Since the end of the Second World War, advanced ceramics have begun to attract researchers' attention as an armor material. With a series of scientific research personnel corresponding to the exploration of the ceramic materials used for the protection of armor materials, it has become one of the important parts of today's composite armor. This article briefly introduces the ceramic materials in the armor protection materials.
(1) The bulletproof principle of advanced ceramic materials
The basic principle of armor protection is to consume its projectile energy at the same time under the impact of the warhead, and the projectile speed is reduced to achieve the final protection effect. The amount of plastic deformation of advanced ceramic materials is close to 0. Although it is impossible to absorb the energy brought by the warhead through the plastic deformation of its own structure, it can absorb energy through the micro-crushing process when it receives a strong impact from the warhead.
Advanced ceramic materials can absorb energy in three stages:
①Initial impact stage: When a powerful warhead hits the ceramic surface, the hardness of the ceramic is higher than the flight speed of the warhead, so the warhead will be passivated, so that it will be absorbed during the process of crushing the ceramic surface to form small and hard fragments. 40% flight ability.
②Erosion stage: The deformed warhead continues to erode the fragment area with the remaining kinetic energy. When the ceramic fragments generate huge friction with it, the projectile will be further absorbed by about 30% ~ 40% of the flying kinetic energy.
③Deformation, cracks and fracture stage: When the ceramic is tensioned, it will cause it to rupture, and the back plate will also be deformed. The remaining flying kinetic energy of the projectile will be absorbed by the deformed back plate material as a whole to achieve the role of protection.
The absorption capacity of ceramics is related to its hardness and elastic modulus. The higher the hardness, the easier the projectiles to passivate or shatter when the projectile hits the ceramic, and the more the projectile consumes the ability to erode the ceramic.
(2) Performance comparison of ceramic materials for protective armor
Bulletproof ceramics have strict requirements on their performance requirements, including but not limited to: density, hardness, elastic modulus, strength, fracture toughness, fracture mode, microstructure, etc.
There are many types of advanced ceramic materials. Typical bulletproof ceramic materials mainly include alumina, boron carbide, silicon carbide, silicon nitride, etc.
Alumina (Al2O3) has the highest density, strong chemical bonding force, high melting point, good oxidation resistance and chemical inertness, and the price is relatively cheap. It is mostly used in various armored vehicles, military and police protective clothing and other appliances. The disadvantage is that the high density, low hardness and fracture toughness make it less elastic.
Boron carbide (B4C) has the lowest density, highest hardness, extremely strong covalent bonds, high melting point, high elastic modulus, and good mechanical properties. It is mostly used in advanced military armor and space. The disadvantage is that it is expensive and brittle, which limits the expansion of the application field of boron carbide.
Silicon carbide (SiC) has extremely strong covalent bonds, high strength, high thermal conductivity, corrosion resistance, wear resistance, good thermal shock resistance, high cost performance, and wide application fields.
(3) Fiber-reinforced ceramic composites
The equipment of military personnel has high requirements for the protection of light structures, in order to achieve the purpose of rapid movement. Fiber composite ceramic materials provide a good combination of energy absorption and mass reduction to a large extent. The fibers used for toughening ceramics mainly include glass fiber and carbon fiber, which can greatly increase the fracture strain and elastic modulus of the material. Compared with glass fiber, carbon fiber has better advantages: because it is fired from raw fiber at high temperature, it has undergone low temperature oxidation, medium temperature carbonization, high temperature graphitization, etc., so its strength, modulus, thermal conductivity is higher, and density is low. It has the advantages of small linear expansion coefficient and high temperature resistance. It is a good reinforcement and toughening ceramic material. Carbon fiber toughened composite materials can minimize the volume effect of ceramic defects, and play the role of fiber toughening and reinforcement to improve the anti-ballistic performance of ceramic composite materials.