## 2 Ballistic Impact Test
### Testing Methods  
The actual projectile impact velocity was measured by a velocimetry system installed between the gun muzzle and the target because it runs independently and has high accuracy. As a projectile passes through the velocimetry system, successive laser beams are obstructed, generating corresponding voltage signals. Given the time interval between two trigger signals and the distance between laser beams in the velocimeter, the velocity is determined. In the actual process, fragments such as foam in the sabot may interfere with the measurement of the velocimeter, so the speed of each test was checked by high-speed photography. Furthermore, the muzzle is very close to the target to reduce the flight distance of the projectile, thereby reducing the speed change and attitude change during the flight of the projectile, so as to improve the test accuracy.  
Figure 4 shows how the specimens were mounted. Unlike the usual axisymmetric projectile, the blade-like projectile is shaped, making it difficult to control its impact posture. In the present research, the projectile was fixed in an aluminum alloy sabot with four V-shaped grooves at the front edge. When the sabot was captured by the sabot separator, a petal-shaped tear forms and dissipates the kinetic energy of the sabot. The triaxial braided composite plate is fixed along both the short edges using four bolts, leaving the upper and lower edges free. A high-speed camera, MEMRECAM HX-7 (NAC cooperation) is fixed through the bracket above the impact plane to take photos at a frame rate of 3000 frames per second. These high-speed photos are designed to image the target during projectile trajectory and deformation. They also serve to estimate the residual velocity of the projectile for the given perforation conditions.  
Considering that the triaxial braided composite casing using in aero-engine could be subjected to different ambient temperatures, varying from as high as 100-150 \({}^{\circ}\)C to as low as \(-\)50 \({}^{\circ}\)C. To figure out the influences of environmental temperature during service, we also conducted a series of impact tests of a 2D triaxial braided composite target plate at high temperature (150 \({}^{\circ}\)C) and cryogenic temperature (\(-\)50 \({}^{\circ}\)C). For the high-temperature tests, the composite target was heated at 2 \({}^{\circ}\)C/min to a predetermined temperature (155 \({}^{\circ}\)C) in an electric blast oven, following which the target was thermally insulat  
Figure 4: Mounting of specimen under test.  
Figure 3: Schematic diagram of ballistic-impact testing device with gas gun system.  
allow the homogenization of the internal temperature of the composite target. The heated target was removed from the insulation and immediately installed in the target holder. For the tests at cryogenic temperature, the target was cooled in a low-temperature chamber filled with dry ice (a solid form of carbon dioxide with a sublimation point of \(-\)78.5 \({}^{\circ}\)C). Dry ice sublimates at normal temperature and pressure, absorbing a large amount of heat from the environment and thereby decreasing the surrounding temperature. The composite target was placed in the cryogenic chamber for 2-3 h and then immediately installed in the target holder. When installing, the bolts are installed with a constant torque wrench with a constant value. Compared with directly on the target plate clamping system, the design of this heating and cooling method could make the clamping pressure of the target plate not change at room temperature, high temperature, and low temperature, thereby exert no interfere with the results. The actual temperature of the target was measured using an infrared thermometer. For both high- and low-temperature tests, the projectile was launched immediately after installing the target in the target holder, and the high-speed camera was triggered to capture images.