Body armor is "a kind of clothing that can absorb and dissipate the kinetic energy of warheads and fragments, prevent penetration and effectively protect the protected parts of human body". In terms of use, bulletproof vests can be divided into two types: police type and military type. From the perspective of materials, bulletproof vests can be divided into three types: software, hardware and soft-hard complex. The material of soft bullet-proof vest is mainly high-performance textile fiber, which is much higher than the energy absorption capacity of ordinary materials, giving bullet-proof function to bullet-proof vest. Moreover, because this kind of bullet-proof vest generally adopts textile structure and has considerable flexibility, it is called soft bullet-proof vest. Hardware body armor is made of special steel plate, super-strong aluminum alloy and other metal materials or hard nonmetallic materials such as alumina and silicon carbide, and the body armor made of it is generally not flexible. The softness of soft and hard composite bulletproof vests is between the above two types. It is a composite bulletproof vest with soft material as lining and hard material as panel and reinforcing material.
As a kind of protective equipment, bulletproof performance is the first core performance of bulletproof vest. At the same time, as a functional garment, it should also have certain wearability.
Bulletproof performance
The bulletproof performance of body armor is mainly reflected in the following three aspects: (1) pistol and rifle bullets. At present, many soft body armor can prevent pistol bullets, but to prevent rifle bullets or bullets with higher energy, ceramic or steel reinforcing plates are needed. (2) Bullet-proof Fragments Bombs, mines, artillery shells, grenades and other explosives explode with high-speed fragments, which is one of the main threats on the battlefield. According to the investigation, the order of threats faced by soldiers on a battlefield is: shrapnel, bullet, explosion shock wave and high temperature. Therefore, we should attach great importance to the role of bulletproof tablets. (3) bullets that prevent non-penetrating injuries will have a huge impact force after hitting the target, which is often fatal to the human body. This kind of injury is not penetrating, but it will cause internal injuries, the most serious of which is life-threatening. Therefore, preventing non-penetrating injuries is also an important aspect of bulletproof performance of bulletproof vests.
abrasiveness
On the one hand, the wearing performance requirements of bulletproof vests mean that bulletproof vests should be as light and comfortable as possible, and people can still perform various actions flexibly after wearing them. On the other hand, it is the ability of clothing to adjust the microclimate environment of "clothing-human body" system. For bulletproof vests, it is hoped that people can still maintain the basic heat and moisture exchange state of "people-clothes" after wearing bulletproof vests, so as to avoid discomfort caused by moisture accumulation on the inner surface of bulletproof vests as much as possible, such as sultry humidity, and reduce body consumption. In addition, due to its special use environment, the body armor should also consider the adaptability with other weapons and equipment.
Development course of bulletproof vest
Bullet-proof vest, as an important personal protective equipment, has experienced the transformation from metal armor plate to nonmetal synthetic material, and the development process from homozygous material to composite system of synthetic material, metal armor plate and ceramic protective plate. The rudiment of human body armor can be traced back to ancient times. In order to prevent the body from being hurt, primitive people used natural fiber woven belt as the material of chest protection. The development of weapons forces the corresponding progress of human armor. As early as the end of19th century, the silk used in Japanese medieval armor was also used in American-made bulletproof vests. 190 1 year, William? After the assassination of President McKinley, bulletproof vests attracted the attention of the US Congress. Although this bulletproof vest can prevent low-speed pistol bullets (bullet speed 122 m/s), it can't prevent rifle bullets. Thus, in the First World War, bulletproof vests made of natural fiber fabrics and steel plates appeared. Thick silk clothing used to be the main component of bulletproof vests. However, silk quickly deteriorated in the trenches. This defect, coupled with the limited bullet-proof ability and high cost of silk, made the silk bullet-proof vest ignored by the American ordnance department in World War I and failed to be popularized. In World War II, the lethality of shrapnel increased by 80%, and 70% of the wounded died of trunk injuries. Participating countries, especially Britain and the United States, began to spare no effort to develop bulletproof vests. 1942 10 the British army successfully developed a bulletproof vest consisting of three high-manganese steel plates for the first time. 1943, as many as 23 kinds of body armor were trial-produced and officially adopted in the United States. The bulletproof vests in this period were mainly made of special steel. 1In June, 945, the US military successfully developed a bulletproof vest made of aluminum alloy and high-strength nylon, model M 12 infantry bulletproof vest. Among them, nylon 66 (polyamide 66 fiber) is a synthetic fiber which was invented shortly at that time. Its breaking strength (gf/d: g/denier) is 5.9 ~ 9.5, its initial modulus (gf/d) is 2 1 ~ 58, and its specific gravity is 1. 