## 3 Results and Analysis
### Analysis of Residual Characteristics of Projectile Penetrating into Liquid Cabin at an Attack Angle  
Figure 12 shows the deformation and failure morphology of the projectiles after the penetration tests under various attack angles. Mass abrasion occurs in both radial and axial directions of the projectile (the residual mass increases due to high-temperature fusion of the projectile and front plate fragments in Test 2). Compared with water entry under normal penetration (Figure 4d), the water entry projectile with an attack angle undergoes obvious asymmetric deformation. In the radial direction, one side of the projectile presents overall wavy erosion, whereas the other side shows no deformation; in the axial direction, one side of the projectile undergoes mushrooming deformation, and the other side suffers slight mass loss. Adiabatic shear failure occurs during the high-velocity projectile impact on the target plate, generating a large amount of heat. As the heat is transferred to the projectile, the yield strength of the projectile is reduced, causing mushrooming and erosion to the projectile nose; the sides of the projectile with an attack angle also impacts the front plate, causing \"strip\" erosion. The impacted part of the front plate drives the nearby region to move backward, and the velocity of the plate exceeds that of the projectile. Then, a gap is produced between the projectile and the front plate after the initial impact, and as the projectile moves forward, its side impacts the front plate again, causing \"strip\" erosion to this side again; after multiple impacts, the side shows wavy erosion. After the projectile enters the water, one side and the nose of the projectile are impacted by the water, leading to erosion and mushrooming deformation of the projectile; due to the reduced velocity of the projectile after water entry, its deformation in water is relatively small; cavitation occurs on the other side of the projectile due to its high-velocity motion; the projectile on this side is always in the cavitation region and does not contact with the water; thus, deformation does not occur to this side; when the projectile impacts the rear plate, a small deformation occurs as the velocity at this time has been completely decayed. Figure 11: Trajectory of projectile in Test 3. (The red dash line is the dividing line of different stages). In conclusion, when the initial velocity of the projectile is 1000 m/s, the penetration into the front plate takes the shortest time but is the main stage when projectile failure occurs, featuring a small deformation and mass abrasion of the projectile. The failure morphology of the high-velocity rod projectile is studied by numerical calculation. The specific working conditions are shown in Figure 13.  
As the front plate is thin, the penetration of the high-velocity projectile into liquid is the main stage of projectile failure. As can be seen from Figure 13, the projectile enters the  
Figure 12: The remaining projectile after the tests. (**a**) Remaining projectile in Test 1; (**b**) remaining projectile in Test 2; (**c**) remaining projectile in Test 3; (**d**) remaining projectile under normal penetration [24]. Figure 13: Projectile failure morphology under different working conditions (**a**) No. 19 erosion-mushrooming; (**b**) no. 20 overall plastic bending; (**c**) no. 21 overall plastic bending; (**d**) no. 22 side erosion; (**e**) no. 23 side erosion (**f**) no. 29 erosion—mushrooming; (**g**) no. 30 fracture; (**g**) no. 31 fracture; (**i**) no. 32 overall plastic bending; (**j**) no. 33 side erosion; (**k**) no. 34 bending. water at a high velocity, which causes great deformation of the projectile.