Bulletproof Glass Information

Bullet-resistant glass (colloquially known as bulletproof glass) is a type of strong but optically transparent material that is particularly resistant to being penetrated when struck by bullets. It is also known as transparent armour.

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 plastic in laminate designs provides resistance to impact from physical assault from hammers, axes, clubs, and so forth. The plastic provides little in the way of bullet-resistance. The glass, which is much harder than plastic, flattens the bullet, which prevents penetration. This type of bullet-resistant glass is usually 70–75 millimetres (2.8–3.0 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 100–120 millimetres (3.9–4.7 inches) thick and is usually extremely heavy.

One-way

Advances in bullet-resistant glass have led to the invention of one-way bulletproof glass, such as used in some bank armored cars. This glass resists incoming small arms fire striking the outside, but will allow those on the other side, such as guards inside the vehicle, to fire out through the glass at the exterior threat.

One-way bulletproof glass is usually made up of two layers, a brittle layer on the outside and a flexible one on the inside. A bullet fired from the outside hits the brittle layer first, shattering an area of it. This absorbs some of the bullet's kinetic energy, and spreads it on a larger area. When the slowed bullet hits the flexible layer, it is stopped. However, when a bullet is fired from the inside, it hits the flexible layer first. The bullet penetrates the flexible layer because its energy is focused on a smaller area; the brittle layer then shatters outward due to the flexing of the inner layer and does not significantly hinder the bullet's progress.

The ability of a glass 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.

"One-way" bullet-resistant glass is far from being perfected; there is evidence that shows it can be achieved, but in most cases when shooting from the "safe-side", the intended target would have to be very close for the bullet to cause lethal wounds.

Recent advances

U.S. military researchers are developing a new class of transparent armour incorporating aluminium oxynitride (Trade name: ALON) as the outside "strike plate" layer. It is much lighter and performs much better than traditional glass/polymer laminates. Aluminium oxynitride "glass" can defeat threats like the .50 caliber armor piercing rounds using material that is not prohibitively heavy.^[1] Various types of other materials which closely resemble glass are also being developed.

Spinel Ceramics

Certain types of ceramic Spinel (a class of mineral) can also be used for transparent armor due to their properties of increased density and hardness when compared to traditional glass. These new types of synthetic ceramic transparent armors can allow for thinner armor with equivalent stopping power to traditional laminated glass.^[2]

See also

• Transparent Armor Gun Shield (TAGS)
• Prince Rupert's Drops
• Access control vestibule

References

1. ^ Air Force testing new transparent armor Laura Lundin, Air Force Research Laboratory Public Affairs. October 17, 2005. Last accessed November 9, 2006.
2. ^ http://bulletin.accurateshooter.com/2010/05/ceramic-transparent-armor-may-replace-bullet-proof-glass

Categories: Glass coating and surface modification | Armour

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