14 g/(cm. During the Korean War, the U.S. Army was equipped with T52 full nylon body armor made of 12 layers of bulletproof nylon, while the Marine Corps was equipped with M 195 1 rigid "Duo Long" glass fiber reinforced plastic body armor, weighing between 2.7 and 3.6 kilograms. The body armor made of nylon can provide a certain degree of protection for soldiers, but it is large and weighs as much as 6 kilograms. In the early 1970s, DuPont Company of the United States successfully developed a synthetic fiber with ultra-high strength, ultra-high modulus and high temperature resistance-Kevlar fiber, which was quickly applied to the bulletproof field. The appearance of this kind of high-performance fiber greatly improves the performance of soft textile bulletproof vest, and also improves the comfort of bulletproof vest to a great extent. The US military took the lead in using Kevlar to make bulletproof vests, and developed two models, light and heavy. The new bulletproof vest is made of Kevlar fabric as the main material and bulletproof nylon cloth as the envelope. Among them, the light bulletproof vest consists of 6 layers of Kevlar fabric, with a medium weight of 3.83 kg. With the commercialization of Kevlar, its excellent comprehensive performance makes it widely used in bulletproof vests of armies in various countries. With the success of Kevlar, the appearance of Twaron and Spectra, and their application in bullet-proof vests, soft bullet-proof vests characterized by high-performance textile fibers have gradually become popular, and their application scope is not limited to the military, but gradually extended to the police and political circles. But for high-speed bullets, especially bullets fired by rifles, pure soft body armor is still powerless. For this reason, people have developed soft and hard composite bulletproof vests, using fiber composite materials as reinforcing plates or plates to improve the bulletproof ability of the whole bulletproof vests. To sum up, there are three generations of modern body armor: the first generation is hard body armor, mainly made of special steel, aluminum alloy and other metals. This bullet-proof vest is characterized by its heavy clothing, generally about 20kg, uncomfortable to wear, great restrictions on human activities, and certain bullet-proof performance, but it is easy to produce secondary fragments. The second generation bulletproof vests are soft bulletproof vests, usually made of high-performance fiber fabrics such as Kevlar. Light weight, usually only 2 ~ 3kg, soft texture, good fitness, comfortable to wear, good concealment when worn internally, especially suitable for daily wear by police, security guards or politicians. In terms of bulletproof ability, it can generally prevent bullets fired by pistols from 5 meters away, and will not produce secondary shrapnel, but it will be deformed greatly after being hit by bullets, which may cause certain non-penetrating damage. In addition, for bullets fired by rifles or machine guns, soft bulletproof vests with general thickness are difficult to resist. The third generation bulletproof vest is a composite bulletproof vest. Usually, lightweight ceramic sheets are used as the outer layer and high-performance fiber fabrics such as Kevlar are used as the inner layer, which is the main development direction of bulletproof vests at present.
Bulletproof mechanism of bulletproof vest and its influencing factors
Fundamentally speaking, there are two bullet-proof mechanisms of bulletproof vests: one is to bounce off the fragments formed by the fragmentation of the bullet body; The second is to release the kinetic energy of the warhead through bulletproof materials. The first bulletproof vest developed in the United States in the 1920s and 1930s was protected by overlapping steel plates attached to solid clothes. This kind of bullet-proof vest and similar hard bullet-proof vests play a bulletproof role by bouncing off bullets or shrapnel, or breaking bullets to consume their energy. The bulletproof mechanism of soft body armor with high-performance fiber as the main bulletproof material is mainly the latter, that is, the fabric with high-strength fiber as the raw material is used to "catch" bullets or shrapnel to achieve the purpose of bulletproof. The research shows that there are five ways for soft body armor to absorb energy: (1) fabric deformation, including the deformation in the direction of bullet incidence and the tensile deformation near the incident point; (2) Fabric destruction: including fiber fibrillation, fiber breakage, yarn structure disintegration and fabric structure disintegration; (3) Thermal energy: energy is dissipated in the form of thermal energy through friction; (4) Acoustic energy: the energy consumed by the sound emitted by the bullet after hitting the bulletproof layer; (5) Deformation of projectile. The bulletproof mechanism of the soft-hard composite bulletproof vest developed to improve its bulletproof ability can be summarized by "combining soft and hard". When the bullet hits the bulletproof vest, the first thing that affects it is the hard bulletproof material such as steel plate or reinforced ceramic material. During this instant contact, both the bullet and the hard bulletproof material may be deformed or broken, which consumes most of the energy of the bullet. As the cushion and the second line of defense of bulletproof vest, high-strength fiber fabric absorbs and diffuses the remaining energy of bullets and plays a buffering role, thus minimizing non-penetrating injuries. In these two bullet-proof processes, the former plays a major role in energy