New materials and technologies for armor protection

Although we are in peace now, the confrontation of modern warfare is relatively fierce. The omni-directional, three-dimensional, high-density fragment attacks formed by the explosion of high-performance weapons such as long-range attacks, battlefield stray bullets, and preset fragments have caused serious vehicle damage and personnel Casualties. In order to adapt to the transformation of modern warfare, the protection level of military vehicles is becoming higher and higher.

Performance and application of armor protection materials

Armor protection materials for equipment at home and abroad mainly include bulletproof glass, bulletproof steel plate, bulletproof ceramics, bulletproof high-strength glass fiber, bulletproof aramid fiber, bulletproof PE fiber, etc.

1. Bulletproof glass

  At present, bulletproof glass is mainly composed of inorganic glass and organic materials, which mainly include the following:

(1) Interlayer composite of float glass and PVB interlayer film.

In this method, the multi-layer float glass is bonded with a polyvinyl butyral interlayer film and subjected to high temperature and high pressure treatment to make them compound together to form a transparent whole, forming a glass with bulletproof ability. The advantages of this bulletproof glass are The optical performance is considerable, and it shows good impact resistance. At the same time, it has good environmental stability, not easy to aging, long life, low cost, and easy maintenance; the disadvantage is that it is large in size and suitable for installation in fixed places.

(2) Laminated glass and organic transparent board are superimposed or composited.

This kind of bulletproof glass has two forms, one is to place a layer of organic transparent board behind a layer of laminated glass, and the laminated glass is placed in front of the organic transparent board as an impact layer. This is a superposition method. The other is glass and Polycarbonate board and (PC board) are directly compounded into bulletproof glass, and the bonding material is polyurethane film (PU film). The production process is similar to the PVB sandwich method. The above two methods use more organic materials, Compared with PVB glass, it has the following characteristics:

First, the volume and mass are small, and the bulletproof ability is strong in the case of the same thickness or the same mass;

Second, this kind of bulletproof glass will not produce splashes as long as it is not penetrated by bullets when it is shot;

Third, the rigidity of organic materials is far less than that of glass. Because the coefficient of thermal expansion of organic materials is different from that of glass, it is easy to deform, and the optical properties are not easy to control; fourth, organic materials are easily aging when exposed to the atmosphere, and the surface hardness of the materials is low. It is easily scratched, so the service life is short. In addition, the cost of this bulletproof glass is relatively high, and it is generally used on vehicles, ships, and aircraft.

Military vehicles should choose bulletproof and riot glass composed of laminated glass and organic transparent board.It is made of high-quality safety glass and imported high-strength PC board (polycarbonate with an impact strength of 250 times that of glass) through PVB film (polyethylene The butyral interlayer film) is made by high-pressure polymerization. The quality is only 65% of ordinary bulletproof glass, and it has strong impact resistance, flame retardancy, good light transmission and no spatter. This kind of bulletproof glass Moderate price, easy to be adopted by general users, long service life, can coexist with buildings or vehicles for a long time.

2. Bulletproof steel plate

 Bulletproof vehicle

Metal bulletproof materials (including bulletproof steel, aluminum alloy, titanium alloy, etc.) have been widely used in military (tanks, armored vehicles, etc.) and civilian protection (currency transport vehicles, armed police, public security explosion-proof vehicles and bulletproof cars) from the past to the present, and With the increasing requirements of weapons and ammunition for the anti-penetration ability, impact resistance and collapse resistance of armor protection materials, metal ballistic materials have developed from ordinary steel armor to high-hardness steel armor, dual-hardness steel composite armor, and even titanium alloy armor. The armor steel material is mainly Cr2Ni2Mo alloy series armor steel, which changes the hardness of the armor steel plate by adjusting the carbon content, and classifies the armor steel plate by the hardness value HRC50. The hardness of 24C, 28C, and 30C is less than or equal to HRC50. It belongs to high-hardness armor steel; 39C and 44C have a hardness greater than HRC50 and belong to ultra-high-hardness armor steel.

