Kevlar fabric. Kevlar fabric: material stronger than steel What is Kevlar used for?
Kevlar fiber has a characteristic golden yellow color. The diameter of the elementary fiber is 10 microns.
Kevlar K-29 (1975) - used in industry for the manufacture of cables, brake pads, personal armor and armor for combat vehicles. Kevlar K49 is a brand of high-modulus fiber used in the cable industry, for the manufacture of optical fiber braiding, for the manufacture of ropes, and for plastic reinforcement. Kevlar K100 is factory dyed yarn. Kevlar K119 - high elongation, flexible and has increased fatigue strength. Kevlar K129 is a grade of high-strength armor fiber. Kevlar AP is 15 percent stronger than K-29. Kevlar XP is a composition based on a high viscosity resin and the new KM2plus fiber. Kevlar KM2(1992) - brand of fiber for producing fabric that meets the requirements for body armor and body armor.
Application [ | ]
The material was originally developed for reinforcing car tires, for which it is still used today. In addition, Kevlar is used as a reinforcing fiber in composite materials, which are strong and lightweight.
Kevlar is used to reinforce copper and fiber optic cables (thread along the entire length of the cable, preventing stretching and breaking of the cable), in speaker cones, and in the prosthetic and orthopedic industry to increase the wear resistance of parts of carbon fiber feet.
Kevlar fiber is also used as a reinforcing component in mixed fabrics, giving products made from them resistance to abrasive and cutting influences; in particular, protective gloves and protective inserts in sportswear (for motorsports, snowboarding, etc.) are made from such fabrics .). It is also used in the shoe industry to make anti-puncture insoles.
Personal armor protection[ | ]
Fragments of a Kevlar fabric-polymer helmet used in combat to absorb the energy of a hand grenade explosion, northeastern Iraq, 2004. The squad personnel were rescued; Corporal Dunham, who covered the grenade with his helmet, was killed.
The mechanical properties of the material make it suitable for the manufacture of personal armor protection (PIB) - body armor and body armor. Research in the second half of the 1970s showed that Kevlar-29 fiber and its subsequent modifications, when used in the form of multilayer fabric and plastic (fabric-polymer) barriers, provide the best combination of energy absorption rate and duration of interaction with the striker, thereby providing relatively high, given the mass of the obstacle, indicators of bulletproof and anti-fragmentation resistance. This is one of the most famous uses of Kevlar.
Kevlar has a relatively low weight, but a significant force of internal friction, which allows you to quickly dissipate kinetic energy during a collision, turning it into heat. At the same time, due to its thinness, it is not able to stop sharp and heavy objects that have a large impulse, for example, a rifle bullet or a bayonet blade. For this reason, in modern army body armor it is combined with additional protective plates made of steel, titanium or ceramics, which are short-lived, but can save a soldier’s life in battle, as well as with shock-absorbing elements to reduce the armor effect of projectiles.
In the 1970s, one of the most significant advances in the development of body armor was the use of Kevlar fiber reinforcement. The development of Kevlar body armor by the US National Institute of Justice took place over several years in four stages. In the first stage, the fiber was tested to determine whether it could stop a bullet. The second phase was to determine the number of layers of material needed to prevent penetration by bullets of different calibers and traveling at different speeds, and to develop a prototype vest capable of protecting employees from the most common threats: .38 Special and .22 Long Rifle caliber bullets. By 1973, a seven-layer Kevlar fiber vest was developed for field testing. It was found that when wet, the protective properties of Kevlar deteriorated. The ability to protect against bullets also decreased after exposure to ultraviolet light, including sunlight. Dry cleaning and bleaches also negatively affected the protective properties of the fabric, as did repeated washing. To overcome these problems, a waterproof vest has been developed that has a fabric coating to prevent exposure to sunlight and other harmful factors.
