Slashdot Mirror
Polyethylene Bulletproof Vests Better Than Kevlar
teflonscout writes "When I think of bulletproof vests, the first word that comes to mind is Kevlar. Wired is running a story on Dynema SB61, a bulletproof material that is made of polyethylene. It is a higher grade of the plastic found in Tupperware. The story also mentions the recall of Second Chance bulletproof vests that were made from Zylon, a material that degraded slowly when exposed to moisture. At least one police officer was injured when a bullet penetrated his Zylon vest. Polyethylene is impervious to moisture. The first vests made from this new material are 5mm thick and can stop a 9mm bullet traveling at 1777 feet per second, which is slightly better than other top of the line vests."
Can't wait to see The Box O' Truth give it a try.
Or you could just get some Dragon Skin armor that will take the force of an exploding hand grenade and not allow penetration...
i n.php
http://www.pinnaclearmor.com/body-armor/dragon-sk
Mr. McGuire: I want to say one word to you. Just one word.
Benjamin: Yes, sir.
Mr. McGuire: Are you listening?
Benjamin: Yes, I am.
Mr. McGuire: Plastics
the density of Kevlar is 1.44, while polyethylene is 66% as dense at around 0.94 to 0.96, will actually float in water.
Most current suits of body armor can stop a pistol caliber bullet. Rounds designed to pierce armor, or designed to be fired from a more powerful gun, are another story. Armor that will stop a small, soft bullet will still be penetrated by a faster, or less malleable one.
For civilian or police protection, we have nearly impenetrable suits now; increasing their coverage, or decreasing their weight would be more practical (both of which can be achieved by making them out of lighter materials). For something like military protection, well, we may never have impenetrable body armor. Whenever defensive technology gets good enough, the military turns their attention to piercing those defenses; see for example the death of the battleship as a viable class of warship.
Apart from that, conservation of momentum applies. There is an upper limit whereby body armor would remain intact, while the flesh beneath is reduced to a pulp. Though admittedly conservation of momentum also applies to the shooter, and to the recoil of their gun, so there is a similar upper limit for muzzle velocity per unit of projectile mass.
Erotic is when you use a feather. Exotic is when you use the whole chicken.
1) You are equating weight with stopping power for different materials. That is an incorrect comparison. That might make sense when comparing two vests of the same material and design. Vest A has 10 lbs of Kevlar, Vest B has 20 lbs Kevlar. Both vests are of similar designs and Vest B should be better at stopping bullets. However if another company designed a different type vest (Vest C) with Kevlar that had better stopping power but only used 10 lbs Kevlar, the use of weight alone in comparing effectiveness would not be valid.
2) Body armor is heavy, especially considering all the other gear a soldier has to carry. If body armor was lighter and provided the same amount of protection, many soldiers would prefer it.
Well, there's spam egg sausage and spam, that's not got much spam in it.
Best part is that most "saves" the vests are credited with are from car accidents, where the vest acted as extra support, etc. for the spine and whatnot....
Don't blame me, I voted for Kodos
Soft body armor is designed to defeat handgun bullets, which is why it is so useful for police. Hard body armor is much bulkier but is designed to defeat rifle rounds. In general, a rifle round is significantly more powerful than handgun rounds.
This is one of those cases where allegory is truly misleading. The article makes the comparison to shopping bags and tupperware in order to emphasize the "everyday" nature of the material. The truth is that they have similar basic components, but the exact composition and processing differences cause one material to be good at resisting bullets and another at storing food (or selling at parties.) Unlike Tupperware, Dyneema vests are composed of woven and laminated fabric.
Dyneema is actually a trade name for a thread derived from Ultra High Molecular Weight polyethylene. The intrinsic strength of the material comes from the ability to increase the length of the polyethylene chain to extreme lengths. Since the structure of UHMW derives its strength mostly from the intermolecular Van-der Waals forces, the longer the polythethylene chains get, the stronger the forces holding the material together become. When the processing of the polythylene allows the length of the chains to become uniform, then you can engineer it into useful forms, such as a fiber which eventually be formed into fabric, then laminated and put on your chest.
Of course, being UHMW, Dyneema has a weakness: Its melting point is about 300 degrees Fahrenheit, or about the temperature of a hot light bulb. Which means that while your body heat might not harm the vest, carelessness in storage might.
Independent tests do not support the army's conclusions. Since there is already some question about the validity of the army's tests (e.g. the designer of the vest that "won" in the army's test says that dragon skin is actually better, the person who conducted the army tests left to work for a dragon skin competitor, etc.) I don't think just repeating the army's conclusions (or quoting the Washington Compost as doing so) really proves anything.
--MarkusQ
As with anything, the devil's in the details. From a previous trip around the web in re: bodyarmor.
It's not Tupperware, but 'Ultra high molecular weight polyethylene'.
See also:
Spectra
Dyneema
Aramids (from "aromatic polyamide")
- Example: Twaron
Kevlar, of course.
Also Nomex - known for it's heat-resistant attributes, also strong. It's an "aromatic nylon, the meta variant of the para-aramid Kevlar."
The low melting point is also not good in combat situations.
Its highly recommended to wear *cotton* and not nylon clothes, for example, because cotton won't melt to your skin if you survive an IED attack.
-- My Sig is a P228.
Strictly speaking, rifles are small arms. Generally, "small arms" is a term that encompasses anything a soldier can fire unsupported.
Reality has a conservative bias: it conserves mass, energy, momentum...
I'm from the small town in Michigan in which second chance was founded, and I know the entire history of the "incident"
The officer in that shooting was shot 6 or 7 times. *ONE* bullet penetrated the Zylon, and it was on the periphery of the vest. The edges of *ANY* vest are vulnerable and not as strong as center-mass.
Second chance has 960+ confirmed saves with their body armor.
What they've done to the second chance business as a result is, on the whole, a travesty. They were/are one of the few american manufacturers, and they did nothing wrong at all.
I've been using polyethylene armor on my fighting robots for years. It's extremely tough, lightweight, and relatively cheap. There was a fashion for using polycarbonate (Lexan) on fighting robots for a while, and while it looks cool (it's clear), it just can't take impact like UHMW polyethylene.
Your design to a real part online: Big Blue Saw