Naked Science Forum
Non Life Sciences => Technology => Topic started by: paul.fr on 03/08/2007 16:35:48
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Is it just the fact that there are many layers of glass or it it actually some chemical composit or what?
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One has to understand what you mean by "strong".
Although not pertinent to bullet proof glass, but more to bullet proof vests, but some bullet proof vests have been very effective at stopping a bullet, but will not stop a knife (more modern bullet proof vests are typically also knife proof - but it is to emphasise that it is not so much raw "strength" that is the issue, as understanding the precise nature of the force you are trying to stop).
You have to recognise that bullet proof glass is not normally designed to stop heavy artillery projectiles, but rather to merely stop projectiles from hand held weapons (even if from a long barrel rifle, that rifle is still held by a person, and unlikely to be mounted on a heavy truck). This means that energy of the projectile cannot be greater than that which the man holding the weapon is able to withstand the recoil from.
The point is that the man holding the gun feel the recoil through the width of the stock of the weapon, and so that energy is spread out; whereas the man feeling the bullet hit him, feels the energy concentrated in the narrow tip of the bullet. The purpose of bullet proofing is the be able to spread that energy out without tearing (in the case of the fabric of bullet proof vests) and without shattering (in the case of bullet proof glass).
Traditionally, bullet proof glass (which used to be very heavy) was indeed made of many layers, so that even if the outer layer were to shatter, that would not penetrate through to the lower layers. Modern bullet proof glass is in fact plastic (typically polycarbonate - the same stuff that safety spectacles, and the roofing for conservatories, is made from).
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I posted this is gen.sci, but is it just the fact that there are many layers of glass or it it actually some chemical composit or what?
To make shock-resistance glass: the hot sheet of glass is colded very fast on its outer surfaces with strong jets of cold air; in this way the outer dimensions are blocked before the central part of the glass cools and this generate very strong elastic tensions inside when it cools completely; imagine the hot glass inside that tries to shrink when it cools but it can't because it's attached to fixed positions: it behaves as strong springs oustretched inside.
This gives its final resistance.
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Bullet proof glass usually consists of several layers of glass laminated with thick layers of soft resilient clear plastic this makes the energy absorbtion capability much greater than a single thick sheet of glass or plastic.
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Bullet proof glass usually consists of several layers of glass laminated with thick layers of soft resilient clear plastic this makes the energy absorbtion capability much greater than a single thick sheet of glass or plastic.
Yes, they use alternate glass/policarbonate layers packed tightly.
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Bullet proof glass usually consists of several layers of glass laminated with thick layers of soft resilient clear plastic this makes the energy absorbtion capability much greater than a single thick sheet of glass or plastic.
Yes, they use alternate glass/policarbonate layers packed tightly.
I knew that too [^]
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Nothing is bullet "proof". Just resistant. High-powered rifles and close range (point blank) can still penatrate.
But America's doing it's best. Ever see Future Weapons? Dragon Skin is an armor impervious to artillery shells. So while your arms legs and head get blown off, you chest will be just fine.
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I liked the glass that lets bullets through one way easier than the other. Plastic on the inside and glass on the outside. A bullet arriving on the outside breaks the glass and compresses it into a wide ' plug' as the plastic flexes. This produces a relatively low stress on the plastic; the bullet stops.
From the inside, a bullet penetrates the inner plastic (higher pressure) and then bursts through the outer glass which shatters and spreads out in all directions.
Just not fair on the attacker.
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Nothing is bullet "proof". Just resistant. High-powered rifles and close range (point blank) can still penatrate.
But America's doing it's best. Ever see Future Weapons? Dragon Skin is an armor impervious to artillery shells. So while your arms legs and head get blown off, you chest will be just fine.
A couple of years ago, at our town's police/fire company open house day, I tried on the SWAT team's bullet-proof vest. It was really heavy, like wearing a brick coat. Before I always thought our technological advances in materials science had enabled us to produce light-weight body armor. Now, I know better. This also explains why bullet-proof vests are vests, and don't cover your arms and legs, because if they did, you wouldn't be able to lift the gun or run at all.
I wonder if there're any new bullet-proof vests made of really light yet strong material? If so, how light are they?
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I think it depends on what you are trying to stop. Stopping a handgun round from a reasonable distance can be done quite easily and makes for quite a lightweight vest, but if you want to stop a supersonic high velocity rifle round, you have a lot more energy to dissipate in a much smaller area, so you have to try a lot harder. There are designs for ceramic plate body armour's such as one I was reading about called dragonskin (http://www.pinnaclearmor.com/dragon-skin-survivors.php) this has little discs of ceramic, which are destroyed by the impact of a bullet, but they stop it and distribute the impact. It is supposed to be lighter and more flexible than the more conventional equivalent. They have been having issues selling it to the US army as it is expensive, but they have apparently been successful in selling kneepads, as there have been a lot of people incapacitated by knee damage from IEDs.
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IEDs? What are they?
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improvised explosive device
boom boom!
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there is a potential space between each layer of glass which has vaccum in it making the glass bullet proof.
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Why would that work?
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its the same mechanism that is used to design space rockets walls. Actually this breaks the velocity of the bullet and drops it rapidly as the bullet changes the medium by first hiting the glass then entering the vaccum layer which gives the bullet a blow as air enters it then again it happens so hardly the bullet goes by the 3rd layer and different number of layers are available depending upon the requirement.
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If there's a vacuum ahead of the bullet and air behind it the bullet will be accelerated, not stopped.
Also, if you had a window with a vacuum chamber inside it, you would need some way to stand the several tons of pressure from the atmosphere trying to squeeze the glass panes togther. If they were strong enough to stand that, I don't think a bullet would go through them anyway.
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Bulletproof glass can also be made of acrylic. There are level 1 - 8 which are different thicknesses making them stronger.
Mod edit - link removed
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There is a synthetic one called "Lexigard" came out about the 80's 90's,
Its similar to perspex but stops high powered rifle point tip solids.
Look up US manufacturers, there may be old technology info available
in chemistry.
For the point of mention/here-say, the US has had grades of glass for decades that are considered to be as good for vehicles as small cannon
e.g. .50 calibre military machine gun.
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Hi man,
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So thank you
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All said and done, how many different ways can one make a glass bullet-proof?
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Get thin layers of polyvinyl butyral (PVB), sandwich them between sheets of standard glass, and bonded together by heat. Alternating layers of plastic and glass are then built up. The more layers, the better the bullet-stopping power.
http://www.guardian.co.uk/science/2004/feb/19/thisweekssciencequestions3
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As well remember that the glass uses different thicknesses of glass, the initial outer layer is thin, then bonded to many thinner layers. The final layer is thick glass, with a polycarbonate layer on the outside. This will absorb energy to shatter the glass layers, but will not fail to the point where a bullet can penetrate. The bad problem with bullet resistant glass is that it can really only be made in flat sections, unless the application is high enough volume or cost to make the multiple molds to bend the glass layers worthwhile. It can only be cut with a diamond tipped saw, well lubricated with water.