It depends on the gun, but 1000 feet per second is a good number to start with. Given that speed, we’re looking at one foot in a millisecond.
That’s gonna take a lot of silly putty.
The stiffening occurs by a physical jamming mechanism which depends on deformation of the material. The faster the deformation, the faster the material stiffens. Still, the guy in the link probably should have said microseconds. If you examine the video, it looks like the stuff flexes an inch or two before the bullet bounces off. Using 1000fps, 2 inches would represent about 160 microseconds.
Two inches could still hurt a lot, say on a bone, but it’s impossible to tell from the video how the back of the material is supported, and that’s important in getting more than a rough guess of the timeframe involved, as well as in evaluating whether the stuff would provide effective armor to a human.
If you want to play around with a viscoelastic material and don’t have a kilo of Silly Putty lying around, check in the kitchen for a box of cornstarch. As we learn from those two noted scientists, Penn & Teller, in their journal Penn and Teller’s How to Play With Your Food )1992), if you add a cup and a half of water to a box of cornstarch, the mixture is viscoelastic.
It appears to be a thick liquid, and you can easily move your fingers through it slowly. But if you smack or punch it suddenly, it becomes rigid. Hit it hard enough and you can even get it to form cracks. P&T suggest taking a glob and patting it into a ball, then tossing it to an unsuspecting friend. It’ll pass through his fingers.
A quote from the book explaining the science behind it: “The cornstarch forms really long-chain molecules. When the gunk is diluted or deformed gently and slowly, these honking chains can rearrange themselves and stay liquid. But, when there’s enough of these molecules crammed together and the impact is fast and hard enough, they don’t have the time or room to rearrange their big old selves. They stay all tangled, and the viscosity becomes enormous. With violence all around it, the slime cops to a solid.”
After buying the book I got some cornstarch and spent a couple of hours playing with the stuff. It’s very entertaining. (I stopped short of shooting it with a pistol.)
http://www.crayolastore.com/product_detail.asp?T1=CRA+08-0001-0-001&.
5 pounds for $80. I think I saw it cheaper in bigger quantities elsewhere before but I cannot find it now.
This is a video of throwing 50 pounds of silly putty off a building. Dow Corning 3179 Dilatant Compound is reported to be silly putty.
If I were a scientist, and I’d gone through 3178 compounds to invent silly putty… I think I’d have to kill myself.
Crazy Aaron’s Thinking Putty 5 pounds for $100-$140, depending on type.
If you go to their “tricks” page, they have several videos of people shooting huge wads of putty from a potato cannon. If you do a bullet-proofing experiment, be sure to send them a copy of the footage.
Christ. Google hounds: the net is a wonderful place, but it is full of incorrect information. Sometimes (gasp!) you need to know what you are doing. I know, I know, wouldn’t it be wonderful if google could make everyone an authority?!
I don’t care what wiki says. Viscoelastic is general term for materials with viscous and elastic properties. The stress/shear curve could be doing any number of things. Non-newtonian is also a generic term for a non-linear response to shear. Thixotropic is dead wrong. This is shear thinning.
Dilatant is shear thickening. Low and behold, if you use a non-google patent miner, you would find several patents and applications for armor using dilatant materials. It’s not a new idea, but I don’t think any practical applications exist yet.
I went to the Discovery Channel website and didn’t see a way to contact Adam & Jamie directly. However, I did post the following message on the Mythbusters message board.
Well, being as Q.E.D. has contributed to this thread, I think we have an inside track to the producers.
If I can add my own two cents to the idea, although the people who made the video that gazpacho linked to obviously went to some trouble, it leaves a lot to be desired: no close-ups, no ultra slo-mo. A few serious experiments by the Mythbusters with the stuff, dropping it from great heights, testing its properties, concluding with shooting at it with a gun, could make a couple of very good (and not too expensive) segments for the show.
Whaddya say, Q? Will you pass it along for us?
No, silly putty cannot stop a bullet. The problem with the silly putty armor approach is that after a certain point, the projectile is going to interact with the dilatant material as if it were a brittle solid. The shear rate will exceed the rate at which the polymer chains can slide paste one another, and the material cracks or shatters. The material isn’t even necessarily that tough at these high shears.
The patents typically involve a composite approach. Picture a pillowcase made out of Kevlar, with the pillow made of silly putty. Now you have the beginnings of a solution. The putty will absorb some kinetic energy before brittle failure, and then you rely upon the kevlar penetration barrier. I still think this approach is limited.
Better would be a multilayer sandwich structure, with alternating layers of penetration barriers (Kelvar) and/or impact resistors (epoxy coated carbon fiber) and kinetic energy dissipators (in our example, silly putty).
Most practical would be composite honeycomb structures filled with silly putty, faced with Kevlar or carbon composite, and stacked in multiple plies. It would not be too great an engineering problem to squeegee silly putty into open cells before laminating on the cap face. I didn’t find a patent for this approach, but I wouldn’t be surprised to learn that there were applications under review.
My apologies, Master. We bow before your superior wisdom.
I think you should reserve the Master talk for Cecil, or your favorite dominatrix.
I don’t have an objection to google-assisted wags and the like as long as it’s clear that is what they are. The best forum for getting a factual response to a unique question doesn’t work so well otherwise.
It would become endochronic.
How so? Does he work for The Discovery Channel or something?
Q.E.D. was recently hired as a writer or researcher or something for the Mythbusters show. Way awesome.
I’d search for the thread where he announced it, but I gotta run.
You’re a little unclear: are you saying that dilatant is the correct term?
I, personally, was not going on a google search when I suggested that term. I was going on the fact that I have participated in an order of 100 lbs of “coral-colored dilatant compound 3179” from Dow Corning, which lends some (but not total) credence to the idea that “dilatant” is the proper term.
For what it’s worth, the Crazy Aaron’s Thinking Putty FAQ doesn’t mention compound 3179 but it does tell the familiar story of the origin of a “Bouncing Putty” at Dow Corning and says that this putty is the primary ingredient in Thinking Putty.
did I read something about using spiderwebs for this? or am I dreaming?
Yeah, you have it right.
Catching fighter jets on aircraft carriers?