absorption, greatly reducing the penetration of projectiles, which is the key to bullet-proof. The factors affecting the bulletproof efficiency of bulletproof vests can be considered from two aspects: projectiles (bullets or shrapnel) and interactive bulletproof materials. As far as the projectile is concerned, its kinetic energy, shape and material are important factors that determine its penetration. Ordinary warheads, especially lead-core or ordinary steel-core bullets, will be deformed when they contact bulletproof materials. In this process, the bullet consumes a considerable part of kinetic energy, thus effectively reducing the penetration of the bullet, which is an important aspect of the bullet energy absorption mechanism. However, the situation is obviously different for shrapnel produced by bombs, grenades and other explosions or secondary fragments formed by bullets. These shrapnel are irregular in shape, sharp in edge, light in weight and small in volume, and do not deform after hitting bulletproof materials, especially soft bulletproof materials. Generally speaking, the speed of this kind of debris is not high, but it is large and dense. The key for soft bullet-proof clothing to absorb the energy of such debris lies in that the debris cuts, stretches and breaks the yarns of bullet-proof fabric, which causes the interaction between yarns in the fabric and between different layers of the fabric, leading to the overall deformation of the fabric. In these processes, the debris does external work, thus consuming its own energy. In the above two kinds of human energy absorption process, a small part of energy is also converted into heat energy through friction (fiber/fiber, fiber/bullet) and into sound energy through impact. In terms of bulletproof materials, bulletproof materials must have high strength, good toughness and strong energy absorption ability in order to meet the requirements of bulletproof clothing to absorb the kinetic energy of bullets and other projectiles to the maximum extent. At present, the materials used in bulletproof vests, especially soft bulletproof vests, are mainly 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 basically not suitable for human armor because of poor flexibility, low fracture work, difficult textile processing and high price. Specifically, the bulletproof effect of bulletproof fabric mainly depends on the following aspects: tensile strength, elongation at break and work of fiber, modulus of fiber, fiber orientation and stress wave propagation speed, fiber fineness, fiber assembly mode, fiber weight per unit area, yarn structure and surface characteristics, fabric structure, fiber mesh layer thickness, mesh layer or fabric layer number, etc. The performance of fiber materials used for impact resistance depends on the fracture energy of fiber and the speed of stress wave propagation. Stress wave needs to spread as soon as possible, and the fracture energy of fiber under high-speed impact should be improved as much as possible. The tensile fracture work of materials is the energy that materials have to resist external damage, and it is a function related to tensile strength and elongation deformation. Therefore, theoretically, the higher the tensile strength, the stronger the elongation and deformation capacity and the greater the energy absorption potential. However, in practical application, the materials used in body armor are not allowed to deform too much, so the fibers used in body armor must have high deformation resistance, that is, high modulus. The influence of yarn structure on bullet-proof ability is due to the difference of single fiber strength utilization rate and yarn overall elongation and deformation ability caused by different yarn fabrics. The fracture process of yarn depends on the fracture process of fiber at first, but the fracture mechanism is very different because it is an aggregate. The finer the fibers are, the closer they are to each other in the yarn and the more uniform the force is, thus improving the strength of the yarn. In addition, the straightness and parallelism of fiber arrangement in yarn, the number of inner and outer layer transfers, yarn twist and so on. All these have an important influence on the mechanical properties of yarns, especially the tensile strength and elongation at break. In addition, due to the interaction between yarn and yarn, yarn and elastomer, the surface characteristics of yarn will produce or strengthen or weaken the above two effects. The existence of grease and moisture on the yarn surface will reduce the resistance of bullets or shrapnel to penetrate the material, so people often need to clean and dry the material to find ways to improve the penetration resistance. Synthetic fibers with high tensile strength and high modulus are usually highly oriented, so the fiber surface is smooth and the friction coefficient is low. When these fibers are used in bulletproof fabrics, the ability of energy transfer between fibers is poor after being hit by bullets, and the stress wave cannot spread quickly, which also reduces the ability of fabrics to stop bullets. Ordinary methods to improve the surface friction coefficient, such as napping and corona finishing, will reduce the strength of fibers, while the method of fabric coating will easily lead to "welding" between fibers, resulting in the reflection of bullet shock waves in the transverse direction of yarns, which will lead to premature fiber breakage. In order to solve this contradiction, people have come up with various methods. The United States Lianxin Company introduced an air-wound fiber to the market, which increased the contact between