How does that work? Bullet Proofing
They save lives and are standard issue for police, armed forces and security guards all over the world. Body armour aims to minimise injury from projectiles fired from handguns and rifles. But how do they stop bullets that are travelling at speeds of more than 1000 kph?
It was the development of canons and guns that inspired the advance in armour technology. Traditional body armour could not get any thicker without making the wearer immobile, so the engineers turned to a new form of body armour to protect ourselves.
This falls into two categories - soft and hard body armour. The hard type consists of ceramic plates, which deflect the bullet. The ceramic used in body armour is not the same as is found in brittle ceramic bathroom tiles, but is a formula called alumina, Al2O3, which is very strong.
For soft body armour, interwoven pieces of clothing stop the bullets piercing the body. This might sound pretty strange, but it's similar to a football striking the back of a net at pace - the net threads pull on each other then on the goal posts, and the ball is stopped immediately. This absorbs the bullet, spreading its force over a larger area, causing it to buckle and stopping it before it can penetrate through to the body. The wearer still receives bruising or internal injuries from the force of the bullet's impact, but not as serious as a full on hit!
Most Kevlar vests consist of between 16 and 30 layers of woven Kevlar. These, however, should never be allowed to get wet - water acts as a lubricant allowing the bullet to slide between the fibres, although sealed panels within the vest can help improve the proofing.
The level of protection depends on the type of bullet and the type of armour. Vests can use various materials as the bullet stopper - steel, titanium, ceramic and polyethylene - usually between layers of Kevlar. Additional glass-fibre sheets can be added to protect against knife attacks as well; being able to protect against both high and low-velocity implements is something that not many fibres can do without providing a bulky, heavy armoured coat.
Bullet proof glass
To the casual observer, bullet-resistant glass looks the same as normal glass. However, normal glass shatters when hit whilst toughened bullet-resistant glass is able to withstand several rounds without buckling.
Bullet-resistant glass is made by sandwiching a polycarbonate material between two pieces of normal glass; the glass can be anything from 7 to 75 millimetres thick. When a bullet hits the glass, it smashes through the first piece of glass, but is stopped by the middle polycarbonate layer, which absorbs the bullet’s energy before it can pass out of the second piece of glass.
Bullet-resistant glass needs to be a lot thicker for a rifle than for a handgun. You can also get one-way bullet-resistant glass - in this case a brittle sheet of material is attached to a flexible piece of material. A person shooting at the glass hits the brittle side causing it to shatter but the flexible side then absorbs the energy. Meanwhile, on the other side of the glass, the bullet passes easily through the flexible material, onto the brittle one, which shatters allowing the bullet to escape.
The future?
Although Kevlar is the most commonly used fibre in body armour at the moment, there are alternatives being made all the time to stay ahead of the bullets. One such product is called Vectran, which is up to ten times stronger than steel, and twice as strong as Kevlar.
Spider’s silk is also being investigated, the chemical equivalent is called biosteel and is 20 times stronger than steel. Another future material is carbon nanotubes, which are even stronger than biosteel, although their expense will prevent their widespread use for the moment.
