## 4 Simulation Analysis of Roughness on Shot Peening Residual Stress and Surface Deformation
### Analysis of Residual Stress and Deformation of Different Impact Positions in Rough Surface
#### 4.2.1 Analysis of Surface Deformation in Different Impact Positions  
Four common target morphologies are selected in the process of shot peening, which are pit, peak, half slope, and ridge; the surface material displacement and nephogram characteristics of the target material surface after shot peening are shown in Figure 9. As shown in Figure 9, the surface topography of the target material has a noticeable influence on the impact effect of shot peening. Under the same surface roughness, displacement of the pit under the impact of shot peening is the smallest, the deformation displacement of the impact is the largest at the peak; the displacement of impact on the ridge and the half slope is not fixed, which the surface roughness is 10 \(\upmu\)m the displacement at the half slope and is larger than that at the ridge, while the surface roughness is 16 \(\upmu\)m the displacement at the half slope and is smaller than that at the ridge. With the increase of surface roughness, the displacement at the pit produced by pellet impact gradually decreases, and the displacement produced by pellet impact gradually increases at the peak. The displacement on the ridge and the half slope is still not fixed, and the surface roughness is 24 \(\upmu\)m the displacement at the half slope and is smaller than that at the ridge, while the surface roughness is 29 \(\upmu\)m the displacement at the half slope and is smaller than that at the ridge. With the increase of surface roughness, the accumulation of target material surface after impact also shows an asymmetric trend. Through the comparison of the nephogram, when the surface roughness is 10 \(\upmu\)m, the distribution of residual stress in the nephogram has the trend of \"first increases and then decreases\", but the stress concentration caused by the surface topography appears in the pit. When the surface roughness is 16 \(\upmu\)m, the residual stress distribution trend in the nephogram shows different trends affected by the impact position, which is that the maximum residual stress at the ridge and pit is concentrated in the impact center of the impact, while the trend of first increases and then decreases and still appears at the peak and half slope. The changing trend of residual stress also appears after impact at the half slope. When the surface roughness is greater than or equal to 24 \(\upmu\)m, the maximum residual stress concentrates at the impact center. When the surface roughness is 29 \(\upmu\)m, at peak and half slope, the pellet leaves the surface after the first impact, which would impact the other position of the target material surface, causing the secondary impact as shown in Figure 9d. Under the condition of the surface roughness of the target material is relatively large, and the surface topography is relatively complex. When the pellet impacts on the half slope of surface topography, the reflect angle of pellet is relative large after impact, making the pellet stick to the target material surface and leave the impact center; during the process of the pellet leaving the impact center, the pellet impacts on the bump of target material surface, causing \"secondary impact\". When the pellet impacts on the peak of  
Figure 10: Distribution effect of residual stress. (**a**) 10 \(\upmu\)m; (**b**) 16 \(\upmu\)m; (**c**) 24 \(\upmu\)m; and (**d**) 29 \(\upmu\)m.  
target material surface, the pellet leaves the impact center with a certain angle, the pellet may have an impact on the position higher than the impact center, which would also cause the \"secondary impact\". The accidental appearance of \"secondary impact\" phenomenon means that when the surface roughness of the workpiece is over large, the pellet which finishes the processing will have a certain effect on the subsequent processing during the shot peening process. The displacement on the position of the ridge shows the trend of first increasing and then decreasing with the increase of target material surface roughness and surface topography.