Learn more about bulletproof vests
Brief introduction
Bulletproof vests are armor like protective clothing used to reduce bullet damage. They are worn by police and military. The above name is more or less a misnomer because most of these protective clothing have little or no protection against large calibre rifles or rifles, regardless of the type, style, material, or caliber of the rifle cartridge. These vests provide a wide range of protection against pistol ammunition shot from pistols, regardless of type, style, material, and caliber of pistol ammunition. Some types of bulletproof vests have metal extensions (steel or titanium), and additional ceramic or polyethylene sheets can be added to important parts of the body to increase protection. If the bullet hits the stuffing, these shields will effectively protect all pistols and some rifles. These vests became standard in military use as forward in ballistic technology to disable "kevlar-on1y" - the crisat nat0 standard for vests includes titanium backing.
It is used to protect human body from damage caused by warhead or shrapnel. Bulletproof vest is mainly composed of jacket and bulletproof layer. The garment cover is usually made of chemical fiber. The bulletproof layer is made of metal (special steel, aluminum alloy, titanium alloy), ceramics (corundum, boron carbide, silicon carbide), glass fiber reinforced plastic, nylon, Kevlar and other materials to form a single or composite protective structure. The bullet proof layer can absorb the kinetic energy of warhead or fragment, and has obvious protective effect on low-speed warhead or fragment, and can reduce the damage to human chest and abdomen. Bulletproof vests include infantry bulletproof vests, aircrew bulletproof vests and artillery bulletproof vests.
As a kind of protective equipment, the core performance of bulletproof vest is bulletproof. At the same time, as a kind of functional clothing, it should also have certain wearability.
The bulletproof performance of bulletproof vest is mainly reflected in the following three aspects:
(1) Anti pistol and rifle bullets at present, many soft bullet proof vests can resist pistol bullets, but to prevent rifle bullets or bullets with higher energy, ceramic or steel reinforced plates are needed.
(2) The high-speed fragments produced by various explosives such as bombs, mines, shells and grenades are one of the main threats in the battlefield. According to the survey, the order of threat faced by soldiers in a battlefield is: shrapnel, bullet, blast wave and heat. Therefore, the function of bulletproof sheet should be emphasized.
(3) Anti non penetrating damage bullet will produce a great impact force after hitting the target, and the damage produced by the impact force on human body is often fatal. This kind of injury does not show penetration, but can cause internal injury, serious life-threatening. Therefore, preventing non penetrating damage is also an important aspect of bulletproof performance of bulletproof vest.
Wearability
Bullet proof: on the one hand, the wearing performance requirements of the vest refer to that the body armor should be as light and comfortable as possible without affecting the bulletproof ability, and people can still perform various actions flexibly after wearing them. On the other hand, clothing can adjust the microclimate environment of "clothing human body" system. For bulletproof vests, it is hoped that the human body can still maintain the basic heat and moisture exchange state after wearing the bulletproof vest, so as to avoid the accumulation of moisture on the inner surface of the bullet proof vest, which will cause discomfort such as heat and humidity to the human body, and reduce the physical consumption. In addition, due to its special use environment, bulletproof vests should also consider the adaptability with other weapons and equipment.
Development of bulletproof vests
As an important personal protective equipment, bulletproof vest has experienced the transition from metal armor plate to non-metallic composite material, and from simple synthetic material to synthetic material, metal armor plate and ceramics
The development process of composite system such as shield. The prototype of human body armor can be traced back to ancient times. In order to prevent the body from being hurt, the primitive people used the natural fiber braided belt as the chest protection material. With the development of weapons, human body armor must be improved accordingly. As early as the late 19th century, the silk used in the armor of the Middle Ages in Japan was also used in bulletproof vests made in the United States. After the assassination of President William McConnell in 1901, the bulletproof vest attracted the attention of the United States Congress. Although the bullet proof vest can resist low-speed pistol bullets (the bullet speed is 122 M / s), it cannot prevent rifle bullets. Thus, in the first World War, there appeared bulletproof vests made of natural fiber fabric and steel plate. Thick silk garments were once a major part of bulletproof vests. However, silk deteriorates rapidly in the trench. This defect, coupled with the limited bulletproof ability and the high cost of silk, makes the silk bulletproof vest in the During the first World War, the United States failed to popularize its weapons. In World War II, the lethality of shrapnel increased by 80%, and 70% of the wounded died of trunk injuries. The Warring States, especially Britain and the United States, began to spare no effort to develop bulletproof vests. In October 1942, the British army first developed a bullet proof vest composed of three high manganese steel plates. In 1943, 23 kinds of bulletproof vests were produced and officially adopted in the United States. Special steel was the main bulletproof material in this period. In June 1945, the U.S. Army successfully developed a bulletproof