Like any other material, it is not completely impenetrable. It is usually made from a combination of two or more types of glass, one hard and one soft. The softer layer makes the glass more elastic, so it can bend rather than shatter. The refractive indices of the two glasses used in the bulletproof layer must be nearly identical to keep the glass transparent and to obtain a clear, undistorted view through the glass. Bulletproof glass is available in thicknesses from 3⁄4 to 3+1⁄2 inches (19 to 89 mm).
Bulletproof glass is used in the windows of buildings that require this security, such as jewelry stores and embassies, as well as in the windows of military and private vehicles.
Bulletproof glass consists of layers of laminated glass. The more layers, the more protection the glass provides. Laminate 3mm polycarbonate (thermoplastic) to the safety side to prevent peeling when weight savings is required. The aim is to create a material that has the appearance and clarity of standard glass, but is effective against small arms. Polycarbonate designs typically consist of Armormax, Makroclear, Cyrolon, etc.: a soft coating that heals after being scratched (such as an elastic carbon-based polymer) or a hard coating that prevents scratching (such as a silicon-based polymer) thing).
The plastic in the laminate design is also resistant to physical impact from blunt and sharp objects. Plastic provides little ballistic resistance. Glass is much harder than plastic and can squash bullets, and the plastic deforms in order to absorb the remaining energy and prevent penetration. The ability of the polycarbonate layer to stop projectiles with varying energies is proportional to its thickness, bulletproof glass for this design may be up to 3.5 inches thick.
Laminated glass layers consist of glass sheets bonded to polyvinyl butyral, polyurethane, Sentryglas or ethylene vinyl acetate. Glass becomes stronger when treated with chemical processes. This design has been used regularly on combat vehicles since World War II. It is usually thick and usually very heavy.
Bullet-resistant materials are tested using a gun to fire a projectile from a set distance into the material, in a specific pattern. Levels of protection are based on the ability of the target to stop a specific type of projectile traveling at a specific speed. Experiments suggest that polycarbonate fails at lower velocities with regular shaped projectiles compared to irregular ones (like fragments), meaning that testing with regular shaped projectiles gives a conservative estimate of its resistance.When projectiles do not penetrate, the depth of the dent left by the impact can be measured and related to the projectile’s velocity and thickness of the material. Some researchers have developed mathematical models based on results of this kind of testing to help them design bulletproof glass to resist specific anticipated threats.
Well known standards for categorizing ballistic resistance include the following:
Summary of Euronational (EN) 1063 test conditions in English
Summary of Underwriter’s Laboratory (UL) ballistic resistance test conditions in English
U.S. National Institute of Justice (NIJ) standard resistant protective materials (NIJ Standard 0108.01).
The properties of bulletproof glass are affected by temperature and exposure to solvents or UV radiation (usually from sunlight). If the polycarbonate layer is located below the glass layer, it has some protection against UV radiation due to the glass and the adhesive layer. Over time, polycarbonate becomes more brittle, and because it is an amorphous polymer (which is necessary for transparency), it moves toward thermodynamic equilibrium.
At temperatures below -7 °C, the effect of pellets on polycarbonate sometimes produces flaking, and the polycarbonate fragments break and become pellets. Experiments have shown that the size of the spall is related to the thickness of the laminate rather than the size of the projectile. Spalling begins as a surface defect caused by bending of the inner polycarbonate layer, with the crack moving "backwards" to the impact surface. It has been suggested that the second inner layer of polycarbonate can effectively resist the penetration of exfoliation.
Bulletproof glass is often used in vehicle protection, shield windows, tanks, buildings, etc. It provides a guarantee for the safety of users to a certain extent. Compared with other bulletproof materials, bulletproof glass is heavier in weight and is not suitable for Individual combat, but its unique visibility is often used to make parts of some bulletproof products.