## 3 Tests Results  
### Friction and Wear  
In order to analyze the impact of varying test pressures on the tribological wear characteristics of the three-layer composite bearing bush, a simulated test was conducted for 3 h for each group. Figure 4 displays the wear diagram of the SCF-modified bearing bush under different test pressures. From Figure 4, it can be observed that the wear caused by the roller on the bearing bush is irregularly distributed along the axis direction of the bearing bush. The wear area near the end face of the bearing is larger, and with the continuous increase of the test pressure, the wear area on the bearing surface gradually expands. In the wear area of the SCF-modified bearing, there are no significant wear marks, and the morphology of the ear surface is relatively smooth, with some debris. Additionally, there are a few pits on the material surface, which result in the formation of local transfer films, indicating that the primary wear mechanism is adhesive wear. The frictional torque of the SCF-modified bearing bush under the different test pressures is shown in Figure 5.  
As depicted in Figure 5, a moderate increase in experimental pressure is accompanied by a corresponding rise in friction torque. However, a non-trivial observation emerges where the friction torque at 25 MPa does not exhibit a proportional rise with the increment in testing pressure. Instead, it displays a plateau or even a decrementary behavior, suggesting a deviation from the conventional linear relationship. The frictional torque curve's trend change is influenced by a multitude of factors, including but not limited to tribological surface topography, interfacial effects, and wear mechanisms. These factors can act independently or in combination, necessitating a detailed analysis that takes into account experimental conditions and material properties for a comprehensive understanding. \begin{table}
\begin{tabular}{c c c} \hline
**No.** & **Operating Pressure/MPa** & **Rotational Speed/rpm** \\ \hline
1 & 15 & 50 \\
2 & 20 & 50 \\
3 & 25 & 50 \\
4 & 30 & 50 \\ \hline \end{tabular}
\end{table} 
Table 2: Variable pressure test conditions table. \begin{table}
\begin{tabular}{c c c} \hline
**No.** & **Operating Pressure/MPa** & **Rotational Speed/rpm** \\ \hline
1 & 28 & 0.8 \\
2 & 30.5 & 0.8 \\
3 & 33 & 0.8 \\ \hline \end{tabular}
\end{table} 
Table 3: Low speed and heavy load test conditions table. As the text pressure continues to rise, the pressure experienced by the three-layer self-lubricating bearing bush plate naturally increases. Due to its relatively soft nature, it is susceptible to compressive deformation under increased pressure. The compactness of the self-lubricating layer is enhanced, and the fibers filled in the self-lubricating layer can be better embedded in the PEEK matrix. This prevents wear from fractured fibers, subsequently contributing to a reduction in the friction coefficient of the three-component composite journal bearing. Therefore, when the test pressure reaches 25 MPa and above, the bearing bush surface is not easy to accumulate, and it is easier to increase the interface slip and form a lubricating film. Figure 4: The SCF modified bearing bush wear diagram: (**a**) wear at 15 MPa pressure; (**b**) wear at 20 MPa pressure; (**c**) wear at 25 MPa pressure; (**d**) wear at 30 MPa pressure. Dashed line: the wear range, arrow: the direction of the grinding mark. Figure 5: Frictional torque curves of SCF-modified bearing under the different test pressures. It is worth noting that Figure 5 shows the frictional torque drop at 7000 s for the case of 25 MPa. The addition of SCF filled the holes between the PEEK and PTFE molecular chains fully. With the progress of friction tests, the area of exposed carbon fibers in the interface began to grow, where the carbon fibers' surface, grafted with numerous active functional groups, had notably improved its surface wettability, thus enhancing the shear strength between layers of the carbon fiber composite material significantly [30; 31; 32].