vest composed of aluminum alloy and high-strength nylon, and the model was M12 infantry bulletproof vest. Among them, nylon 66 (scientific name: polyamide 66 fiber) is a synthetic fiber invented not long ago. Its breaking strength (GF / D: Keli / Dan) is 5.9-9.5, initial modulus (GF / D) is 21-58, and specific gravity is 1.14 g / (CM) 3. Its strength is almost twice that of cotton fiber. In the Korean War, the US Army was equipped with T52 all nylon bulletproof vest made of 12 layers of bulletproof nylon, while the Marine Corps was equipped with m1951 rigid "duolong" glass fiber reinforced plastic bulletproof vest, which weighs between 2.7 and 3.6 kg. The bulletproof vest made of nylon can provide some protection for soldiers, but it is larger and weighs up to 6kg. In the early 1970s, a kind of ultra-high strength, ultra-high modulus, Kevlar, a high temperature resistant synthetic fiber, was successfully developed by DuPont company of the United States and was soon applied in the bulletproof field. The appearance of this kind of high-performance fiber greatly improves the performance of the soft fabric bulletproof vest, and also improves the comfort of the bullet proof vest to a great extent. The US military took the lead in using Kevlar to make bulletproof vests, and developed two models of light and light. Kevlar fabric is used as the main material and bulletproof nylon cloth as the cover. The light bulletproof vest consists of 6 layers of Kevlar fabric with a medium weight of 3.83 kg. With the commercialization of Kevlar, Kevlar has been widely used in bulletproof vests of various countries due to its excellent comprehensive performance. With the success of Kevlar and the appearance of Twaron and spectra and their application in bulletproof vests, soft bulletproof vests characterized by high-performance textile fibers have gradually become popular. Their application scope is not limited to the military, but gradually extended to the police and political circles. However, for high-speed bullets, especially those fired by rifles, pure soft body armor is still not competent. For this reason, people In order to improve the bulletproof ability of the whole body armor, fiber composite material is used as reinforcing panel or insert board. To sum up, there have been three generations of modern bulletproof vests: the first generation is hard body armor, which mainly uses special steel, aluminum alloy and other metals as bulletproof materials. The characteristics of this kind of bulletproof clothing are as follows: the clothing is heavy, usually about 20 kg. It is not comfortable to wear, and has a certain bulletproof performance, but it is easy to produce secondary fragments. The second generation of body armor is
Soft body armor is usually made of multi-layer Kevlar and other high-performance fiber fabrics. It is light in weight, usually only 2-3kg. It is soft in texture, good in fitness and comfortable in wearing. It has good concealment when wearing inside. It is especially suitable for the daily wear of police, security personnel or politicians. In terms of bulletproof ability, it can prevent bullets from pistols 5 meters away, and will not produce secondary shrapnel, but it will deform greatly after being hit by bullets, which can cause certain non penetrating damage. In addition, it is difficult to resist bullets from rifles or machine guns with general thickness. The third generation bulletproof vest is a kind of compound bulletproof vest. The main development direction of bulletproof vests is to use lightweight ceramic as outer layer and Kevlar as inner layer.
Bulletproof mechanism of bulletproof vest and its influencing factors
There are two basic bulletproof mechanisms of bulletproof vests: one is the fragment bomb formed after the projectile body is broken Second, the kinetic energy of the warhead is dissipated through bulletproof materials. The first bulletproof vests developed by the United States in the 1920s and 1930s were protected by overlapping steel plates attached to strong clothing. This kind of bulletproof vests and later similar hard body bulletproof vests play a bulletproof role by bouncing off the warhead or shrapnel, or breaking the bullet to consume and decompose its energy. The bulletproof mechanism of soft bulletproof clothing with high-performance fiber as the main bulletproof material is the latter, that is, the fabric made of high-strength fiber can "catch" bullets or shrapnel to achieve the purpose of bulletproof. The results show that there are five ways to absorb energy in soft bulletproof vest
(1) Fabric deformation: including the deformation in the incident direction of bullet and the stretching in the area near the incident point Deformation;
(2) Fabric damage: fiber fibrillation, fiber fracture, yarn structure disintegration
And the disintegration of fabric structure;
(3) Heat energy: energy is dissipated by friction in the form of heat energy;
(4) Sound energy: the energy consumed by the sound emitted by a bullet after hitting the bulletproof layer;
(5) Deformation of projectile body. Soft and hard composite bulletproof vests developed to improve bulletproof capability,
Its bulletproof mechanism can be summarized as "both soft and hard". When a bullet hits a bullet proof vest, the first thing to do with it is hard bulletproof material such as steel plate or reinforced ceramic material. In this instant contact process, the bullet and the hard bulletproof material may deform or break, which consumes most of the energy of the bullet. As the liner and the second line of defense, the high-strength fiber fabric absorbs and diffuses the residual energy of the bullet and acts as a buffer, thus reducing the non penetrating damage as much as possible. In the two bulletproof processes, the former plays a major role in energy absorption, greatly reducing the penetration of the projectile, which is the key to bulletproof.
