Bulletproof Alumina Ceramics | Uncover the secrets of bulletproof armor ceramic materials
With the gradual upgrading of projectile materials and properties, armor materials are facing great challenges. Facing the increasingly threatening “spear”, we must cast an indestructible “shield” to improve military protection performance and security level. This demand promotes the accelerated development and wide application of composite armor, and one of the important materials is high-performance bulletproof ceramic materials. What is the bulletproof principle of ceramic materials? The basic principle of armor protection is to consume projectile energy, slow down the projectile and achieve harmlessness. Most traditional engineering materials, such as metal materials, absorb energy through structural plastic deformation, while ceramic materials absorb energy through micro crushing process. The energy absorption process of armor ceramics can be roughly divided into three stages. (1) Initial impact stage: the projectile impacts the ceramic surface to blunt the warhead and absorb energy in the process of crushing the ceramic surface to form a small and hard fragment area; (2) Erosion stage: the blunt projectile continues to erode the fragment area to form a continuous ceramic fragment layer; (3) Deformation, crack and fracture stage: finally, tensile stress is generated in the ceramic to break the ceramic, and then the back plate is deformed, and the remaining energy is absorbed by the deformation of the back plate material. In the process of projectile impacting ceramic, both projectile and ceramic are damaged. What are the requirements of armor ceramics for material properties? Because of the brittleness of ceramic itself, it breaks rather than plastic deformation when impacted by projectile. Under tensile load, fracture first occurs in heterogeneous places, such as pores and grain boundaries. Therefore, in order to minimize the micro stress concentration, armor ceramics should be high-quality ceramics with low porosity (up to 99% of the theoretical density) and fine grain structure.
Material properties and their influence on bulletproof performance. According to the data, the mechanical properties of bulletproof ceramics should be: elastic modulus E ≤ 280gn / M < sup > 2 < / sup >, hardness HV ≥ 2000, density ρ ≤ 3000kg / M < sup > 3 < / sup >, the high elastic modulus of ceramics can deform and compress the warhead during impact, and the high hardness ensures that the warhead is ploughed and crushed and absorbs its energy when the warhead penetrates the ceramic plate. Numerical simulation shows that among the five parameters of ceramic shear modulus, elastic limit, tensile strength, compressive strength and damage resistance, the armor piercing protection coefficient of alumina ceramic is the most sensitive to the shear modulus. Improving the ceramic shear modulus is expected to be the most effective way to improve the protection performance of alumina based bulletproof ceramics.
Size effect of ceramics
The bulletproof ceramics used in composite armor can be cylindrical, square and hexagonal. Among them, cylindrical ceramics have the best bulletproof ability, but there are large gaps; Square ceramic blocks have many straight seams with poor bulletproof performance, which affects their bulletproof performance; Hexagonal ceramics have good comprehensive properties, but the shape and size of ceramic blocks are required to be accurate.
Restraint method of ceramic
When bulletproof ceramics are penetrated by projectiles, only when their volume integrity and non expansion are maintained, can they give full play to the various energy dissipation mechanisms of ceramic high anti elastic energy. The results show that under good constraints, the penetration resistance of ceramics is much better than that of unconstrained ceramics. four
What are the ceramic materials used for armor protection
Ceramic materials used for armor protection mainly include alumina, boron carbide and silicon carbide.
- As an ionic bonding compound, alumina ceramics have strong chemical bonding force, high melting point (2050 ℃), good oxidation resistance and chemical inertia. Sintered products have smooth surface, stable size and low price. Therefore, they are widely used in all kinds of armored vehicles and military and police bulletproof clothing. However, the high density, low hardness and fracture toughness of Al2O3 make its bulletproof performance relatively low.
- Boron carbide is a strong covalent bond compound with covalent bond up to 93.9%. It has high melting point and extraordinary hardness (35 ~ 45gpa), which is second only to diamond and cubic boron nitride. In particular, its nearly constant high-temperature hardness and good mechanical properties make B4C one of the high-temperature wear-resistant materials with great development potential. B4C has the lowest density among several commonly used armor ceramics, and its high elastic modulus makes it a good choice for military armor and space materials. The main problems of B4C are its high price (about 10 times that of alumina) and high brittleness, which limit its wide application as single-phase protective armor.