Shipbuilding [ | ]
Since the early 1990s, Kevlar has become widespread in shipbuilding. Due to technological difficulties and the price of Kevlar, it is used selectively. For example, only in the keel part or at the seams. Many manufacturers (such as the shipyards BAIA Yachts, Blue water, Dolphin, Danish yacht, Zeelander Yachts), making not a very large number of yachts per year, are systematically switching to using Kevlar. One of the leaders in the production of Kevlar yachts is [ by whom?] Italian shipyard Cranchi, which produces Kevlar yachts ranging in size from 11 to 21 meters.
Modern high-tech materials are increasingly being used in a variety of industries. One of them is Kevlar fabric. This element is distinguished from other means by its excellent resistance to both friction and pinpoint impact. Thus, in composite materials it is most often combined with a variety of materials; in turn, in the textile industry, Kevlar fabric has found wide application. Such high-tech material as Kevlar is used for sewing jackets, jeans, gloves, for the production of cables and much more.
Characteristics of Kevlar fabric
Kevlavr fabric is actively used as a reinforcing agent for a variety of composite materials. Kevlar fabric has high strength, with very low weight. Such a product not only does not lose its properties under the influence of low temperatures (the temperature limit is -190 degrees), but also acquires additional strength.
Exposure to high temperatures will also not cause much harm to Kevlar fabric, because its destruction temperature ranges from +430 to +480 degrees. Moreover, the destruction temperature completely depends on the time and intensity of heating. In order to reduce the cost of finished products, the production of combined fabrics has been established, to which fiberglass or coal fibers are added. Kevlar fabric poses absolutely no threat to human health.
The high heat resistance and strength of Kevlar fabric allows it to be used for the manufacture of uniforms for firefighters. Due to the fact that Kevlar is 5 times stronger than steel (at the same weight), it has become possible to use it for the manufacture of body armor. It was special protective devices, their fairly successful production, that largely contributed to the popularity of Kevlar fabric. Now such material is used in a variety of industries, including aerospace.
Operation of Kevlar fabric
In everyday life, Kevlar has also found very wide application. Most often it is used precisely where high resistance to low and high temperatures is required, and, accordingly, its highest strength. Typically, Kevlar fabric is used to produce various equipment for athletes (helmets, ropes, gloves, etc.). In addition, as mentioned earlier, Kevlar fabric is actively used in the production of composite materials.
However, in terms of temperature and strength indicators, Kevlar is slightly inferior to carbon fiber, but at the same time, it tolerates bending loads much better. In an attempt to combine the qualities of these two materials, combined Kevlar fabrics were created, with approximately equal amounts of both materials. Such fabrics tolerate elastic deformation very well. But carbon-Kevlar fabric loses strength, has slightly more weight and does not tolerate contact with water very well.
However, the combination of epoxy resins with Kevlar fabric is not ideal. Such resins tend to “pick up” moisture and accumulate it in themselves. When in contact with water, Kevlar significantly loses its properties, which are so high in its dry state. In addition, ultraviolet light is a catalyst that reduces the lifespan of the Kevlar component.
That is why it is advisable to use Kevlar only in certain conditions (using absolutely all the positive characteristics of the material), which does not actually reduce its demand at the present time. Kevlar fabric is used for sewing construction-special work clothing (assembly gloves, welding overalls, etc.).
Kevlar is a registered trademark of para-aramid synthetic fiber and belongs to the broad group of aramid fibers such as Nomex and Technora. Developed by DuPont in 1965, this high-strength material was first commercialized in the early 1970s as a replacement for steel in racing tires. Typically, Kevlar is distributed in the form of cables or fabric, which can be used alone or as an element in composite composite materials.
Currently, Kevlar has many applications, ranging from bicycle tires and sails of yachts and other ships to body armor (due to its high tensile strength-to-weight ratio; in this indicator, Kevlar is 5 times superior to steel). It is also used by the prosthetic and orthotic industry to increase the wear resistance of carbon fiber foot parts. Kevlar is used to make speaker cones.
A similar fiber called Twaron, with approximately the same chemical structure, was developed by Akzo specialists in the 70s of the last century, and its commercial production began in 1986. Currently, Twaron fiber is produced by Teijin.
