## 3 Results and Analysis
### Analysis of Failure Modes of Liquid Cabin  
Figure 18 presents the deformation morphology and failure diagrams and scanned contours of the front and rear plates before and after the tests. As illustrated, the front plate of the water tank undergoes shear plugging failure and thin film bulging deformation during the projectile penetration into the water tank at a high velocity. When the high-velocity projectile impacts the steel plate at an attack angle with water medium as the \"dynamic support\", the support of water improves the rigidity of the steel plate. As the front plate is thin, the impact on the target plate by the high-velocity projectile causes adiabatic shearing. The light blue color at the edge of the perforation hole is caused by the release of a large amount of heat during the contact between the projectile and the target. Because projectile penetration is at an attack angle, the shape of the hole is not circular, similar to the shape of the projectile nose, but rectangular, similar to the shape of the side of the projectile. The initial shock wave is generated after the projectile impacts the water and enters it. As the shock wave is close to the front plate, it bulges outward after being impacted. Then, due to the long cavitation, the water in the tank moves around and squeeze  
the front plate, leading to the wide bulging deformation of the front plate. However, when [PERSON] conducted the penetration test with the water tank, the front plate was depressed, which was caused by the negative pressure induced by bubble contraction on the front plate due to the closure of the tank. In the present paper, as the tank is not covered, there is no plate depression. Comparing the plate deflection, we see that the kinetic energy of the projectile increases, but the deflection of the front plate does not increase apparently. This is explained by the fact that the front plate mainly undergoes thin film bulging deformation caused by the cavitation load, and the specific impulse of the cavitation load in the three groups of tests is basically the same. Due to the large thickness and stiffness of the rear plate, it has no obvious thin film bulging deformation. Since the projectiles used in Tests 1 and 3 have different masses and L/D ratios, under the same initial velocity, their kinetic energy varies, leading to very different failure modes of the rear plate. In Test 1, the rear plate mainly undergoes bulging and dishing deformation. Due to the long water domain, the incident shock wave generated after the water entry of the projectile is weakened to some extent when reaching the rear plate, having a small influence on the rear plate; as the projectile approaches the rear plate during penetration, a high-pressure region is produced at the position around the projectile nose as the projectile squeezes the water, and this high-pressure region acts on the rear plate, causing dishing deformation; then, the projectile impacts the rear plate, causing bulging deformation. After Test 3, the rear plate has annular breaches and radial cracks. The reason is: as the projectile moves in the water with an attack angle, it keeps overturning; it always has a large attack angle and a certain angular velocity upon reaching the rear plate; as the edge of the projectile nose first touches the target, which is similar to the penetration of a sharp-nosed projectile, the rear plate undergoes severe plastic deformation, and then the material is squeezed toward the cratering position by the sharp nose, causing annular breaches and radial cracks at the edge of the breaches; as the penetration continues, more cracks are generated and developed into petaling failure.