With the increase of carbon content, the strength and hardness of armored steel plates increase, and plasticity and toughness decrease. There are two types of bulletproof plates used for anti-light machine guns: one is hot-rolled plates, with SSAB's DomexProtect (Defend) 250 and 300 is the representative. The tensile strength of this kind of steel plate is 900~1000MPa, the comprehensive performance is good, the thickness of the plate is 3.0~3.2mm, and its cold workability, cold bending performance (d=2a 180℃ without cracking), weldability and other properties are good The other type is heat-treated steel plate, which is to improve the strength of the hot-rolled plate by quenching and tempering heat treatment to meet its bulletproof requirements. Sweden's DomexProtect (Defend) 500 is one of its typical grades. Its tensile strength is greater than 1500MPa, When used for anti-light submachine guns, its thickness can be reduced to 2.4~2.6mm; when anti-56 submachine guns, its thickness is 4.5mm. The cold bending radius must be greater than 18mm, and it also has good weldability. This type of steel is a microalloy C-Mn steel. The above properties are obtained through controlled rolling or heat treatment. During smelting, the content of P, S and O is reduced as much as possible, and inclusions are reduced to maintain the workability of the steel.

Traditional metal armor materials such as steel plates have high density, and weapons with high lethality and explosive power require that the armor must reach a certain thickness, and the use of thick and heavy steel plate armor must sacrifice its payload for vehicles, ships, and aircraft. The heavy armor material makes it difficult to manipulate, reduces flexibility and increases the failure rate of the engine.

3. Bulletproof ceramics

  Bulletproof ceramic tank

In 1918, it was discovered that covering a thin and hard enamel on the metal surface can improve its elastic resistance, so this technology was used in tanks during World War I. After the 1960s, A12O3 ceramic panel armor was used to adhere to aluminum or glass fiber reinforced plastic backing The composite protective armor was formed to prevent the penetration of high-speed projectiles. Later, ceramic armor materials such as B4C, SiC, and Si3N4 appeared one after another.

Ceramic is a brittle material that is easily broken when impacted. It is usually not made into protective armor alone, but is made into composite armor with metal and other fiber materials; the ceramic used in composite armor is usually changed into ceramic blocks. So that when a piece of ceramic is broken by the projectile, other ceramic pieces are still effective.

Ceramic materials are mainly used in armor systems that deal with medium and large-caliber long-rod armor-piercing projectiles.These ammunitions mainly use ablation and destruction mechanisms.They are also used in bulletproof vests.The combination of ceramics and composite back materials provides the required protection. In engineering applications, ceramic composite armor is widely used in the protective armor of tanks, armored vehicles and other equipment. However, the ceramic material has poor plasticity, low fracture strength, is prone to brittle fracture, and cannot be secondary bulletproof. In addition, its molded size is small, and the production The efficiency is low, and because of its extremely high hardness and brittleness, the secondary molding process is very difficult, especially the molding hole processing is particularly difficult, so the preparation cost is high, and the use limitation is large.

At present, the three major ceramic materials used for bulletproof are alumina (Al2O3), silicon carbide (SiC) and boron carbide (B4C). Alumina is more widely used in bulletproof due to its low cost, but its bulletproof grade is better. Low and high density; boron carbide has better ballistic performance and low density, but its price is more expensive.In the 1960s, it was first used as a material for designing bulletproof vests; silicon carbide ceramic materials have advantages in cost, ballistic performance and The density index is between the two. Therefore, it is possible to become an upgraded product of alumina bulletproof ceramics.