Polyparaphenylene terephthalamide - which is sold under the brand name Kevlar - was invented by Polish-American chemist Stephanie Kwolek while she was working at DuPont. The reason for the start of the development of a new substance was the brewing shortage of gasoline at that time. In 1964, Kwolek's group began searching for a new lightweight, strong fiber for use in lightweight yet durable tires. At that time she was working with a number of polymers - polybenzamide and poly/p-phenylene terephthalate. Based on these components, the researcher was able to obtain a fiber that, unlike nylon, was not brittle. By 1971, a modern example of Kevlar had been obtained. However, Kwolek was not actively involved in the development of Kevlar products and its applications.
1. History
2 Production
3 Structure and properties
4 Thermal properties
5 Applications
5.1 Protection
5.1.1 Cryogenics
5.1.2 Armor
5.1.3 Personal protective equipment
5.2 Sports equipment
5.2.1 Shoes
5.3 Music
5.3.1 Audio equipment
5.3.2 Strings
5.3.3 Drums
5.4 Other applications
5.4.1 Dancing with fire
5.4.2 Pans
5.4.3 Ropes, cables, sheaths
5.4.4 Electricity generation
5.4.5 Construction of buildings
5.4.6 Brakes
5.4.7 Temperature compensators and hoses
5.4.8 Particle physics
5.4.9 Smartphones
6 Composite materials
Production
Kevlar is synthesized in solution from the monomers phenylene-1,4-diamine (p-phenylenediamine) and terephthaloyl chloride using a condensation reaction. Hydrochloric acid is a by-product in this case. The result is a substance with the characteristics of liquid crystals, the polymer chains of which are oriented in one direction, which allows the formation of a strong fiber. Hexamethylphosphoramide (HMPA) was originally used as a polymerization solvent, but for safety reasons DuPont replaced it with a solution of N-methylpyrrolidone and calcium chloride. Since this process had already been patented by Akzo (see above) for the production of Twaron, DuPont's move triggered patent litigation.
Reaction of phenylene-1,4-diamine (p-phenylenediamine) and terephthaloyl chloride resulting in Kevlar
The production of Kevlar (polyparaphenylene terephthalamide) is a relatively expensive process due to the difficulties associated with using the concentrated sulfuric acid required to maintain the water-insoluble polymer in solution during its synthesis and fiber formation.
There are several grades of Kevlar available:
Kevlar K-29 - used in industrial applications such as cables, asbestos substitutes, brake pads, body/vehicle armor;
Kevlar K49 is a high modulus material used in cables and ropes;
Kevlar K100 - colored version of Kevlar;
Kevlar K119 - has high elongation, flexibility and relatively high fatigue strength;
Kevlar K129 - characterized by higher strength compared to standard Kevlar; widely used for ballistic applications;
Kevlar AP - 15% higher tensile strength than K-29;
Kevlar XP is a combination of lightweight resin and KM2 fibers;
Kevlar KM 2 - improved ballistic characteristics, used in the creation of armor.
Exposure to the ultraviolet component of sunlight leads to the degradation and disintegration of Kevlar. Therefore, it is rarely used outdoors without protection from sunlight.
Structure and properties
Once formed, Kevlar fibers have a tensile strength of about 3620 MPa and a relative density of 1.44. The polymer owes its high strength to the many bonds between monomers. These bonds have a greater effect on the properties of Kevlar than van der Waals forces and chain length, which typically affect the properties of other synthetic polymers and fibers such as Dyneema. The presence of salts and some other impurities, especially calcium, can affect the properties of the final product, and during production they try to avoid including impurities in the composition of Kevlar.
Thermal properties
Kevlar retains strength and elasticity down to cryogenic temperatures (-196°C). In fact, at low temperatures it becomes a little stronger. At higher temperatures, tensile strength is immediately reduced by about 10-20%, and after several hours of continuous heat exposure, tensile strength is reduced even more. For example, at 160 °C (320 °F), a 10% reduction in strength occurs after approximately 500 hours of thermal exposure. At 260 °C (500 °F), a 50% reduction in strength occurs after 70 hours of exposure to a heat source.
