## 4 Simulation Analysis of Roughness on Shot Peening Residual Stress and Surface Deformation
### Effect Analysis of Roughness on Residual Stress and Deformation of Shot Peening
#### 4.1.5 Analysis of Average Residual Stress Distribution of Different Roughness Surface  
Figure 8 shows the distribution of the residual compress stresses-counting position on the target material surface after shot peening. Table 5 shows the average range of residual stress distribution. It can be further proved that surface roughness directly affects the stress distribution. With the increase of surface roughness, the value of residual stress on the surface caused by shot peening also increases; however, the range distribution of residual compress stress decreases. The axis of symmetry is the axis where the pellet impact causes the deepest position of the pit. After shot peening, the distribution range of residual compress stress on a small roughness surface is wide and approximately symmetrical; the surface roughness is 0, 10, and 16 \(\upmu\)m, with a range of 0.87, 0.99, and 0.87 mm, respectively. The distribution range of surface residual compress stress on large roughness surfaces is relatively narrow, and the symmetry of residual stress change is relatively weakened. The residual compress stress distribution ranges of 24 \(\upmu\)m and 29 \(\upmu\)m rough surfaces are 0.75 mm and 0.54 mm, respectively. When the surface roughness is 0 \(\upmu\)m and 10 \(\upmu\)m, after shot peening, the residual compress stress shows a changing trend of \"the residual stress near the axis of symmetry is relatively low, then increases, and finally decreases\". Figure 6a,b reflect the phenomenon. The phenomenon indicates that when the surface is smooth, or the surface topography is relatively simple, the surface morphology has little effect on the surface material accumulation after impact. The combined effect of impact and material accumulation leads to the distribution regulation of \"the residual compress stress near the axis of symmetry is relatively low, then increases, and finally decreases\" when the target material has small surface roughness. However, when the surface roughness is larger than 10 \(\upmu\)m, surface topography is relatively complex, the maximum residual compress stress appears at the impact center, and the residual stress produced by impact also has the characteristics of the asymmetric distribution. Figure 8: Distribution of surface residual stress. According to the analysis of Figures 7 and 8, the changing trends of residual stress and displacement produced by impact both increase with the increase of surface roughness. The residual stress caused by the impact is the fundamental cause of target material surface displacement. It can be inferred that the surface roughness and topography are the main reasons that affect the surface deformation amount after the pellet impact. In contrast, the residual stress produced by contact form and contact position between pellet and surface is the direct reason for surface deformation and surface material accumulation. Based on the simulation results, it can be inferred that, during the process, the surface finishing treatment of processed parts will affect the surface roughness of parts after shot peening. Under the same machining condition, shot peening would have a specific repair effect on the large roughness of surface topography; moreover, reducing the surface roughness of workpieces could get a better stress strengthening effect. Although the workpieces with the large surface roughness would have a large surface material deformation, there still needs to be attention to the fact that when the surface roughness of the workpiece is over large, the shot peening could not achieve the expected repair effect due to the depth of the wave trough of the workpiece surface topography being large. Therefore, during the process before shot peening, while increasing the surface roughness of the workpiece, it should also make sure that the roughness of the machined workpiece is within a certain range. For the workpieces with small roughness and simple surface topography, the surface material displacement produced by shot peening is relatively low.