influence factor
The factors that affect the bulletproof effectiveness of bulletproof vests can be determined from the interaction between projectiles (bullets or shrapnel)
And bulletproof materials. As far as the projectile is concerned, its kinetic energy, shape and material are important factors determining its penetration. Ordinary warhead, especially lead core or steel core projectile, will deform after contacting with bulletproof material. In this process, a considerable part of kinetic energy is consumed by the bullet, which effectively reduces the penetration of the bullet, which is an important aspect of the energy absorption mechanism of the bullet. However, the situation is significantly different for the fragments or secondary fragments formed by bullets when bombs and grenades explode. These bullet proof materials are not sharp in shape, especially in the shape of light armor plates. Generally speaking, the velocity of this kind of debris is not high, but it is large and dense. The key to the energy absorption of these fragments by soft body armor is that the fragments cut, stretch and break the yarn of the bulletproof fabric, and make the inner yarn of the fabric and different layers of the fabric
The interaction between them results in the deformation of the fabric as a whole. In these processes, the fragments work externally and consume their own energy. In the above two types of body energy absorption process, a small part of energy is converted into heat energy through friction (fiber / fiber, fiber / bullet), and converted into acoustic energy by impact. In the aspect of bulletproof materials, in order to meet the requirements of bullet proof vests to absorb the kinetic energy of bullets and other projectiles to the greatest extent, bulletproof materials must have the properties of high strength, good toughness and strong energy absorption capacity. At present, the materials used in bulletproof vests, especially soft bulletproof vests, are mainly made of high-performance fibers. These high performance fibers are characterized by high strength and high modulus. Some high-performance fibers, such as carbon fiber or boron fiber, have high strength, but they are not suitable for human body bulletproof clothing because of their poor flexibility, low fracture work, difficulty in textile processing and high price. Specifically speaking, for bulletproof fabric, its bulletproof function mainly depends on the following aspects: tensile strength of fiber, breaking elongation and breaking work of fiber, modulus of fiber, orientation degree and stress wave transmission velocity of fiber, fineness of fiber, aggregation mode of fiber, weight of unit area, structure and surface characteristics of yarn, The fabric structure, the thickness of fabric layer, the number of layers of mesh or fabric layer, etc. The properties of fiber materials used for shock resistance depend on the fracture energy of fibers and the velocity of stress wave transmission. The stress wave should be diffused as soon as possible, and the fracture energy of the fiber under high speed impact should be increased as much as possible. The tensile fracture work of materials is the energy that the material has to resist external force breaking, which is a function related to tensile strength and elongation deformation. Therefore, theoretically, the higher the tensile strength, the stronger the elongation and deformation capacity of the material, the greater the potential of energy absorption. However, in practice, the material used for bulletproof vests is not allowed to have excessive deformation, so the fiber used for the bulletproof vest must have a high resistance to deformation, that is, high modulus. The influence of yarn structure on bulletproof ability is due to the difference of single fiber strength utilization rate and yarn overall elongation deformation ability caused by different yarn fabrics. The process of yarn breaking is first It depends on the fracture process of the fiber, but because it is an aggregate, there are great differences in the fracture mechanism. If the fineness of the fibers is fine, they will be close to each other in the yarn, and the force will be more uniform, so the strength of the yarn will be improved. In addition, the parallelism of fiber arrangement, the transfer times of inner and outer layers, and the twist of yarn have important influence on the mechanical properties of yarn, especially the tensile strength and breaking elongation. In addition, due to the interaction between yarn and yarn and between yarn and projectile, the surface characteristics of yarn will enhance or weaken the above two effects. The existence of oil and moisture on the surface of yarn will reduce the resistance of bullet or fragment penetrating material
Synthetic fibers with high tensile strength and high modulus are usually highly oriented
The surface is smooth and the friction coefficient is low. When these fibers are used in bulletproof fabric, the ability of transmitting energy between fibers is poor, and the stress wave can't spread rapidly, which also reduces the ability of the fabric to resist bullets. The common methods to improve the surface friction coefficient, such as fluffing and corona finishing, will reduce the strength of the fiber. However, the method of fabric coating is easy to cause the "welding" between the fibers. As a result, the bullet shock wave will be reflected in the transverse direction of the yarn and the fiber will break prematurely. In order to understand this contradiction, people have come up with various methods. United signal has introduced to the market an air wound treated fiber, which increases the contact between bullets and fibers by entanglement of fibers inside the yarn. In American patent 5035111, a method for improving yarn friction coefficient by using skin core structural fiber is introduced. The "core" of this kind of fiber is high strength fiber, while the "skin" is a kind of fiber with lower strength and higher friction coefficient, and the proportion of the latter is 5% - 25%. The method invented by another US patent 5255241 is similar to this method, which is to coat a thin layer of high friction coefficient polymer on the surface of high strength fiber to improve the resistance of fabric to metal penetration. This invention emphasizes that there should be a strong adhesion between the polymer and the surface of the high-strength fiber, otherwise the coating material peeled off during the impact will act as a solid lubricant between the fibers, thus reducing the friction coefficient of the fiber surface. In addition to fiber properties and yarn characteristics, the fabric structure is also an important factor affecting the bulletproof ability of bulletproof vests. The fabric structure types used in software bulletproof clothing include knitted fabric, woven fabric, weft free fabric, needle punched nonwoven felt, etc. Knitted fabrics have a high elongation, which is conducive to improving the comfort of wearing. However, this high elongation for impact resistance will produce great non penetrating damage. In addition, due to the anisotropic characteristics of knitted fabrics, it leads to the difference between the It has different degree of impact resistance in the direction. So, despite the knitting fabric in the production cost and production efficiency.