Applications
Protection
Cryogenics (low temperature physics)
Kevlar is often used in the field of low temperature physics. This is due to its low thermal conductivity and high strength compared to other materials that are used to create suspensions. The most common use of Kevlar is to separate the reservoir of paramagnetic salts from the core of a superconducting magnet in order to minimize heat leakage into the paramagnetic material. It is also used in creating [structural] stiffeners or structural support for applications where low heat leakage is required.
Armor
Kevlar is a fairly well-known and popular component of personal armor such as combat helmets, ballistic face masks and ballistic vests. Kevlar is a key component of the PASGT helmet and body armor and its equivalents, which have been used by the United States Armed Forces since 1980. Other military applications include bulletproof masks used by guards and balaclavas used to protect armored vehicle crews. Even the Nimitz-class aircraft carriers use Kevlar armor along vital spaces. If we consider the civilian use of the material, it should be noted that it is used in equipment to protect emergency response workers if the scope of their activity involves contact with objects that have a high temperature (for example, fire fighting). This area also includes body armor made of Kevlar, which is used by police officers, private security forces of private organizations and special forces.
Individual protection means
Kevlar is used to make gloves, sleeves, jackets, pants and other items of clothing that are designed to protect users from cuts, abrasions and heat. Protective gear made from Kevlar is often significantly lighter and thinner than equivalents made from more traditional materials.
Sport equipment
It is used as an inner lining for some bicycle tires to help prevent punctures. In table tennis, layers of Kevlar are added to rackets to increase bounce and achieve weight savings. It is used in the production of safety clothing for motorcyclists, especially in shoulder and elbow protection. In Kyudo, the Japanese art of archery, Kevlar fibers can be used to create a bowstring. In this case, the material acts as an alternative to more expensive hemp fibers. This material is most often used to create support cables for paragliders. In fencing, it is used to create protective jackets, trousers, breastplates and mask elements. Tennis rackets often also contain Kevlar elements. It is even used in sails for high performance racing boats. Kevlar is increasingly used in "peto" - the soft covering that protects picador horses in the arena.
Shoes
For the first time in the footwear industry, Nike took advantage of advances in the technology of creating products based on Kevlar. Its specialists used Kevlar in a series of Elite Series II sneakers (an improved version of an earlier version of basketball sneakers). This was done to reduce the elasticity of the shoe's toe. Previously, nylon was used for this purpose, but Kevlar expanded by about 1% compared to nylon, which expanded by about 30%. The company now produces similar shoes under the brands LeBron, HyperDunk and Zoom Kobe VII. However, these sneakers were introduced in a price range that is much higher than the average cost of basketball shoes.
Kevlar has also been used as speed control patches on some Soap Shoes, and has also served as the lace material for the Adidas F50 adiZero Prime premium football boots.
Music
Sound equipment
Kevlar has also been found to have beneficial acoustic properties. Currently, fabrics based on it are used to create diffusers for acoustic speakers (low and medium frequencies). Additionally, Kevlar is used as a strength element in fiber optic cables, such as those used to transmit audio data.
Strings
Kevlar can be used as an acoustic core in strings for stringed instruments. The physical properties of Kevlar give strings strength, flexibility and stability. Today, the only manufacturer of this type of string is CodaBow.
Drums
Kevlar is sometimes used as a material for marching snare drums (with strings along the bottom head). Its use allows us to achieve a very high tension, resulting in a fairly clear sound at the output. Typically, Kevlar is coated with a layer of resin to seal it, and a layer of nylon is added on top to provide a flat striking surface.
Other Applications
Dancing with fire
Wicks for fire dancing props are made from composite materials that contain Kevlar. Kevlar itself does not absorb flammable substances well, so it is mixed with other materials such as fiberglass or cotton. The high heat resistance allows Kevlar wicks to be reused quite a few times.
