Construction
Bullet-resistant glass is usually constructed using polycarbonate, thermoplastic, and layers of laminated glass. The aim is to make a material with the appearance and clarity of standard glass but with effective protection from small arms. Polycarbonate designs usually consist of products such as Armormax, Makroclear, Cyrolon, Lexan or Tuffak, which are often sandwiched between layers of regular glass. The ability of a glass itself to withstand shock is improved by the process of tempering. When treated with heating and cooling or with chemical processes, the glass becomes much stronger. The polycarbonate usually has one of two types of coating to resist abrasion: a soft coating that heals after being scratched (such as elastomeric carbon-based polymers) or a hard coating that prevents scratching (such as silicon-based polymers) it can break or cracked after a couple times of it being shot. The plastic in laminate designs also provides resistance to impact from physical assault from hammers, axes, clubs,crow bars and so forth. The plastic provides little in the way of bullet-resistance. The glass, which is much harder than plastic, flattens the bullet, and the plastic deforms, (hopefully) absorbing the rest of the energy and preventing penetration. The ability of the polycarbonate layer to stop projectiles with varying energy is directly proportional to its thickness, and bulletproof glass of this design may be up to three inches thick.
Laminated glass layers are built from glass sheets bonded together with polyvinyl butyral, polyurethane or ethylene-vinyl acetate. This design has been in regular use on combat vehicles since World War II; it is typically thick and is usually extremely heavy., it can break after being shot at 2 times
Sample thickness and areal densities for bullet-resistant glass materials | |||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
NIJ | Threat Stopped | Glass Laminate | Polycarbonate | Acrylic | Glass-Clad Polycarbonate | ||||||||||||
Protection Level | (example) | Thickness | Density | Thickness | Density | Thickness | Density | Thickness | Density | ||||||||
in. | cm | lb/sq. ft. | kg/m2 | in. | cm | lb/sq. ft. | kg/m2 | in. | cm | lb/sq. ft. | kg/m2 | in. | cm | lb/sq. ft. | kg/m2 | ||
I | 9 mm | 1.185 | 3.009 | 15.25 | 74.46 | 0.75 | 1.905 | 4.6 | 22.46 | 1.25 | 3.175 | 7.7 | 37.6 | 0.818 | 2.078 | 8.99 | 43.9 |
II | .357 Magnum | 1.4 | 3.556 | 17.94 | 87.6 | 1.03 | 2.616 | 6.4 | 31.25 | 1.375 | 3.492 | 8.5 | 41.50 | 1.075 | 2.73 | 11.68 | 57.02 |
III | .44 Magnum | 1.59 | 4.038 | 20.94 | 102.24 | 1.25 | 3.175 | 7.7 | 37.6 | 1.288 | 3.271 | 14.23 | 69.47 | ||||
IV | .30 Caliber | 1.338 | 3.525 | 14.43 | 69.47 | ||||||||||||
V | .30 Caliber | 1.338 | 3.525 | 14.43 | 69.47 | ||||||||||||
VI | |||||||||||||||||
VII | |||||||||||||||||
VIII | 7.62 mm | 2.374 | 6.03 | 26.01 | 126.99 |
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