The traditional bulletproof vest is mainly composed of a jacket and a bulletproof panel, and the jacket is mainly made of chemical fiber fabrics. This chemical fiber product is very light in weight and mainly plays the role of covering and protecting the bulletproof layer. The bulletproof layer is made of hard and soft materials such as metal, glass fiber reinforced plastic, ceramics, nylon, Kevlar (aramid), etc. Due to the large weight of the metal, glass fiber reinforced plastic, ceramics, and heavyweight, the convenience of the bulletproof vest is seriously affected. affect the activities of individuals. Therefore, relevant researchers have conducted research on the material of the bulletproof layer and have made great progress.

The main material used in body armor is ultra-high molecular weight polyethylene fiber (UHMWPE), which is currently the fiber with the highest specific strength and specific modulus in the world, with a molecular weight of 1 million to 5 million.
UHMWPE fiber is one of the three major high-performance fibers in the world today, and my country is a big country in chemical fiber. Now a number of UHMWPE fiber industrial production bases have been formed in China, and the Development is also a manifestation of a country's comprehensive strength. UHMWPE fibers are used in major military fields.
Properties of UHMWPE
1. High specific strength and high specific modulus. The specific strength is more than ten times that of the steel wire of the same section, and the specific modulus is second only to the super carbon fiber.
2. Low fiber density, the density is 0.97-0.98g/cm.
3. Low elongation at break, large work at break, and strong ability to absorb energy, so it has outstanding impact resistance and cutting resistance.
4. High friction coefficient.
5. Chemical corrosion resistance, wear resistance and long flex life.
6. Anti-ultraviolet radiation, anti-neutron and gamma rays, high specific energy absorption, low dielectric constant and high electromagnetic wave transmittance.
In recent years, PE fiber has gradually become the main material of protective equipment. It is a high-performance organic fiber successfully developed in the early 1980s, and it is also one of the three major high-tech fibers (carbon fiber, aromatic fiber, PE fiber) in the world today. PE fiber has high axial specific tensile strength and stiffness, the specific strength is the highest among all fiber materials, and the specific modulus is second only to high-modulus carbon fiber (but carbon fiber is brittle and is not suitable for human body bulletproofing). Main body material), the specific energy absorption performance is the highest among all fibers, the low temperature resistance, the UV resistance are excellent, and the water resistance is also excellent. We all know that white plastic bags will not degrade for 100 years in the atmospheric environment, and this plastic is actually PE fiber as the raw material. It is a bad thing that PE in life does not degrade and pollutes the environment, but this feature is not desired in bulletproof products, indicating that it has good resistance and long life.
In addition, from the perspective of ballistic resistance, the ballistic resistance of PE fiber is about 30% higher than that of aramid in terms of low-speed bullet resistance; in terms of high-speed bullet resistance, the performance of PE fiber is 1.5 to 2 times that of aramid. It can be said that the shortcomings of aramid fibers have become the advantages of PE fibers, and the advantages of aramid fibers have become better in PE fibers, so it is an inevitable trend for PE fibers to replace aramid fibers in the field of protection.
Of course, PE fiber also has shortcomings, and its temperature resistance grade is far less than that of aramid fiber. The use temperature of PE fiber protection products is within 70°C (which can meet the requirements of human body and equipment, that is, the requirement of temperature resistance of 55°C). If the temperature exceeds this temperature, the performance will decline rapidly. When the temperature exceeds 150°C, the PE fiber will melt, while the aramid fiber will melt. The fiber can still maintain good protective performance at 200 °C, and it will not drip or decompose at 500 °C; when it suddenly encounters a high temperature above 900 °C, it will be directly carbonized to form a thermal insulation layer. These are not available in PE fiber protection products, and become the unique advantages of aramid products.
PE fibers are also used for armor protection of equipment. It was initially used in aviation equipment. In the late 1990s, this material was basically used for the protective armor of military aircraft developed by various countries. At present, all countries in the world have adopted a large number of PE fiber protective armor on ships, vehicles, armored vehicles and other equipment. The application of PE fiber armor in equipment solves the contradiction between weight and protection. Under the condition of limited weight, it better protects the safety of personnel, and improves the battlefield survival rate of equipment and personnel survival rate. Compared with metal armor, PE fiber armor is lighter in weight. Under the same protection level, the average weight can be reduced by more than half; in addition, there will be no ricochet secondary injury, and as the lining armor of steel armor, it can be very effective to prevent The inner layer of the steel armor caused by the shrapnel projectile collapsed, causing casualties.

During 2010, some scientists developed a "liquid body armor"
It weighs only two-thirds of normal body armor.
This liquid body armor uses a "shear-thickening fluid" that hardens when impacted by a bullet to block the bullet. It is actually a non-Newtonian fluid.
So what is a non-Newtonian fluid?
Non-Newtonian fluids refer to fluids that do not satisfy Newton's experimental law of viscosity, that is, fluids whose shear stress and shear strain rate are not linearly related. Non-Newtonian fluids exist widely in life, production and nature. The vast majority of biological fluids belong to what is now defined as non-Newtonian fluids. Various body fluids such as blood, lymph fluid, cyst fluid, and "semi-fluids" such as cytoplasm are all non-Newtonian fluids.
Also, a common food item like chewing gum is a non-Newtonian fluid.
The non-Newtonian fluid properties of shear thickening fluids are better.
If you stir slowly in it with your fingers, it's like a normal viscous liquid.
Scientists dipped traditional high-strength fiber body armor in a shear-thickening solution, and after many other processes, made our liquid body armor.

Left: ordinary body armor fiber                     Right: liquid body armor fiber

Left: Ordinary body armor                         Right: Liquid body armor
The new body armor is lighter. It originally required the strength of 15 layers of Kevlar body armor. After using shear thickening fluid, only 10 layers are needed to achieve the same effect, and the extra shear thickening fluid is more than that. 5 layers of Kevlar are much lighter.
However, despite the advantages of liquid body armor, the high cost, technical content, and mass production are still difficult, and it is difficult to fully promote it. However, it is believed that in the near future, the new liquid body armor will definitely become the most solid barrier to protect the safety of soldiers.