Frying pans
Kevlar is sometimes used as a substitute for Teflon coating by some nonstick pan manufacturers.
Ropes, cables, sheaths
Kevlar is used in braided ropes and cables, where the Kevlar fibers are grouped in parallel and covered on the outside with a polyethylene sheath. Cables are used in suspension bridges. Kevlar is widely used as a protective outer sheath for fiber optic cables (the material protects the cable from damage and kinking).
Kevlar woven shells are produced by the following companies:
A.W. Chesterton Company(chesterton.com). Its product, Chesterton 1740, is an intermediate braid made of Kevlar fiber and polytetrafluoroethylene (Teflon, PTFE). Key characteristics of Chesterton 1740: temperature limit - 260 °C (500 °F), chemical resistance - pH 4-11, pressure limit 20 bar/g (300 psi). Each strand of fiber is individually coated with PTFE to better dissipate heat. Chesterton 1740 offers various combinations of midsleeve components to achieve the desired resistance to pressure, temperature, chemicals and wear.
Company Diflon(diflo n.it) offers woven sheaths KV series (-100 - 400 °C; 50 - 100 bar), consisting of Kevlar fibers and polytetrafluoroethylene. The shells are characterized by increased heat resistance. This shell does not stain adjacent surfaces, has a low coefficient of friction and dissipates heat. Applications: wastewater treatment, sluice system, low pressure valves, piston engine shafts, handling acids, alkalis, oil. The product has universal application, except for working with oxygen, strong alkalis and oxidizing agents. The product is suitable for the paper industry, petrochemical and chemical industries and power stations.
Product DEPACAnstaltEstablishment(depac.at) is an excellent alternative to asbestos-based braiding. Kevlar braiding is particularly effective in hard materials handling and in the paper industry, steel mills, wastewater treatment plants, and sugar industries. DEPAC's special 4-piece high-density diagonal weave combines chemical resistance with high strength to ensure optimal sealing with minimal contact pressure.
Electricity generation
Kevlar was used by scientists from the Georgia Institute of Technology (USA) as the basis for an experiment to create clothing that can generate electricity. This was done by weaving zinc oxide nanowires into fabric. If the project is successful, the new fabric will generate about 80 milliwatts per square meter.
Building
The retractable Kevlar roof, covering more than 5,500 square meters, was a key part of the Montreal Olympic Stadium design for the 1976 Summer Olympics. This construction was incredibly unsuccessful, as the roof was completed ten years late, and after another ten years (at the end of May 1998) it had to be replaced after a number of problems.
Brakes
Stapled fiber has been used as a replacement for asbestos in brake pads. Dust, which is a byproduct of asbestos-based brakes, is highly toxic, while aramid fibers are a better option.
Temperature compensators and hoses
Kevlar can be used as a reinforcing layer in rubber bellows pipe expansion joints and rubber hoses, which are intended for use in high temperatures and must have high strength. It can also be used as a layer of braid used on the outside of a fire hose to add a greater degree of protection against sharp objects.
Particle physics
A thin Kevlar window was used in the NA48 experiment at CERN. The material was used to separate the vacuum chamber from the atmospheric pressure chamber. A series of experiments in particle physics NA48 concerned the study of the mechanism of kaon decays. More than 100 physicists, mainly from Western Europe and Russia (JINR), took part in the scientific work.
Smartphones
The Motorola RAZR line of smartphones is distinguished by the presence of a Kevlar rear casing. Device developers chose this material over others, such as carbon fiber, due to its resistance to mechanical stress and lack of interference with signal transmission.
Composite materials
Aramid fibers are widely used to reinforce composite materials, often the same Kevlar is used in combination with carbon fiber and glass fiber. The matrix for high-performance composites is typically epoxy resin. Typical applications include the production of monocoques for F1 racing cars (a type of space-frame construction in which (as opposed to frame or frame structures) the outer shell is the main and usually the only load-bearing element); helicopter blades, equipment for tennis, table tennis, badminton and squash, production of kayaks, cricket bats, field hockey sticks and lacrosse sticks.
