## 3 Results and Discussion  
### Influence of Projectile Material  
Table 1 shows the results of high-speed impact tests on 2D triaxial braided composites using different types of projectiles at room temperature (20 \({}^{\circ}\)C). In the impact analysis, the ballistic performance is normally measured by energy absorption. Energy absorption of composites is defined as the consumption of kinetic energy of the projectile. For cases that projectiles rebound, it is considered as the total kinetic energy of the projectile is absorbed by fabric targets. According to the initial velocity and residual velocity, the energy absorption of fabrics can be calculated as:  
\[E_{absorbed}=\left\{ \begin{array}{ll}\frac{1}{2}mV_{i}^{2}&(\text{Rebound} )\\ \frac{1}{2}m(V_{i}^{2}-V_{r}^{2})&(\text{Perforation})\end{array} \right. \tag{1}\]  
in which \(m\) denotes the projectile mass, \(V_{i}\) denotes the initial velocity of the projectile, and \(V_{r}\) denotes the residual velocity of the projectile. Two sets of impact tests were performed with cylindrical gelatin projectiles: one with a projectile velocity of 169 m/s and another with a projectile velocity of 213 m/s. However, even with an impact velocity as high as 213 m/s, the triaxial braided composites were not perforated by the gelatin projectile. On the contrary, the gelatin projectile flows and fragments during impact. We thus deduce that the ballistic-limit velocity is greater than 213 m/s. As the gelatin projectile flow away after impact, the residual velocity could not be obtained, therefore the energy absorption is not available. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Testing** & **Projectile** & **Impact Velocity \(V_{1}\)** & **Residual** & **Testing** & **Energy** & **Average** & **Standard** \\
**Number** & **Weight \(m\) (g)** & **(m/s)** & **Velocity \(V_{r}\) (m/s)** & **Results** & **Absorption** & **Energy** (J)** & **Absorption (J)** \\ \hline \hline \multirow{2}{*}{Gelatin-1} & \multirow{2}{*}{25.6} & \multirow{2}{*}{169} & \multirow{2}{*}{–} & Projectile & \multirow{2}{*}{365.58} & \multirow{2}{*}{–} & \multirow{2}{*}{–} \\  & & & & & & & \\ \multirow{2}{*}{Gelatin-2} & \multirow{2}{*}{27} & \multirow{2}{*}{213} & \multirow{2}{*}{–} & Projectile & \multirow{2}{*}{612.48} & & \\  & & & & & & & \\ \hline \hline \multicolumn{1}{c}{Ti-1} & \multirow{2}{*}{25} & \multirow{2}{*}{105} & \multirow{2}{*}{23} & \multirow{2}{*}{Perforation} & \multirow{2}{*}{131.2} & \multirow{2}{*}{150.4} & \multirow{2}{*}{22.58} \\ \multicolumn{1}{c}{Ti-2} & \multirow{2}{*}{24.3} & \multirow{2}{*}{146} & \multirow{2}{*}{83} & \multirow{2}{*}{Perforation} & \multirow{2}{*}{175.29} & \multirow{2}{*}{150.4} & \multirow{2}{*}{22.58} \\ \multicolumn{1}{c}{Ti-3} & \multirow{2}{*}{24.8} & \multirow{2}{*}{160} & \multirow{2}{*}{118} & \multirow{2}{*}{Perforation} & \multirow{2}{*}{144.78} & & \\ \hline \hline \multicolumn{1}{c}{CFRP1} & \multirow{2}{*}{27.8} & \multirow{2}{*}{118} & \multirow{2}{*}{0} & \multirow{2}{*}{Rebound} & \multirow{2}{*}{193.54} & \multirow{2}{*}{} & \multirow{2}{*}{} \\ \multicolumn{1}{c}{CFRP2} & \multirow{2}{*}{27.3} & \multirow{2}{*}{131} & \multirow{2}{*}{0} & \multirow{2}{*}{Rebound} & \multirow{2}{*}{234.25} & \multirow{2}{*}{267.1} & \multirow{2}{*}{24.38} \\ \multicolumn{1}{c}{CFRP3} & \multirow{2}{*}{26.1} & \multirow{2}{*}{157} & \multirow{2}{*}{45} & \multirow{2}{*}{Perforation} & \multirow{2}{*}{255.37} & & \\ \multicolumn{1}{c}{CFRP6} & \multirow{2}{*}{27.1} & \multirow{2}{*}{10} & \multirow{2}{*}{108} & \multirow{2}{*}{Perforation} & \multirow{2}{*}{252.67} & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Results of high-speed impact tests of triaxial braided composites with projectiles made of various materials at room temperature. Three sets of impact tests were carried out using titanium-alloy blade projectiles and impact velocities ranging from 105 to 160 m/s.