# Friction Behavior of Ceramic Materials for the Development of Bridge-Bearing Friction Materials
## 3 Friction Test Results and Analysis of Ceramic Materials  
### Friction Test Plan for Ceramic Materials  
To utilize ceramics as friction materials, an analysis of their friction characteristics is essential, leading to an evaluation of the frictional behavior of the ceramic materials themselves. The friction test was conducted according to the standards for friction materials outlined in the AASHTO LRFD Bridge Construction Specifications (BCS) [31], considering the specifications of the testing equipment and fixed jig standards. The friction material (upper plate) was manufactured with a diameter of 76 mm and a thickness of 5.5 mm, whereas the counter material (lower plate) was produced with dimensions of 130 mm \(\times\) 140 mm and a thickness of 5.5 mm. The fixed jig was designed to securely hold both the friction material and the counter material in place, ensuring precise alignment,  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Properties**} & **Ceramic** & **Stainless** & \multirow{2}{*}{**PTFE**} & **EP** & **UHMWPE** \\  & **(ZrO\({}_{2}\))** & **Steel** & & & \\ \hline Young’s modulus (GPa) & 220 & 210 & 0.41 & 1.3 & 31 \\ \hline Flexural strength (MPa) & 1000 & 515 & 500 & 70–80 & 600 \\ \hline Hardness (HV) & 1550 & 500 & - & - & - \\ \hline \end{tabular}
\end{table}
Table 1: Comparison of properties by material.  
\begin{table}
\begin{tabular}{c c} \hline \multirow{2}{*}{**Component**} & **Result (\%)** \\ \hline ZrO\({}_{2}\) & 94.66 \\ \hline Y\({}_{2}\)O\({}_{3}\) & 5.34 \\ \hline Al\({}_{2}\)O\({}_{3}\) & 0.23 \\ \hline Fe\({}_{2}\)O\({}_{3}\) & 0.001 \\ \hline TiO\({}_{3}\) & 0.001 \\ \hline SiO\({}_{3}\) & 0.004 \\ \hline CaO & 0.001 \\ \hline Na\({}_{2}\)O & 0.003 \\ \hline \end{tabular}
\end{table}
Table 2: Components of ceramic materials.  
minimizing unintended movement during testing, and enabling accurate and repeatable friction measurements [32; 33; 34].  
The testing equipment used was a sliding pad performance evaluation device with a vertical load capacity of 1200 kN, a horizontal load capacity of 250 kN, and a stroke of \(\pm\)100 mm (Figure 3). Friction tests were performed under bridge-loading conditions by applying a vertical contact pressure of either 15 or 60 MPa. The horizontal movement was controlled at a displacement of \(\pm\)12.7 mm from the origin at a speed of 1.058 mm/s. Finally, the COF was determined using the ratio of the vertical force to the horizontal force. To perform and evaluate tribological experiments, a ceramic-friction material with a diameter of 76 mm and a thickness of 5 mm was prepared, along with a rectangular ceramic floor plate designed to allow horizontal movement.  
Factors influencing the frictional behavior of bridge bearings include the inherent COF of the material and the surface roughness coefficient, both of which are critical variables [6]. Given the goal of avoiding lubricant use, surface roughness, which significantly affects frictional behavior, can be optimized through surface polishing to achieve lower roughness coefficients, thereby facilitating the expression of lower friction coefficients. To understand the frictional behavior of the ceramic materials, two surface roughness variables were established based on the polishing processes: 0.8 and 0.027. A surface roughness of 0.8 represents the average value typically achieved through ceramic manufacturing, whereas a surface roughness of 0.027 represents the minimum achievable value through polishing without causing performance degradation.  
Figure 3: Frictional behavior evaluation test.