A review of research on ballistic impact resistance of bulletproof materials

         There are various classification methods for the impact process. The impact phenomenon can be divided according to the softness and hardness of the projectile (or whether it can be deformed), the thickness of the target plate (semi-infinite target, thick target, medium-thick target, thin target) and speed. Whether the projectile is deformed, the thickness of the target plate and the speed are relative and related to the specific impact process.

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        Most of the literature divides the impact process into low-speed, high-speed and ultra-high-speed impact based on impact speed. In the low speed range (projectile speed less than 250m/s), many problems belong to structural dynamics problems. Local dents or penetrations are closely related to the total deformation of the structure. Typical loading and response times are on the order of milliseconds. As the collision speed increases (0.5-2km/s), for materials within a small range of the collision zone (2-3 times the projectile diameter is the most typical), it is determined by the constitutive equation of the material/structure Structural response becomes secondary, while local responses controlled by inertial effects (stress waves lead to uneven stress distribution in the structure) and strain rate effects (changes in loading rate lead to changes in material properties) become important.

       At this time, it is appropriate to use the wave theory to describe the impact of velocity, geometry, strain rate, local plastic flow and fracture at different stages of the collision. Its typical loading and response times are at the subtle level. High-speed impacts sometimes It's called ballistic impact. The result of further increasing the collision speed (2-3 km/s) is that the local pressure exceeds the material strength by more than an order of magnitude. At this time, the colliding solids can be regarded as compressible fluids in the initial stage of collision. At extremely high ultra-high speeds (greater than 12km/s), the rate of energy deposition is high enough to cause explosive evaporation of colliding materials and a phase change. Under ultra-high-speed collision conditions, the inertial effect of the material and even the compressibility effect or phase change effect will play an important role. The division of speed is not absolute. The difference between low speed, high speed and ultra-high speed is more important because of the different physical phenomena that occur during collision. Obviously, whether it is high speed or low speed has nothing to do with the thickness of the target plate.