Kevlar, formerly known as KEVLAR in English, is also translated as Kevlar or Kevlar. The original name of the material is “poly(p-phenylene terephthalamide)”, and the repeating unit of the chemical formula is -[CO-C6H4-CONH-C6H4-NH-]-The amide group attached to the benzene ring is a para structure (the meta structure is another product with a brand name of Nomex, commonly known as fireproof fiber).
Development background
In the 1960s, DuPont developed a new type of aramid fiber composite material —- Aramid 1414. This aramid fiber composite material was officially commercialized in 1972 and the product was registered as a trademark of Kevlar. Models are divided into K29, K49, K49AP and so on.
Because this new material has low density, high strength, good toughness, high temperature resistance, easy processing and forming, its strength is five times that of steel of the same quality, but its density is only one-fifth of steel.(The density of Kevlar is 1.44 grams per cubic centimeter, and the density of steel is 7.859 grams per cubic centimeter). Due to the toughness and wear resistance of Kevlar brand products, the combination of rigidity and flexibility,Has the special ability to be invulnerable. It is called “Armored Guard” in the military.
Application field
In the 21st century, the composite armor of “Kevlar” laminated sheet and steel and aluminum plates has not only been widely used in tanks, armored vehicles, body armor, but also used in nuclear powered aircraft carriers and guided missile destroyers.
The protective performance and maneuverability of the above-mentioned weapons have been greatly improved. The composite material of “Kevlar” and ceramics such as boron carbide is an ideal material for the manufacture of helicopter cockpit and driver’s seat. According to the test,
It resists armor-piercing bullets much better than fiberglass and steel armor. In order to improve the survivability of battlefield personnel, people pay more and more attention to the development of bulletproof vests. “Kevlar” material is still made ideal material for body armor. It is reported that replacing nylon and glass fiber with “Kevlar” material can at least double its protective ability under the same conditions, and has good flexibility, comfortable to wear. Bulletproof vests made of this material are only 2 to 3 kilograms in weight and are easy to wear and move, so they have been adopted by police and soldiers in many countries.
Performance parameters
Mechanical properties
Strength: 3.6 GPa
Elongation modulus: 131 GPa
Elongation at break: 2.8 %
Thermal properties:
Long-term use temperature: 180°C
Axial thermal expansion coefficient: -2 x 10 ^(-6)/K
Thermal conductivity: 0.048 W(m-K)
Kevlar fiber properties
1. Permanent heat resistance and flame retardancy, the limiting oxygen index Loi is greater than 28.
2. Permanent antistatic property.
3. Permanent acid and alkali and organic solvent erosion.
4. High strength, high wear resistance and high tear resistance.
5. In case of fire, no molten droplets will be produced, and no toxic gas will be produced.
6. When the cloth is burned, the cloth will be thickened to enhance the sealing and not break.
