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Liquid Armor the New Bulletproof Vest
kjh1 writes "Armor Holdings Inc. plans to start selling their 'liquid armor' next year. The new armor, originally envisioned to be spread on like peanut butter, is instead sprayed onto Kevlar in ultrathin coats. From the article: 'it's a mix of polyethylene glycol, a polymer found in laxatives and other consumer products, and nanobits of silica, or purified sand. Together they produce a "sheer-thickening liquid" that stiffens instantly into a shield when hit hard by an object. It reverts to its liquid state just as fast when the energy from the projectile dissipates.'"
There's a video on break.com where you can see the liquid armor in action - it's pretty amazing:
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If the clothing is loose enough the knife/point object would still penetrate the skin, it just would be taking the fabric along for the ride.
I read awhile back (old wives tale maybe?) that being stabbed while wearing kevlar isn't always going to protect you as the knife does not have to penetrate the kevlar to penetrate the skin, especially cavity areas.
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This stuff sounds like a dilatant.
Kitchen experiment: take some cornflour and some water. Mix one part of water to about two parts of cornflour until you get a thick paste. Play with it.
If you apply gentle pressure, it behaves like a fluid. If you apply strong pressure, it abruptly solidifies. Scoop up a handful and throw it at something, and it'll bounce. Drop something heavy into a bucket of it and it'll sink.
Beach sand also manifests this behaviour, under certain situations; occasionally you can find a patch of heavily waterlogged sand that's rock hard when you walk across it, but if you stand still you slowly find yourself sinking in.
Disclaimer: cornflour almost certainly does not make good body armour.
Armor-piercing bullets tend to create less damaging wounds than soft bullets that are designed to expand upon impact and dump all of their energy quickly.
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The eggs one won't work, because the eggshell is rigid, and so provides no shear force on the coating. The trampoline one should work, but the effect you'd feel is negligible - this stuff works well at the speed of bullets, but at that small thickness you'd get little effect at the speed of a person's bounce. If you could get bubbles to work, then they'd still pop - they'd just pop slowly, since as the sides pull away from the initial point of zero thickness they'd cap their own speed.
Yeah, I did projects on this stuff. You can make some yourself with 1 part water and 1.44 parts cornflour; put it in at 1:1.3, then continue to add the rest of the flour while pouring. It'll get difficult to mix (don't do it in a machine, you'll break the machine, it's like stirring rocks at that speed) but a minute of perseverance will give you something you can bounce your thumb off or sink your finger in. Good fun. Kids love it, and it's easy to clean off; if it gets onto clothes then it just rinses out.
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Your example relies on a signficant difference in mass as well as overall rigidity of the two vehicles in question. Deformable frames being about absorbing energy (and momentum, being an inelastic collision) in an impact. An M1 brings way more Kinetic Energy to the impact than can be absorbed by a deforming frame of a Toyota.
The safety of the passengers is dependent on how quickly the vehicle passenger compartment decelerates, as that will determine with what force they impact the interior of the vehicle (the so-called "second impact"). The M1 will not decelerate very much, but it is because of the mass disparity, not that it is rigid.
Obviously a crumple zone cannot absorb an unlimited amount of energy, but up to the amount it can absorb it is definitely good for you, whether you are hitting something rigid or not.
Actually, this is not true. I've got some friends who do car safety analysis all the time and they say that a modern crumple zone + rigid passenger egg is safer than a rigid car or light truck in a collision - the crumple zone absorbs most of its car's energy and the rigid car flips over.
There are many dead SUV drivers to disprove your claim.
Except 3 rounds from a 45. planted square on his chest will either A: Knock him on his ass. B: Bruise his chest and wind him C: If your lucky pop his sternum D: All of the above Body armor just makes it so the round doesn't kill you. It still hurts like hell. Your body is still absorbing the energy of the round.
You mad
I've actually played with some of this stuff (I know the people who developed this, and by the way, there's no hyphen in Delaware, despite what BusinessWeek thinks) and yes, I don't see why they couldn't make butchers' gloves out of it. One of the easy demos they do is give you an ice pick and two pieces of kevlar and ask you to puncture each sheet. You can stab the ice pick through the normal kevlar but not through the shear-thickening fluid treated one. That should provide some protection against sudden knife slips that butchers might experience.
I became suspicious when I read the phrase "nano bits of silica". Nano technology my big toe: that's a marketing flourish.
The article mentions that this is a sheer thickening fluid, what they probably mean is shear thickening. That would be a fluid where the coefficient of viscosity increases with increasing strain rates, instead of remaining the classically Newtonian constant. In this case it's probably because the glycol tangles around the silica particles and can't untangle quickly.
While it's quite possible the material can become a semi-solid for the brief duration of a dynamic impact there is no reason to believe, and lots of reasons to not to believe, it becomes a particularly strong solid. In a particulate reinforced composite, which this is in its pseudo-solid state, the matrix (the ethylene glycol) is important to the strength and being a simple organic molecule it's strength must be on the same order of, say, polyethylene.
TFA itself infers this, noting the original idea of using the material itself (in peanut-butter mode) didn't work out. Instead it is employed as the matix in a conventional fiber composite using Kevar or Spectra or something like that as the workhorse.
As in all conventional fiber composites, the fiber bears the load, the matrix supports the fiber. In this case the support, I conjecture, amounts to preventing the fibers from displacing away from the impact point, probably allowing fewer layers of fiber to absorb a given impact energy.
Whle this is innovative and a good idea, it's hardly liquid armour. What I would hope for and maybe expect is better performance against pointy, hard, teflon-coated projectiles of the cop-killer variety which work by nosing the fibers out of the way.
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Larry Niven's Known Space series has armor exactly like this, that stiffens on impact. The only thing the armor has in common with Dune is that a slow impact gets through, IIRC in Dune they used some kind of force field. Larry describes what it's like to try to run in a suit like this while being peppered with automatic gunfire. Kinda funny. I don't think the Dune force fields stiffened up and made you fall over while being shot...
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Point #1: Momentum is a vector quantity. This means that a bullet approaching a person from the left and a bullet leaving said person, heading right, have totally different momentum vectors.
Point #2: In situations where outside forces can be ignored (such as a bullet impact), momentum is said to be "conserved". This means that any momentum change the bullet experiences has to be equal and opposite to the momentum change the person experiences. A bullet of mass "m" which is travelling to the right at speed "v" has momentum "mv" (taking the direction "right" to be positive). Similarly, the same bullet travelling to the left at speed "v" has momentum "-mv". Therefore, a bullet which ricochets off at its initial speed has TWICE the momentum change compared to a bullet which simply stops. As a result, the person has to experience double the momentum change as well.
This means that a ricochet imparts MORE momentum to the target than an embedded bullet would, which is (as another poster remarked) why solar sails are reflective.