Half a croissant, on a plate, with a sign in front of it saying '50c'
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Smart Vest

It hits the right spot.
  [vote for,

I have recently been conducting an at-home study of Shape Memory Alloys, and have come to know thier various properties fairly well. These materials are metals (usually nickel titanium alloy) that are elastic, but can "remember" a shape and will return to it given a certain temperature, or sometimes an electrical current. A 20cm, hair-thin strand can lift up to 25 times it's own wait, and contract up to 8% (a few contracted to 10% with no problem that I have encountered). My thought is that perhaps slightly tougher bands could be sewn into a keval vest, forming a mesh both horizontally and vertically. They would form a network which would compress with enough heat, and bunch the fabric together to put more between the bullet and the person.
Paine, Jan 30 2003


       Kevlar vest, that is.
Paine, Jan 30 2003

       Isn't Troy Hurtubise working on something lkike this for his bear-proof suit?
oneoffdave, Jan 31 2003

       How fast do the strands react ?   

       It depends on the type of bullet you're protecting agains, too. Most "flak vests" are intended to protect against relatively low velocity rounds from handguns; the projectiles have a blunt profile to the tip, and are perhaps only half-jacketed whereas smaller-calibre full-metal-jacket rounds from assault rifles and up then to have a much sharper point. They are intended to cause damage and injury through different energy-transfer mechanisms.   

       You need to consider what the vest is intended to protect against. I presume that your're intending that the projectile would heat the vest structure as it enters, causing the Nitinol strands to realign and generating the "bunching" effect you describe.   

       Consider a typical 9mm parabellum round, which (purely for the sake of argument) we will assume has a typical muzzle velocity of 350 metres per second. This is an approximate figure only and will vary widely depending on the ammunition and the weapon. At short range, the impact velocity will, for all practical purposes, be the same as the muzzle velocity.   

       With a vest that is, at the most, 20mm thick, the time for the projectile to cover this distance is only 57 microseconds. If the system is "reactive", the available reaction time is perilously short.
8th of 7, Jan 31 2003

       Yet another reason why you should wear a barrel filled with water.
thumbwax, Jan 31 2003

       Doesn't everyone ?
8th of 7, Jan 31 2003

       I like the barrel filled with water Idea. It would get rid of the Hyperthermia risk in the summer. Then you wouldn't need your camel pak, just a straw.   

       I agree with [8th of 7] "Action is faster than reaction."
SunTzu, Apr 30 2003

       Use custard.
k_sra, Apr 30 2003


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