Currently, Kevlar has become a common component of clothing and equipment for people whose lives are constantly in danger: military and security officials, astronauts and researchers, athletes and firefighters. Kevlar fibers are used wherever increased strength is required, from car tires to yacht hulls, the scope of their application is constantly expanding, and the production technology is being improved. This material was received half a century ago, and many will find it strange that its author was a woman.
How did Kevlar come about?
It is symbolic that the inventor of this unique fiber, Stephanie Kwolek, loved to sew clothes for dolls as a child. After school, she majored in chemistry at Carnegie University, but dreamed of medicine. In order to earn money for studying at the university, in 1946 the girl began working at the famous DuPont concern, and soon realized that her calling was, after all, chemistry. In 1964, Kwolek's group worked to improve the production of polyaramids, polymer substances with a rod-like structure that could replace steel cord in tires. By abandoning the melt method, Stephanie was able to create an unusual-looking solution that, when passed through spinnerets, turned into aramid threads.
When the resulting fiber began to be tested for strength, the researchers decided that the equipment had broken down - the strength indicators of the new material were five times greater than those of steel.
The new material, called Kevlar, came into commercial use in the seventies. It began to be used for the production of tires, cord tapes, and composite materials. At the same time, military and law enforcement agencies drew attention to the high strength of polyaramid fibers, whose goal was to develop personal protective equipment. The idea of a bulletproof vest appeared during the First World War (its author was the writer Conan Doyle), but traditional metal plates were heavy and hampered movement.
Specialists from the American National Institute of Justice conducted thorough research for several years, during which they proved that resistance to bullet shots for the most common 38 caliber is provided by seven layers of Kevlar fabric. The last stage of field testing showed that the strength of such body armor decreases when it gets wet and when exposed to UV rays. It was also found that Kevlar fabric products deteriorate in their protective properties after several washes, and that they do not tolerate bleaching or dry cleaning.
The result of the developments was a Kevlar body armor coated with water-resistant fabric, which provides protection for the reinforced layer from water and sun. In addition, Kevlar helmets, gloves, shoe insoles, etc. began to be used as personal protective equipment.
Properties of aramid fibers
In addition to high strength, Kevlar has many other unique properties, namely:
- when in contact with fire and high temperatures, this fiber does not burn, does not smoke or melt;
- Kevlar is non-toxic and non-explosive;
- its thermal decomposition temperature is 430-450 degrees;
- the strength of armid fibers begins to gradually decrease when heated to more than 150 degrees;
- when frozen, Kevlar only becomes stronger, it is able to withstand cryogenic temperatures (up to -200 degrees);
- this material is an electrical insulator.
In addition, Kevlar fabric is soft, hygroscopic and air-exchangeable, and is quite comfortable to use. True, this does not apply to clothing designed to work in conditions of open fire and high temperatures. To increase heat resistance, Kevlar is coated with aluminum. Material made from such fiber reliably protects from powerful thermal radiation, contact with surfaces heated to 500 degrees, as well as from splashes of hot metal.
It should also be added that this material is quite light - one meter of fabric weighs 30-60 g, and although it is not cheap (from $30 per square meter), its excellent protective properties fully justify such costs. Protective materials reinforced with Kevlar threads are somewhat cheaper, which makes them resistant to tearing and abrasion. Such fabrics are used for protective inserts in work and sports clothing, gloves, and also as wear-resistant insoles. Caring for products made from them is extremely simple. They should not:
- wash often;
- clean with chemicals;
- expose to sunlight.
Where is Kevlar used?
