## 3 Results and Discussion  
### Permeability in the in-Plane Direction  
Figure 6 shows the permeability in the in-plane direction for each fiber volume fraction. The tests were conducted on two cases with fiber volume fractions of 55% and 60%. The permeability of the fiber in the 90\({}^{\circ}\) direction (having a maximum flow velocity) is K1, and the permeability of the fiber in the 0\({}^{\circ}\) direction (having a minimum flow velocity) is represented by K2. In each measurement, the neat fabric preform and binder-treated fabric preform with a heat treatment during the preforming process were used to investigate the effect of the binder on the in-plane permeability. The average value of each test is indicated, and the error bar shows the maximum and minimum of the sample. As shown in Figure 6 and Table 2, the permeability of the binder-treated fabric preform decreased in every case, regardless of in-plane direction (K1, K2) and the fiber volume fraction. It can be inferred that the treated binder hindered the impregnation of resin in the preform, decreasing the permeability by approximately 80% for K1 and 82% for K2, at a 55% fiber volume fraction, and 80% for K1 and 77% for K2, at a 60% fiber volume fraction. In spite of the consideration of the amount of porosity reduction due to the binder content noted in Table 1, the permeability in the in-plane direction of  
Figure 4: Equipment for measuring the friction coefficient.  
Figure 5: Test cases of the coefficient of friction of carbon fabric.  
the binder-treated fabric preform significantly decreased, which means that the binder treatment changed the permeability characteristics of the fabric preform itself. In addition, the permeability of the fiber tended to decrease as the fiber volume fraction increased in both the K1 and K2 directions, regardless of the binder treatment, and especially for neat fabric, which exhibited a larger decrease (K1: \(-16\%\), K2: \(-28\%\)) than that of the binder-treated fabric. It is assumed that the permeability of the binder-treated preform, which had already been reduced due to the effect of the binder, was less affected by the decrease in the fiber volume fraction than that of the neat fabric preform.  
Figure 7 shows the K2/K1 values according to the fiber volume fraction. The K2/K1 value is a factor that can be obtained by dividing the permeability in the \(0^{\circ}\) direction (having a minimum flow velocity) of K2 into the permeability in the \(90^{\circ}\) direction (having a maximum flow velocity) of K1. As the shape of flow front of the resin is closer to circular, or isotropic, the factor approaches 1. The fabric preform exhibited a K2/K1 ratio of between 0.7 and 0.82.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Fiber** \\ **Volume** \\ **Fraction (\%)** \\ \end{tabular} } & \multicolumn{6}{c}{**Permeability–K1,K2 (m2)**} \\ \cline{2-7}  & \multicolumn{3}{c}{**Neat Fabric**} & \multicolumn{6}{c}{**Binder (Thermal Treated)**} \\ \cline{2-7}  & \(\mathbf{K_{1}}\) & \(\mathbf{K_{2}}\) & \(\mathbf{K_{2}/K_{1}}\) & \(\mathbf{K_{1}}\) & \(\mathbf{K_{2}}\) & \(\mathbf{K_{2}/K_{1}}\) \\ \hline
**55** & \(7.29\times 10^{-11}\) & \(5.97\times 10^{-11}\) & \(8.19\times 10^{-1}\) & \(1.45\times 10^{-11}\) & \(1.06\times 10^{-11}\) & \(7.31\times 10^{-1}\) \\ \hline
**60** & \(6.16\times 10^{-11}\) & \(4.30\times 10^{-11}\) & \(6.98\times 10^{-1}\) & \(1.27\times 10^{-11}\) & \(9.93\times 10^{-12}\) & \(7.82\times 10^{-1}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: The permeability of the fabric preform in the in-plane direction.  
Figure 6: Change in the permeability in the in-plane direction according to the binder treatment.