# Friction Behavior of Ceramic Materials for the Development of Bridge-Bearing Friction Materials
## 3 Friction Test Results and Analysis of Ceramic Materials
### Frictional Behavior of Ceramic Materials  
The surfaces of the ceramic materials were visually inspected before and after the friction tests (Figure 4). Despite repeated horizontal movements under the applied contact pressures of 15 and 60 MPa, the surface of the ceramic-friction material remained exceptionally smooth with no observed defects or damaged areas. The superior hardness of ceramic materials contributes to their high wear resistance, demonstrating that, even under strong contact conditions owing to high vertical loads, ceramics maintain significant resistance to wear from horizontal frictional movement. This indicates that the ceramic materials exhibit excellent durability and stability against abrasive forces, even under rigorous loading conditions.  
The friction test results for the ceramic materials with different roughness coefficients and loads are shown in Figure 5. For ceramic-friction materials with a roughness coefficient of 0.8, the results showed a consistent trend without a significant variation in the horizontal load, even as the number of friction cycles increased under contact pressures of 15 and 60 MPa. This indicates the stable frictional behavior of the ceramic material during the repeated friction tests. The average COF for the ceramic material with a roughness coefficient of 0.8 was determined to be 0.16 under 15 MPa and 0.13 under 60 MPa.  
For ceramic materials with a roughness coefficient of 0.027, the horizontal load progressively increased with the number of friction cycles, as observed in the horizontal load-horizontal displacement curves. Initially, the COF was approximately 0.1. However, it gradually increased with the number of cycles, reaching an average value of 0.16. The increase in the horizontal load corresponded to an increase in the COF, suggesting a diminishing effect of the surface roughness on the frictional performance over time.  
During the initial stages, the friction coefficient of the ceramic material with a roughness coefficient of 0.027 was lower than that of the ceramic material with a roughness coefficient of 0.8. However, as the number of friction cycles increased, the difference decreased and eventually reversed. Although a roughness coefficient of 0.027 theoretically results in a lower COF owing to a smoother surface, the combined effect of the high hardness of the ceramics and strong surface contact under high-load conditions appears to offset the influence of surface roughness at the microscopic level [35]. This effect amplifies the inherent COF of the ceramic material, which is the dominant factor influencing frictional behavior. In conclusion, achieving a low COF through surface polishing to reduce the surface roughness does not yield significant results under high-load conditions for ceramic materials. The intrinsic properties of ceramics, particularly their high hardness and strong contact conditions, overshadow the effects of surface roughness, making surface polishing less impactful in these scenarios.  
Figure 4: Inspecting surface of ceramic-friction material.