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A series of newb questions

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: Natex88 » Sat Apr 12, 2008 5:57 pm

On the topic of the Kevlar, I went and found someone who talked about its strength, and this is what they said:

Bulletproof vests are designed to stop BULLETS not knives. It might take a little bit more force to stab through one, but its not really that hard. Bulletproof vests are actually quite malleable, and are made up of multiple layers of fabric and kevlar -- they help minimize the impact of a bullet by distributing its impact over a larger area. And, a key component that is instrumental is the design of kevlar is that the object must be traveling at an extremely high velocity. A blade can go right through a bulletproof vest because it was not designed or meant to protect against that kind of a weapon. They actually make stab proof vests ... they work a completely different way.

Edit: "Bulletproof Vest" is also somewhat of a misnomer ... they cannot offer 100% protection against bullets. Regardless of whether or not the vest actually succeeds in stopping the bullet you are going to be injured. It would be kind of like being hit with a frozen paint ball -- it will leave bruises, and can even break bones. Furthermore, the police version of a bulletproof vest your average beat officer wears is not designed to offer relative protection from rifled ammunition, nor from point-blank handgun rounds (especially higher caliber rounds). Military combat body armor is much different from that Police Officers wear ... it is designed to protect against rifled ammunition.

Source: http://answers.yahoo.com/question/index?qid=20080408135020AAGp87E

So it seems that it doesn't do too well with knives at least, not like you'd expect. It might be better with PVC, but I don't really want to find out :P
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Unread postAuthor: DYI » Sat Apr 12, 2008 6:11 pm

That's interesting, because PVC shards leaving the failure point would be somewhere in between bullets and knives. I'd lean more towards the "bullet" side, because they were fired with a set amount of energy, and no more energy is applied after that.

Still, the operation of a Kevlar vest relies on there being something soft underneath it; if you stretch one over a frame, bullets from small weapons will pass right through.

The real solution to this problem is not to prevent existing shrapnel from leaving the enclosure, but to prevent the creation of accelerated shards to start with, and I believe that a tight and thick enough wrap of carbon fiber or fiberglass, while it may not actually prevent failure, would hold together the pieces of a pipe that experienced a catastrophic failure.
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