How does Bulletproof made of Check the Article From TamilYoungsters.com

The three men fi re more than 250 shots at the limousine. It’s not only handguns that are unleashing deadly payloads at the Audi A8: modern assault rifl es are showering the car with bullets. Some of the projectiles strike the car’s window pane – already showing thousands of cracks – at speeds of 800 metres per second, twice as fast as a bullet fi red from a revolver. Next, two grenades explode on the limo’s bonnet, and 10kg of TNT detonate beneath its chassis. The force of the explosion launches the four-tonne vehicle into the air. But this vault-on-wheels does not rupture under the ferocious barrage, and its occupants sustain only minor injuries… What appears to be a terrorist attack is actually a test undertaken by a ballistics testing centre. The culprits are civil servants; the occupants are dummies. The car is a special armoured protection vehicle worth more than $800,000. From the outside it looks like a standard-issue model, but under the paint there is completely new technology at work. Almost every inch is covered with steel armour. And to ensure that this hefty limousine is still capable of speeding off in the event of an attack, all of its components, from the chassis to the motor, have their weights adjusted. The car’s windows are particularly vulnerable points, as it’s behind them that the targets of any would-be attackers can be found. The glass, then, must be capable of resisting the most powerful bombs and weapons. So how does it manage that? Well, for a material often thought of as fragile, glass is actually very hard (see left). However, it does possess one major defect: although a window pane feels smooth to the touch, there are actually billions of microscopic cracks across its surface. When suffi cient pressure is applied – a hard knock, for example – one of the cracks will spread, leading to breakage. In order to make glass stronger, then, these cracks need to be pressed together. There are two methods for achieving this: using heat, or using chemicals. With chemical hardening – which is used with very thin glass – the pane is immersed in a sodium nitrate bath for several hours, pushing smaller particles at the surface downwards and replacing them with larger ones, which require more space. The resulting tightness causes the surface to push against the inside of the glass, which seals any existing cracks together. Thermal hardening is used on glass that’s about four millimetres thick. A pane is heated then quickly cooled, which causes the outer layers to immediately
solidify while the interior remains soft. As a result of the temperature difference, the atomic structure is distorted, and the glass stretches like a spring and presses the cracks together. For glass to be bullet-proof, however, a single hardened pane is not enough, and so numerous panes are combined with layers of plastics such as polyvinyl butyral and polycarbonate – the latter being the type of plastic from which CDs, helmets and many mobile phone casings are made. The materials make the glass composite elastic, and bind any fragments resulting from impact. This creates a near-impenetrable shield against bullets. The more panes that are joined together in this way, the harder it is to break through. The panes of a high-security vehicle can be up to 72 millimetres thick; on a normal car, it’s four millimetres. But even this doesn’t guarantee safety, says Phil Brown from glass manufacturer Pilkington: “We tend to shy away from claiming glass to be bullet-proof. ‘Proof’ suggests it will defi nitely stop anything fi red at it.”