This high-strength fiber finds a wide variety of applications - from the aviation and space industries to sports and travel clothing. Kevlar comes to the market in the form of threads, cord, fabric, and also as a component of composite and mixed materials. The main ways of its application are:
KEVLAR™- trade name of aramid - polyparaphenylene terephthalamide, a synthetic fiber with high strength (five times stronger than steel, tensile strength σ0 = 3620 MPa). Developed by the American company DuPont in 1965, its commercial use began in the early 1970s. Lightweight, durable and safe Kevlar material can significantly improve the performance characteristics of workwear and protective equipment. Today, Kevlar is used in the production of products that require high wear resistance of materials: climbing ropes, quickdraws, helmets, shoe uppers, backpacks, skis, gloves, as well as for the manufacture of workwear. Kevlar fiber is lightweight and highly resistant to various types of impacts. It has properties such as non-flammability and heat resistance. According to the developers, Kevlar fibers are five times stronger than steel for equal weight.
Area of application of Kevlar
Initially, the material was developed for reinforcing car tires, and is still used in this capacity today. In addition, Kevlar is used as a reinforcing fiber in composite materials, which are strong and lightweight.
Kevlar is used to reinforce copper and fiber optic cables (thread along the entire length of the cable, preventing stretching and breaking of the cable), in speaker cones, and in the prosthetic and orthopedic industry to increase the wear resistance of parts of carbon fiber feet.
Kevlar fiber is also used as a reinforcing component in mixed fabrics, giving products made from them resistance to abrasive and cutting influences; in particular, protective gloves and protective inserts in sportswear (for motorsports, snowboarding, etc.) are made from such fabrics .).
In workwear, fabric with Kevlar fiber is used mainly for reinforcing pads in the knee area (knee pads) and elbow area. Because Kevlar fabric has high abrasion resistance, so it is used in clothing in those places where the greatest stress is on abrasion, cuts and punctures.
Use in body armor
Kevlar structure. The high degree of order of the polymer and its strength are provided by intermolecular hydrogen bonds.
The mechanical properties of the material make it suitable for the manufacture of bulletproof vests. This is one of the most famous uses of Kevlar.
In the 1970s, one of the most significant advances in the development of body armor was the use of Kevlar fiber reinforcement. The development of Kevlar body armor by the National Institute of Justice took place over several years in four stages. In the first stage, the fiber was tested to determine whether it could stop a bullet. The second step was to determine the number of layers of material needed to prevent penetration by bullets of different calibers traveling at different speeds, and to develop a prototype vest that could protect employees from the most common threats: .38 Special and .22 Long Rifle bullets. By 1973, a seven-layer Kevlar fiber vest was developed for field testing. It was found that when wet, the protective properties of Kevlar deteriorated. The ability to protect against bullets also decreased after exposure to ultraviolet light, including sunlight. Dry cleaning and bleaches also negatively affected the protective properties of the fabric, as did repeated washing. To overcome these problems, a waterproof vest has been developed that has a fabric coating to prevent exposure to sunlight and other harmful factors.
Shipbuilding
In the last decade, Kevlar has become widespread in shipbuilding. Due to the technological difficulties and price of Kevlar, it is used selectively. For example, only in the keel part or at the seams. Many manufacturers (such as the shipyards BAIA Yachts, Blue water, Danish yacht, Zeelander Yachts), making not a very large number of yachts per year, are systematically switching to using Kevlar. The leader in the production of Kevlar yachts is the Italian shipyard Cranchi, which produces Kevlar yachts ranging in size from 11 to 21 meters.
Aviation industry
Kevlar is used in the design of a number of unmanned aerial vehicles (such as the RQ-11) to improve protection.
Temperature properties
Kevlar retains strength and elasticity at low temperatures, down to cryogenic temperatures (−196 °C), moreover, at low temperatures it even becomes slightly stronger.
When heated, Kevlar does not melt, but decomposes at relatively high temperatures (430-480 °C). The decomposition temperature depends on the heating rate and the duration of exposure to temperature. At elevated temperatures (over 150 °C), the strength of Kevlar decreases over time. For example, at a temperature of 160 °C, the tensile strength decreases by 10-20% after 500 hours. At 250°C, Kevlar loses 50% of its strength in 70 hours.