But it can only be used to manufacture stab proof gloves, fencing clothes, etc., but can not be used completely on bulletproof vests. At present, woven fabrics, weft free fabrics and needle punched nonwovens are widely used in bulletproof clothing. Due to their different structures, these three kinds of fabrics have different bulletproof mechanisms, At present, ballistics can not give a full explanation. -Generally speaking, when the bullet hits the fabric, it will produce a radial vibration wave in the impact area and spread through the yarn at high speed. When the vibration wave reaches the yarn interweaving point, - part of the wave will be transmitted along the original yarn to the other side of the interweaving point, the other part will be transferred to the inside of the interwoven yarn, and some will be reflected back along the original yarn to form the reflected wave. Among the above three kinds of fabrics, woven fabrics have the most interlacing points. After being hit by bullets, the kinetic energy of bullets can be transmitted through the interaction of yarns at the interlacing points, so that the impact force of bullets or shrapnel can be absorbed in a large area. But at the same time, the interweaving point also plays a fixed role. The reflection wave formed at the fixed end and the original incident wave will be superimposed in the same direction, which will greatly enhance the tensile effect of the yarn, and fracture after exceeding its breaking strength. In addition, some of the elastic pieces in the fabric may be pushed apart by small pieces of yarn. In one Within a certain range, if the fabric density is increased, the possibility of the above situation can be reduced and the strength of woven fabric can be improved, but the negative effect of stress wave reflection superposition will be enhanced. Theoretically, the best impact resistance is obtained by using unidirectional materials without interlacing points. This is the starting point of "shield" technology. The starting point of technology. "Shield" technology, namely "unidirectional array" technology, is the United signal company of the United States
In 1988, the company launched and obtained a patent for the production of high-performance non-woven bulletproof composite materials. The right to use the patented technology has also been granted to DSM. The fabric made by this technology is weft free fabric. Weft free cloth is made of unidirectional parallel arrangement of fibers and bonding with thermoplastic resin. At the same time, the fibers are crossed between layers and pressed with thermoplastic resin. Most of the energy of a bullet or fragment is absorbed by stretching and breaking the fibers near the impact point or impact point. "Shield" fabric can keep the original strength of the fiber to the maximum extent, and quickly disperse the energy to a large range, and the processing process is relatively simple. The laminated single-layer weft free cloth can be used as the main structure of soft bulletproof vests, and the multi-layer pressing can be used as rigid bulletproof materials such as bulletproof reinforced inserts. If it is said that most of the elastic energy is absorbed at the impact point or the fiber near the impact point by excessive stretching or piercing, the bulletproof mechanism of the fabric with needle punched nonwovens can not be explained.
Summary
Because experiments have shown that there is almost no fiber fracture in needle punched nonwovens. Needle punched nonwovens are composed of a large number of staple fibers without interlacing points and almost no fixed point reflection of strain wave. Its bulletproof effect depends on the diffusion speed of bullet impact energy in felt. It has been observed that after being hit by shrapnel, there is a roll of fibrous material at the top of the fragment simulator (FSP). Therefore, it is predicted that the projectile or shrapnel will become blunt at the initial stage of projectile impact, making it difficult to penetrate the fabric. It is pointed out in many research materials that the modulus of fiber and the density of felt are the main factors affecting the bulletproof effect of the whole fabric. Needle punched nonwovens are mainly used in bulletproof vests.
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