Bulletproof jackets are used to protect the body from harm caused by bullets or fragments. Bulletproof jackets mainly consist of two parts: a clothing cover and a bulletproof layer. The clothing cover is usually made of synthetic fabrics, while the bulletproof layer is made of materials such as metal (special steel, aluminum alloy, titanium alloy), ceramic pieces (corundum, boron carbide, silicon carbide, alumina), Fiberglass, nylon, kevlar, ultra-high molecular weight polyethylene fiber, liquid protective materials, polyimide fibers, and other materials, which can be combined to form a single or composite protective structure.
Whether a bulletproof vest can resist a knife mainly depends on the material and purpose of the vest. Bulletproof jackets with steel plates and ceramic armor plates can resist not only knife cuts but also stabs, while ordinary fiber bulletproof jackets, namely Kevlar bulletproof jackets, are not very effective against knife stabs. The reason why fiber bulletproof jackets cannot effectively resist knives is that fibers have some gaps, and the sharp parts of knives can puncture the gaps in the fibers, and then expand the gaps of the fibers continuously, finally penetrating the bulletproof jacket and entering the body. In actual use, police officers wearing fiber bulletproof jackets also wear anti-stab vests outside, which can achieve the effect of anti-stabbing.
The bulletproof principle of fiber bulletproof jackets is to consume the energy of the bullet, reduce the penetration of the bullet, and cause the deformation of the bullet. This bulletproof principle requires the bullet to come at a very fast speed, and the shock wave produced by the impact is absorbed and dispersed by the fiber. At this time, the bullet will also be suppressed and deformed by the shock wave, and then lose its penetrating ability. This bulletproof principle has significant benefits for protecting against handgun bullets, rifle bullets, and explosive fragments. However, it is ineffective against snipers and strong-caliber bullets with strong penetrability, which has minimal effect. Meanwhile, bulletproof jackets with plates such as steel or ceramic armor inserts can provide some protection against large-caliber bullets and sharp weapons, so why are they not generally equipped?
Because, in actual combat, steel plate bulletproof jackets are relatively bulky, which is not conducive to the mobility of soldiers and can even cause unnecessary casualties. In contrast, fiber bulletproof jackets hardly affect the mobility of soldiers and are convenient to wear just like a vest, which is why armies of various countries do not generally equip bulletproof jackets with steel plates or ceramic armor plates.