## 4 Friction and Wear Mechanism  
Figure 14 shows the deformation of the standard pistons and textured pistons 1-27. It can be seen that the maximum deformation of the piston was concentrated at the edge of the rubber part. The distribution of deformation was in a ring shape, decreasing gradually from top to bottom. The wear of the piston was mainly concentrated in the position with large deformation, which is consistent with the results of the wear test. Compared with the standard pistons, the maximum deformation of the textured pistons was reduced to some extent. The primary cause for this occurrence is that the presence of cylindrical pit arrays can provide more compression space on the piston surface, and each cylindrical pit structure can withstand a higher degree of deformation, alleviating the phenomenon of concentrated deformation distribution at the piston's lip. We performed an in-depth analysis of textured pistons 4, 13, 22 and 25, with their maximum deformation data (\(x\)) presented in Table 5. It becomes apparent that \(x\) for these four pistons ascended with an increase in \(X\). Specifically, piston 4 witnessed the highest reduction in its maximum deformation, tallying a decrease of 25.49%. Meanwhile, the other three pistons showed less pronounced reductions, with all falling under 10%, specifically at 7.25%, 2.51% and 1.41%. Figure 13: Time–temperature curve. Figure 15 shows the equivalent stress of the standard pistons and textured pistons 1-27. The maximum equivalent stress of the standard piston appears on the upper surface. Excessive equivalent stress can cause serious extrusion and premature failure of the piston. The maximum equivalent stress of the piston with cylindrical pit arrays is distributed near the cylindrical pit, which can reduce the phenomenon of piston squeezing. The maximum equivalent stress of textured pistons 1-9 was smaller than those of the standard pistons. The maximum equivalent stress of textured pistons 19-27 increased to a certain extent compared with the standard pistons, while the equivalent stress of textured pistons 10-18 increased in some cases and decreased in others. This may be related to the depth of the cylindrical pit texture. Therefore, in the analysis of the equivalent stress of the textured piston, we concluded that \(H\) for the textured pistons had the most obvious impact on the equivalent stress. \(H\) in this article should be less than 0.5 mm to reduce the equivalent stress of the textured piston and reduce the impact of the cylindrical pit texture array on the surface strength of the piston. We performed an in-depth analysis of textured pistons 4, 13, 22 and 25, with their maximum equivalent stress (\(y\)) presented in Table 5. Compared with the standard piston, \(y\) for piston 4 was significantly reduced, while \(y\) for pistons 13, 22 and 25 did not change much. The \(y\) value of textured piston 4 decreased by 15.67%, while \(y\) for the other three textured pistons increased by no more than 10%. Since the equivalent stress distribution of the textured piston will be dispersed to each cylindrical pit texture, the depth and size of the cylindrical pit array will significantly affect the equivalent stress of the piston. Too deep and too large of a cylindrical pit size will destroy the strength of the  
Figure 14: Deformation of standard and textured pistons. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(\mathbf{Y}\) & \(\mathbf{\xi}\) & \(\mathbf{4}\) & \(\mathbf{13}\) & \(\mathbf{22}\) & \(\mathbf{25}\) \\ \hline \(\mathbf{x}\) (mm) & 1.1701 & 0.8607 & 1.0713 & 1.1261 & 1.1388 \\ \(\mathbf{y}\) (MPa) & 0.85131 & 0.71788 & 0.92184 & 0.88829 & 0.93348 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Maximum deformation and maximum equivalent stress. piston's surface to a certain extent, thus affecting the service life of the piston. Therefore, our optimized piston needs to be verified in a life test. As shown in Figure 16, the contact pressure contour maps of the 27 textured pistons and the standard piston are presented.