## 6 Conclusions  
In this paper, a rough surface single-shot peening simulation model was built based on W-M fractal dimension theory. The established simulation model is based on the fact that before shot peening, the surface would be pre-processed, which would change the surface roughness and topography of the workpiece. The simulation model built in this paper considered this situation and set the surface as a rough surface, which is closer to the actual processing situation. The surface roughness is chosen as a variable, and surface maximum residual stress and surface deformation are chosen as indicators. The influence law of different surface roughness and different impact positions on shot peening were analyzed by the built simulation model. The established shot peening simulation model takes into account the influence of surface roughness and surface morphology, which makes the shot peening simulation process closer to the actual shot peening process, and can establish a relationship between the impact of shot particles and surface morphology in the shot peening process, which provides a new way for shot peening simulation. 1. Based on the built simulation model, the average maximum residual stress was analyzed; the maximum residual stress on the 24 um surface is 1137.8 MPa after shot peening, which is the largest among all rough surfaces. Meanwhile, the stress caused by impact under the roughness of 24 um surface increases with the increase of surface roughness. When the surface roughness is greater than 24 um, the material deformation of the workpiece is limited, which makes the average maximum residual stress shows a trend of first increasing and then decreasing. 2. The average deformation increases with surface roughness after shot peening, which increases from 10.1 um to 13.1 um, while the distribution range of residual stress decreases from 0.87 mm to 0.54 mm. The width of pits decreases with the increase of surface roughness, which decreases from 0.21 mm to 0.15 mm. The residual stress distribution and the surface material accumulation all have the character of asymmetric distribution after the impact. 3. When the pellet impacts on different positions on the surface with the same surface roughness, it can be seen that large deformation would appear after the pellet impacts at the peak; with the increase of the surface roughness, the deformation at the ridge appears the trend of first increases and then decreases due to ridge at small roughness surface is wider and easy to deform, when the surface roughness is large, the rebound of surface material makes the deformation of ridge relatively small. It is worth notingthat when the surface roughness of the target material is 29 \(\upmu\)m, the \"secondary impact\" appears after a single pellet impact, which would affect the subsequent shot peening. Therefore, in order to ensure the complexity of the surface topography is relatively small, the surface roughness should not be too large. In addition, under the condition of the simulation model in the paper, the optimal initial machining surface roughness should be 24 \(\upmu\)m.
* The shot peening experiments were conducted, and the surface topography and residual stress of processed and unprocessed test pieces were tested. The results show that the residual stress on surfaces polished by 1200# sandpaper, 80# sandpaper and file increased by 17.6%, 16.8%, and 71.5%, respectively; the surface topography test shows that the surface with big surface roughness changes obviously after shot peening. The experiment results mentioned above consist with tend of the rough surface single shot peening simulation results. The errors of residual stress and pit deformation size between the experiment and simulation are less than 20%, which verified the effectiveness of the simulation model. [PERSON] and [PERSON] conceived the idea of this work. [PERSON] and [PERSON] conducted the simulation and shot peening experiment; data curation, [PERSON]; original draft preparation, [PERSON]; review and editing [PERSON] and [PERSON].