 4. Bulletproof high-strength glass fiber

  Armored protective tank

As early as during World War II, the United States had begun to conduct research on FRP armor and successfully developed fiberglass/polyester armor materials. With the emergence of S-2 high-strength fiberglass, high-performance fiberglass composite materials were used as a relatively inexpensive ballistic armor The material becomes the first generation of composite armor material. Its ballistic resistance can reach more than three times that of steel. The former Soviet Union uses fiberglass composite armor to equip T-72 and T-80 tanks, and its composite armor structure is: steel + steel + glass steel + The five-layer structure of steel + lining. This composite armor can absorb a large amount of energy from kinetic energy bombs. The German Blom-Foss company has also developed a similar series of structures, and has been installed in the German Army and the Danish Army. On the "1A3 main battle tank, its protection capability reaches the level of the "Leopard" 1A4 main battle tank with a welded turret. The U.S. Army Materials and Mechanics Research Center (AMMRC) uses high-strength glass fiber composite materials to manufacture track and wheeled vehicle structural armor For example, the "Bradley" composite armored infantry fighting vehicle of the United States United Defense Corporation uses structural composite materials prepared by the S-2 high-strength glass fiber and polyester resin molding process. FRP is also used in armed helicopters, Composite armor structure materials for transport aircraft and communications helicopters.

High-strength glass fiber was developed by Owens Corning (OC) in the United States in the early stage. It has the advantages of excellent anti-elasticity, noise reduction and low characteristic signal. It can effectively improve the survivability of equipment and rapid response and maneuverability. Its cost-effectiveness is even more important in the field of armor protection. The structural strength of glass fiber composite material itself is also particularly good, and the production process is simple, the cost is low, and it is increasingly used as a structure/function integrated material for armored car bodies. And structural parts. The domestic Nanjing Fiberglass Research Institute Sinoma Technology and other companies have realized the industrial production of high-strength glass fiber, independently developed and large-scale industrial production of HS2 and HS4 series of high-strength glass fibers, of which the performance of HS4 high-strength glass fiber products is close to or It has reached American S-2 glass fiber, and its products are SW220 and SW360 satin high-strength glass fiber cloth.

5. Bulletproof aramid fiber

 Armored protective tank

The United States first made aramid composite materials into bulletproof helmets and body armors, and then composited aramid fiber laminates with ceramics or steel plates for tank armor. For example, the US MI main battle tank used a "steel + Kevlar + steel" composite Armor, it can prevent neutron bombs and anti-tank missiles with a thickness of about 700mm, and it can also reduce the instantaneous pressure effect formed in the cockpit due to being hit by the armor-piercing projectile. The key part of the internal structure of the American M113 armored personnel transport vehicle It is also equipped with a Kevlar lining, which can provide after-effect armor protection against the impact and penetration of armor-piercing projectiles, armor-piercing projectiles and anti-personnel projectiles. The U.S. V22Osprey military aircraft and military helicopters are composed of bulletproof composite back plates and ceramic panels. Composite armor is an ideal lightweight armor for helicopters.

6. Bulletproof PE fiber

 Armor protection

UHMWPE fiber was industrially produced by the Dutch DSM company in the 1970s. It is another high-performance fiber developed after aramid, which belongs to the third generation of bulletproof fiber. Its major feature is low density, only 0.97g/ cm3, which is 2/3 of aramid, 1/3 of aluminum and 1/8 of steel, is the lighter one of the developed high-performance fibers. Its specific strength is 35% higher than that of aramid, and because the fiber has The higher modulus under conventional quasi-static conditions can cause high sound velocity propagation, which makes it better than other fibers in energy absorption and stress wave transmission when protecting against bullet impact. UHMWPE fiber is currently recognized as a fiber with relatively good ballistic performance . Ultra-high molecular weight polyethylene fiber composite materials (the Dutch and American trade names are Dyneema and Spectra, respectively) are high-performance fibers with excellent comprehensive properties, which are characterized by high strength, high modulus, low elongation and lighter than water It has low density, excellent corrosion resistance, UV resistance, cutting resistance, and abrasion resistance. It has low moisture absorption and is not affected by the environment. In addition, its high hydrogen atom content makes it excellent in anti-neutron and anti-radiation properties. Dyneema's bulletproof panels are mainly used as vital parts of vehicles, tanks, airplanes, helicopters and ships.