- Silicon carbide has extremely strong covalent bond and still has high strength bonding at high temperature. This structural feature gives silicon carbide ceramics excellent strength, high hardness, wear resistance, corrosion resistance, high thermal conductivity and good thermal shock resistance; At the same time, silicon carbide ceramics have moderate price and high cost performance. It is one of the most potential high-performance armor protective materials.
Ceramic properties suitable for making armor
Preparation technology and material technology trend of typical bulletproof ceramics
From the characteristics of ceramic material preparation process, it can be seen that at present, the more mature processes are reaction sintering, pressureless sintering and liquid phase sintering. These three sintering methods have low production cost, simple preparation process and high possibility of mass production. Hot pressing sintering and hot isostatic pressing sintering are relatively limited by product size, with high production cost and low maturity. In general, ultra-high pressure sintering, microwave sintering, discharge plasma sintering and plasma beam melting have the lowest maturity. They are relatively novel preparation methods. However, they have high requirements for technology and equipment, high production cost and low feasibility of realizing batch. They are often used in the experimental exploration stage.
With the development demand of lightweight and efficient armor system, the advantages of bulletproof ceramics are becoming more and more prominent. From single-phase ceramics, multiphase ceramics to fiber composite ceramics, the fracture toughness of the materials is gradually improved, and the ability to resist multiple blows is constantly upgraded. With the development of material preparation technology, new materials with higher performance are continuously developed and studied. Nano materials and layered structures provide many new choices for material designers to create more exotic composites to minimize the expansion of impact failure. Carbon nanotubes show high strength and stiffness, and inorganic fullerenes have great potential in energy absorption. In addition to the development of materials, the design of new composite armor is also another research hotspot.
What are the technical ways to improve the properties of bulletproof ceramics
At present, the main ways to improve the performance of bulletproof ceramics for protective armor are as follows:
Fiber toughening and strengthening The strain of SiC fiber / SiC composite ceramics can be increased by 9 times than that of pure SiC ceramics; The fracture toughness of Si3N4 with continuous carbon fiber is more than 4 times higher than that of pure Si3N4. In addition, the newly developed plastic ceramics have better bulletproof performance than pure ceramics, and can withstand the continuous penetration of multiple projectiles.
Functionally gradient materials
The composite ceramic material with continuous change from ceramic to metal is prepared by special process method, which has better bulletproof performance than the composite armor composed of ceramic plate and metal plate.
Ceramic surface treatment
In order to effectively improve the crack resistance of ceramics, mechanochemical polishing, surface micro oxidation, vapor deposition and laser surface treatment can be used to improve the surface state of ceramics. In addition, implantation of metal ions on the surface of alumina ceramics by ion implantation can increase the surface hardness by about 50%; The bending strength of silicon carbide and silicon nitride can be increased by 20% ~ 30%.
Development status of global bulletproof armor ceramic materials
Ceramic bulletproof armor has become a rapidly growing industry in the world due to the war on terrorism. Whether it is human body protection or vehicle armor protection, advanced ceramics have many advantages over conventional materials, mainly including light weight, high hardness, unified control of microstructure, so they can resist more serious threats.
Ceramic bulletproof vest
Among the main bulletproof ceramic materials such as boron carbide (B4C), silicon carbide (SIC), alumina (Al2O3) and other high hardness ceramic materials, silicon carbide ceramics have become the mainstream products of international bulletproof ceramics in recent years, including human body bulletproof vest, helicopter belly bulletproof layer, tank armored vehicle bulletproofblayer, etc. because of their high hardness, good bulletproof effect and far lower manufacturing cost than boron carbide ceramics with better bulletproof performance. For example, Ceradyne provides more than $1 billion in bulletproof ceramic armor to the U.S. military every year.
Properties of SiC bulletproof ceramic materials produced by internationally renowned companieszjwelahead.com More about bulletproof Bulletproof Alumina Ceramics