## 3 Results of Finite Element Analysis of Pressure Plates
### Stress Field Analysis of Pressure Plate  
To better understand the fundamental mechanism of this inner concave deformation of pressure plate, we placed an emphasis on the equivalent von Mises stress distribution of the pressure plate is  
Figure 8: Relative displacement curve of axial deformation at the bottom of pressure plate. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Time (s) Displacement (mm)** & **Constraint 1-Relative Axial Displacement (mm)** & **Constraint 2-Relative Axial Displacement (mm)** \\ \hline
12 & 0.430 & 0.568 \\ \hline
24 & 0.623 & 0.790 \\ \hline
42 & 0.833 & 1.040 \\ \hline
60 & 0.979 & 1.222 \\ \hline
748 & 0.007 & \(-\)0.136 \\ \hline
1436 & \(  
emphasized. Particularly, the equivalent von Mises stresses at four key points of the cross section of the pressure plate, labeled as a, b, c, and d in Figure 9, were analyzed, where, a and b are the upper corner points of the cross section, c is the inner corner point of the cross section, and d is the outer corner point of the cross section of the pressure plate. Through the finite element analysis, the equivalent von Mises stress of the above four key points as a function of time under the first type of constraint conditions is obtained, as shown in Figure 10 and Table 2. The equivalent von Mises stress under the second type of constraint conditions is also obtained, as shown in Figure 11 and Table 3. The comparison of the stress for the two types of constraints is shown in Figure 12.  
Figure 10: Stress at the four critical points of the pressure plate under the first type of constraint. Figure 9: Key points on the pressure plate as well as the axial and chassis surfaces. It can be seen from Figures 10-12 that the tendency of the equivalent von Mises stress of the four key points of the pressure plate is generally the same as that of the relative axial displacement of the pressure plate shown in Figure 8 for each type of constraints; that is, the equivalent von Mises stress increases during slipping (heating) and decreases during separation (cooling). For the first type of constraints, at ~748 s, the equivalent von Mises stresses at the all four points decrease to 5 MPa (seen in Table 2), and the difference between these stresses value is very small. Starting from 748 s, the equivalent von Mises stresses of the four key points are further reduced to ~1 MPa, and they are almost uniform at ~0.5 MPa (seen in Table 2) later. This quantitative trend of \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Time (s)** & **Stress at Key Points (MPa)** & **a** & **b** & **c** & **d** \\ \hline
12 & 31.834 & 16.982 & 13.566 & 50.807 \\ \hline
24 & 32.592 & 20.522 & 27.863 & 64.417 \\ \hline
42 & 35.987 & 26.997 & 48.689 & 73.416 \\ \hline
60 & 37.227 & 30.551 & 65.793 & 64.478 \\ \hline
748 & 16.822 & 1.8175 & 14.516 & 6.4262 \\ \hline
1436 & 23.431 & 2.7072 & 20.983 & 11.112 \\ \hline
2468 & 24.489 & 2.866 & 22.050 & 11.626 \\ \hline
3500 & 24.585 & 2.877 & 22.147 & 11.620 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Stresses at the critical points of the pressure plate under the second type of constraint. Figure 11: Stress at the four critical points of the pressure plate under the second type of constraint. the equivalent von Mises stresses is also identical to that of the relative axial displacement of friction surface of the pressure plate, indicating that the displacement of the pressure plate is determined by its stress state. For the second type of constraints, the stress state of these four key points shows a significant difference during the natural cooling process compared with the first type of constraints. Unlike the first type of constraints, at \(\sim\)748 s, the equivalent von Mises stresses at the four points are relatively high and the difference between these four stress values is also obvious (see Table 3). Particularly, at 748 s and later, theses four equivalent von Mises stresses are also relatively high and not uniform, as under the first type of constraints.