the bullet and the fiber through the fiber winding inside the yarn. In US patent 5035 1 1 1, a method to improve the friction coefficient of yarns by using sheath-core structural fibers is introduced. The "core" of this fiber is high strength fiber, and the "skin" is fiber with slightly lower strength and higher friction coefficient, and the latter accounts for 5% ~ 25%. Another American patent, 525524 1, invented a similar method, that is, coating a thin layer of high-friction polymer on the surface of high-strength fiber to improve the resistance of fabric to metal penetration. The invention emphasizes that the coating polymer should have strong adhesion with the surface of high-strength fiber, otherwise the coating material peeled off in the impact process will be used as a solid lubricant between fibers, thus reducing the friction coefficient of the fiber surface. In addition to fiber properties and yarn characteristics, fabric structure is also an important factor affecting the bulletproof ability of bulletproof vests. Fabric structure types used in software bulletproof vests include knitted fabrics, woven fabrics, weft-free fabrics and needle-punched nonwovens. Knitted fabrics have high elongation, which is beneficial to improve wearing comfort. However, when used for impact resistance, this high elongation will lead to great non-penetrating damage. In addition, due to the anisotropic properties of knitted fabrics, they have different degrees of impact resistance in different directions. Therefore, although knitted fabrics have advantages in production cost and efficiency, they are generally only suitable for making stab-resistant gloves and fencing clothes. , and can't be completely used in bulletproof vests. At present, woven fabrics, weft-free fabrics and needle-punched nonwovens are widely used in bulletproof vests. Due to the different structures, the bulletproof mechanisms of these three fabrics are also different, and ballistics can't give a full explanation at present. Generally speaking, after a bullet hits the fabric, it will generate a radial vibration wave in the impact point area and propagate through the yarn at high speed. When the vibration wave reaches the interweaving point of the yarn, part of the wave will be transmitted to the other side of the interweaving point along the original yarn, the other part will be transmitted to the yarn interwoven with it, and the other part will be reflected back along the original yarn to form a reflected wave. Among the above three fabrics, woven fabrics have the most interweaving points. After being hit by a bullet, the kinetic energy of the bullet can be transferred through the interaction of yarns at the interweaving point, so that the impact force of the bullet or shrapnel can be absorbed in a larger area. But at the same time, the interweaving point virtually plays the role of a fixed end. The reflected wave formed at the fixed end and the original incident wave are superimposed in the same direction, which greatly enhances the tension of the yarn and breaks after exceeding its breaking strength. In addition, some small shrapnel may push away a single yarn in the woven fabric, thus reducing the penetration resistance of shrapnel. In 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, to obtain the best impact resistance, it is to use unidirectional materials without interweaving points. This is also the starting point of "shield" technology. "Shielding" technology, that is, "unidirectional arrangement" technology, is a method for producing high-performance non-woven bullet-proof composite materials, which was introduced and patented by United Signal Company of the United States in 1988. The right to use this patented technology has also been awarded to DSM in the Netherlands. The fabric made by this technology is a weft-free fabric. Weft-free cloth is made by arranging fibers in parallel along one direction and bonding them with thermoplastic resin, while crossing the fibers between layers and pressing them with thermoplastic resin. Most of the energy of bullets or shrapnel is absorbed by stretching and breaking fibers at or near the impact point. "Shielding" fabric can maintain the original strength of fiber to the greatest extent, and quickly disperse energy to a larger range, and the processing procedure is relatively simple. Single-layer weft-free cloth can be used as the skeleton structure of soft bulletproof vest, and multi-layer pressing can be used as hard bulletproof materials such as bulletproof reinforced insert plates. If most of the elastic energy in the above two kinds of fabrics is absorbed on the fibers at or near the impact point, and the fibers are excessively stretched or punctured and broken, then the bulletproof mechanism of needled nonwovens can't be explained. Because experiments show that needle-punched nonwovens hardly break fibers. Needle-punched nonwovens are composed of a large number of short fibers, with no interweaving points and almost no fixed-point reflection of strain waves. Its bulletproof effect depends on the diffusion speed of bullet impact energy in the felt. It is observed that after being hit by shrapnel, there is a roll of fibrous material on the top of the fragment simulation bomb (FSP). Therefore, it is predicted that the projectile or shrapnel will become dull at the initial stage of impact and it is difficult to penetrate the fabric. Many research data point out that the modulus of fiber and the density of felt are the main factors affecting the bulletproof effect of the whole fabric. Needle-punched nonwoven felt is mainly used for bulletproof sheets of military bulletproof vests.