Liquid armor

[Dr Mordrid]

STF's (shear thickening fluids; like Silly Putty or cornstarch + water);

http://www.dcmilitary.com/army/pentagram/9_17/national_news/28729-1.html

Dr. Mordrid

[ZokesPro]

That kicks ass!

[Kruzin]

It's just mind-boggling that they can make something that reacts fast enough to counter a gunshot or even something much slower, like shrapnel, in the form of a fabric.

[agallag]

If you want a simple demonstration of how this stuff works, try the Doc's combination of cornstarch and water. Just get a little bowl, pour in a bit of cornstarch, then add water until it's mostly dissolved.

Stir very slowly with your finger, and it'll feel just like water. No resistance at all. Move your finger quickly, and it gets instantly thick, almost solid. As soon as you release the pressure on your finger, and go back to moving it slowly, it's completely back to liquid. It's a really cool effect. I can play with the stuff for hours on end

[Kruzin]

I can think of things I'd rather stick my finger in and twirl about than a bowl of water and starch.

[RC Agent]

Oh my!

[Dr Mordrid]

I'm with Kruzin, but I'd use more than one finger and do a lot more than twirl them around

Dr. Mordrid

[Kruzin]

Yea, like home-made from scratch cake batter for a nice chocolate cake...or egg whites for a lovely lemon merangue pie....

[Jammrock]

Sounds a lot like a tank armor I saw a while back. They sandwiched a granual-like black substance between two armor plates. After a projectile penetrated the first plate and reached the granual substance, the heat expansion and sheer tight packing of the granuals caused the projectile to slow and stop via side pressure. Even if the projectile was explosive, the granuals would absorb most of the explosion, leaving the under armor virtually untouched.

This seem like a lighter liquid version of the same concept.

Jammrock

[Jon P. Inghram]

That'd be great for a glove, comfy and soft most of the time, but hits like hard plastic when you punch someone!

[Dr Mordrid]

Nice replacement for Gor-Tex

Dr. Mordrid

[Jon P. Inghram]

For a more positive civilian use (I suppose "magicly" hardening cloth knuckles arn't very nice, ) you could combine that stuff with magnetorheological fluids to make sports gear that could protect from sudden impacts and falls by hardening around joints electronicly and spreading the impact forces with the STF's.

I wonder what this could do for tires or shock absorbsion systems? Cool stuff...

[jms]

Originally posted by Jammrock
Sounds a lot like a tank armor I saw a while back. They sandwiched a granual-like black substance between two armor plates.

Yeah, that is actually explosives they sandwich between the armor plates. It is called Explosive Reactive Armor.

[Brian Ellis]

For a practical every-day situation, just step onto very wet sand. The sand compacts to support your weight, as the water forms a film above it.

I'm rather surprised at the mention of ethylene glycol as the fluid. It would have to be a polymerised EG to hold the particles in suspension and PEGs tend to have the opposite effect, thixotropy, such as used in "non-drip" paints, etc. Perhaps, on reflection, this is the secret: the liquid becomes less viscous on shear, allowing it to squeeze out more rapidly from the particular matter, which does the work.

I have a more general question: the kinetic energy of a 25 g bullet travelling at, say, 500 m/s is not negligible. If this bullet is stopped by a flak jacket or whatever, the 2nd law of thermodynamics tells me that this energy must be converted to heat. Does the person wearing the jacket suffer from burns?

[Dr Mordrid]

Much of the energy would be distributed as a shockwave radiating throughout the jackets fluid as it compresses, eventually becoming heat but spread over most of the jackets surface area.

Much of the rest would be absorbed in the usual Kevlar way: stretching the fabric matrix plus leaving one helluva bruise on the wearer.

BTW:

The 25 grain bullet at 500 meters/s you mentioned is slightly more powerful than a .22 long rifle with a hot load. They're often used to hunt squirrels, marmots and rabbits but it's not much on larger game or humans absent a head shot. Even lightweight armor makes mincemeat of them.

M-16's use a 62 grain .223 caliber (5.56 mm) bullet jacketed in brass, travels at ~1000 meters/s and tumbles after it penetrates. Devastating without body armor.

AK-47's use a 122 grain 7.62mm bullet traveling at about 730 meters/sec.

By comparison the most popular American deer rifles are the 30-30 and the 30-06.

The 30-30 is most often in the form of a Winchester 94 (or similar) like those seen in westerns or a semi-automatic carbine (short barreled). It can fire a 150-170 grain bullet traveling up to 700 meters/sec. Not as fast as the AK-47, but more powerful due to the heavier bullet.

The 30-06 is the most popular deer hunting rifle in North America. It fires a 125-220 grain bullet at up to 1000 meters/sec. Their impact can be devalstaing even on large game at long ranges.

30-06's are also extremely accurate. With a target rifle and ammo one can hit a grapefruit at 1000+ meters. At 100 meters with a good hunting rifle any decent shooter can put at least 6 of 10 shots into a 3 cm hole.

Dr. Mordrid