three factors mentioned above can be sorted as follows:the compressive residual stress, the surface roughness change, the surface material organization change. Hence, in this article we mainly study the residual stress and surface roughness. In conventional shot peening simulation model, which are micro model, the number of shots are inadequate and its distributions are in a regular array. In this paper, the SPH (Smoothed Particle Hydrodynamics) coupling FEM (Finite Element Method) method is applied to establish the new macro stochastic model, which can make the simulation more in line with the actual shot peening process. The previous simulation considers the influence of a single independent parameter on residual stress respectively, and rarely involves in surface roughness.Firstly, the FEM micro model is established by using LS-DYNA and orthogonal experiment method, and is verified by comparing with the experimental results. The comprehensive evaluations of the residual compressive stress layer depth, the surface residual compressive stress, the maximum residual compressive stress value depth and the maximum residual compressive stress value were obtained by means of comprehensive scoring method. Through comprehensive evaluation range analysis, the overall changing extents of the shot peening technological parameters, such as shot diameters, impact angles, impact velocities, overlap rates, impacting frequencies on the same position, the frictional coefficient between target and impact shots, shot’s material properties, were clarified and the optimal parameter combination was obtained through analyzing the diagrams of influential factors from the simulated results, which was verified by further simulation.Secondly, the SPH coupled FEM macro model is established to simulate shot peening process. By MATLAB programming to deal with the shots space coordinates, a random shot peening model with lots of shots impacting the workpiece surface was built. The saturation time of shot peening, the influence of impact angle and mass flow on the residual stress field were analyzed. The results show that with the increase of impact velocity, the time of reaching saturation is shorter. With the increase of impact angle and mass flow, the residual compressive stress is improved. But the residual stress field remains unchanged when the mass flow reaches to a certain extent.Finally, the FE model with more shots is established to study the influence of shot peening parameters on surface roughness, which is verified by FE model with single shot. The results show the surface roughness decreases with the increase of shot peening coverage. But the surface roughness remains unchanged when the coverage reaches to a certain extent. With the increase of impact velocity and shot size, the value of surface roughness increases.