# Study on Bulge State of PCnNi3 MoV Target Plates Penetrated by Square Fragments
## 2 Fragment Penetration Test  
Aiming at the problem of prefabricated fragments penetrating flat target plates made of PCrNi3 MoV gun steel, square prefabricated tungsten alloy fragments used in projectiles were used in this study to study the penetration performances of prefabricated fragments at different muzzle velocities. The composition of the gun steel is shown in Table 1.  
The tests were carried out using a 14.5-mm ballistic gun. The layout of the test is shown in Figure 1. The equipment used in the test included a 14.5-mm ballistic gun, gun mount, guard plate, target plate, target frame, and high-speed camera. The tungsten alloy fragments were first put into the sabot, and the muzzle velocities of the fragments were adjusted by the amount of propellant. The maximum fragment velocity could reach 1000 m/s. After the fragments exited the muzzle, they were separated from the sabot to impact the target plate through a hole in the protective plate, while the sabot was intercepted by the protective plate. The penetration characteristics of the tungsten alloy fragments on PCrNi3 MoV steel target plates with different thicknesses in the normal direction were studied. The main parameters of tungsten spherical fragments and the steel target are shown in Table 2.  
Ballistic performance tests of gun steel targets with different thicknesses were then carried out using square fragments with side lengths of 6-mm. In order to measure the bulge height of the target plate, the penetrated parts of the target were cut, and the axial displacement of the center point of the impact surface of the target plate, i.e., the maximum deformation was used as the bulge height \(h_{g}\), as shown in Figure 2. When the target plate was not perforated, the larger the bulge height was, the greater the damage was. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**C** & **Si** & **Mn** & **Cr** & **P** & **S** & **Mo** & **Ni** & **V** \\ \hline
0.39 & 0.32 & 0.5 & 1.10 & 0.025 & 0.020 & 0.28 & 1.80 & 0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of PCrNi3 MoV (%). Figure 1: Setup of the ballistic impact test. The impact damage modes of the gun steel target plate were studied, which included cratering, compression, shearing, and tension. Figure 3 shows the 6-mm target plate impacted by the fragment at different striking velocities. From the top view, when the fragment velocity was 277 m/s, the penetration depth was shallow, and the fragment left a small square pit on target plate. Moreover, due to the reverse force of the target plate, the fragment bounced back. As the fragment velocity increased, the degree of damage to the target plate gradually increased, as indicated by the size and depth of the pit in the frontal view and the bulge height in the side view. When the muzzle velocity of the fragment was less than the ultimate penetration velocity and the fragment embedded in the target plate to a certain depth, it left a rectangular hole in the plate, and the higher the velocity of the fragment, the deeper the hole. From the side view of the cut target plate, as the velocity of the fragment increased, the bulge height of the target plate increased. When the fragment velocity reached 658 m/s, the target plate was sheared and blocked, at which point, the ultimate penetration velocity was reached. The comparison of the pit depth and the bulge height showed that the pit depth was larger than the bulge height, and the greater the penetration kinetic energy, the larger the difference. This was because, in addition to tensile failure, the target plate was also subjected to compressive failure. Tensile failure caused a bulging phenomenon on the back of the target plate, and the compressive failure caused the pit depth to be larger than the bulge height. To illustrate the impact damage modes, the microstructure of the gun steel target plate impacted by the fragment at different striking velocities was characterized by using scanning electron microscopy (SEM).