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Military Develops Liquid Body Armor
kai5263499 writes "Military.com has an article about a new liquid body armor the U.S. Army Research Laboratory has developed. According to Dr. Eric Wetzel, the project coordinator: 'The key component of liquid armor is a shear thickening fluid. STF is composed of hard particles suspended in a liquid. The liquid, polyethylene glycol, is non-toxic, and can withstand a wide range of temperatures. Hard, nano-particles of silica are the other components of STF. This combination of flowable and hard components results in a material with unusual properties'."
"Polyethylene glycol (PEG) is a water-soluble, waxy solid that is used extensively in the cosmetic and toiletry industry."
c ol&sourceid=mozilla-search&start=0&start=0&ie=utf- 8&oe=utf-8
http://www.google.com/search?q=Polyethylene%20Gly
That's from the first link.
'Standards' in computing only impress those who are impressed by things like 'standards'.
its resistance to stabbing has to be called into question
According to the article: "Liquid armor is much more stab resistant than conventional body armor. This capability is especially important for prison guards, who are most often attacked with handmade sharp weapons."
"poly" changes it completely. Binyl chloride is pretty nasty (much much worse than ethylene glycol), but polyvinyl chloride is PVC and that's all over the place. Generally when you polymerize a monomer you are using up the reactive sites that would normally cause toxicity to form bonds with other monomer molecules. The same thing goes for a whole lot of other monomers.
Polyethylene glycol is actually really bio-friendly. Proteins don't stick to it well so it can be used in the body. You can even eat the stuff. I can't think of specific products, but I know it's on the ingredient label of lots of things we eat.
Ethylene Glycol: C2H6O2
Polyethylene Glycol: C2H4O
So they are pretty different from a chemical standpoint. Good old Ethylene Glycol melts at -13C, while the "poly" melts at 60C. However, when looking up an MSDS on this stuff, I get "May act as an irritant. Toxicology not fully investigated" so I wonder about it being completely non-toxic.
See link here.
Yes, this is the same type of process. Fluid when handled gently, but it becomes rigid when subjected to a sharp impact.
If you jab it, it feels hard and your finger won't go in very far. You can pour it slowly, but you can grab a clump of it, almost as if it's a solid. This kind of fluid is called dilatant. It becomes more viscous when agitated or compressed.
The cornstarch mixture is sometime called ooblick.
Does the "poly" really change it all that much?
In a word, yes. Here are the Material Safety Data Sheets for both chemicals:
ethylene glycol
polyethylene glycol
I like my beverages with warning labels!
For a scientific paper on the subject, see Advanced Body Armor Utilizing Shear Thickening Fluids, by Y. S. Lee, R. G. Egres Jr. and N. J. Wagner, all of the Center for Composite Materials and Dept. of Chemical Engineering, U. of Delaware, and E. D. Wetzel of the Army Research Laboratory, Weapons and Materials Research Directorate Aberdeen Proving Ground.
For a University of Delaware Press Release (with photos), see here.
Only Women Bleed (Sex, Sharia remix)
This is straight off of Army News Service.
And they even have a picture!
HO-CH2-CH2-OH
The repeat unit of polyethylene glycol looks like this:
-CH2-CH2-O-
So with polyethylene glycol, just attach that unit end-to-end over and over again. How many repeat units you have in the polymer will determine the melting point and many other properties. The MSDS you link to is for PEG-8000, which probably means it has a molecular weight of 8000.
Incidentally, you'll notice that the ethylene glycol unit (the monomer) is different from the PEG repeat unit by an H2O -- water is a byproduct of the polymerization.
Polymerization does make a huge difference in properties. Polyethylene is basically ethane (or, if you look at it another way, methane) attached end-to-end, but polyethylene, of course, is very different chemically from methane.
Finally, I get to post to Slashdot about a technical subject I know something about. Quick, someone, mod me up! It may never happen again! :)
Actually, no, it doesn't.
(Very) brief lesson in fluid dynamics.. Newtonian fluids obey this "law:"
Shear stress = - viscosity * shear rate.
Imagine you have two panes of glass. You lay one out horizontally and pour a layer of liquid on to it (we'll pretend it stays on and doesn't run off onto the floor). Then you place the second pane of glass on top. You apply a constant, horizontal force to the top pane of glass, and it begins to move at a certain velocity.
shear stress = the force * the area of the glass
shear rate = the velocity / the distance between the two panes (not really, but close enough for our example)
Fluids with viscosities that don't depend on the shear rate are called Newtonian. Water is largely a Newtonian fluid. It's viscosity depends very strongly on temperature, but not much on shear rate. Doubling the shrear stress (the force) would result in a doubling of the shear rate.
Ketchup is a good example of a non-newtonian shear-thinning fluid. If you put ketchup between your glass panes, you'd find that smaller and smaller amounts of additional shear stress are necessary to increase the shear rate by equal amounts. This is easy to understand, b/c our everday experience with ketchup tells us that it can take a big shock to get it moving, but once it goes, it goes quickly. (The viscosity is high at low shear rates, like when it isn't moving, and so a lot of shear stress is required. Once it starts, the shear rate goes up, the viscosity decreases, and less shear stress is needed).
The fluid in these vests is the opposite of ketchup. It is shear-thickening. At the shear rates the armor is subjected to in ordinary movement, its viscosity presumably remains low, allowing the soldier to move. But when someone tries to stab through it (a fast, high shear movement) it thickens (its viscosity increases) and the blade/bullet/whatever is stopped.
I don't know how the stuff is sewn, but it could be sewn slowly without a problem. Remember, it's shear rate that makes it thicken up.