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Super Strong Metal Foam Discovered
MikeChino writes to tell us that a North Carolina State University researcher has discovered what appears to be the strongest metal foam yet, capable of compressing up to 80% of its original size under load and still retain the original shape. The hope is that this amazing material could be used in cars, body armor, or even buildings to absorb the shock from earthquakes. "Metal foam is exactly what you might think – a cellular structure made from metal with tiny pockets of space inside. What makes Rabiei’s metal foam better than others is that she’s been able to make the tiny pockets of space more uniform. And that apparently is what gives it the strength as well as elasticity it needs in order to compress as much as it does without deformation. Many tests are being performed in the laboratory to determine its strength, but so far Rabiei says that the spongy material has 'a much higher strength-to-density ratio than any metal foam that has ever been reported.' Calculations also predict that in car accidents, when two pieces of her composite metal foam are inserted 'behind the bumper of a car traveling at 28 mph, the impact would feel the same to passengers as an impact traveling at only 5 mph.'"
Some hot metal, a tiny straw, and a guy who's really good at measuring his breaths.
Needless to say, scaling is a problem.
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"...behind the bumper of a car traveling at 28 mph, the impact would feel the same to passengers as an impact traveling at only 5 mph,,,"
George Carlin used to point out that if you put a large spike on the steering wheel so that the driver would suffer badly in a collision, the numbers of collisions would drop dramatically.
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Uniformity is one of the hardest things to accomplish when manufacturing anything. If it were easy, then first pass yield would be 100% every time. In reality, you are lucky if FPY reaches 95%, and if you've ever been in quality control, you know that 95% FPY is shit depending on the industry. If you aren't above 99% your nothing.
This is especially important and difficult in metallurgy. This is why there are highly trained material scientists and metallurgists working in the Aerospace industries. A well designed part is worthless if the heat from the tools changes the metal properties at the joints.
To go back to TFA, how would you suppose you form a foam out of metal? Now how you you ensure consistency?
I don't know, and neither do you. That's why it's a breakthrough.
http://www.rexresearch.com/rabiei/rabiei.htm
Place this behind an existing body armor compound (one that stops the bullet) and use the foam to absorb the remaining shock. Then you could survive being shot and also continue to return fire without being thrown back or suffering bad bruising.
Maybe, maybe not. Elasticity is not the same thing as softness... steel is pretty elastic, but you don't necessarily want a face full of it in a car wreck. OTOH, landing in a bed of inelastic potato chips wouldn't be particularly painful (though it would be itchy).
The foam is made by filling a mold with hollow steel spheres and then filling the gaps with molten aluminum. VERY scalable.
I wonder how it would fair if, instead of using molten aluminum to fill the gaps, you coated the steel spheres with aluminum (or other binder that melts at a temp lower than the spheres would start to collapse at) and sintering it into a solid block. More air gaps means it's lighter, but still very uniform.
=Smidge=
You'd rather have a big hunk of metal than an airbag? Don't let the "foam" fool you: slamming your face into a block of it at 35mph would only be a little better than running face first into a brick wall at the same speed.
It's squishy and springy...for metal. But it's not what you'd call soft.
ad logicam Claiming a proposition is false because it was presented as the conclusion of a fallacious argument.
Airbags and bumpers serve two entirely different purposes.
If this material lives up to the hype (unlikely), your next car will feature both items.
I'm curious to know more about the 28mph -> 5mph assertion. That stat was given to the media because it sounds impressive (grant guff), but how does it compare to the deceleration of a traditional auto bumper.
Two youtube videos about the material:
http://www.youtube.com/watch?v=mI5ZzfOlbKA - earlier video
http://www.youtube.com/watch?v=wfFcs25KmMc - one week old video
Shows among other things compression tests of the material.
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TFA is a poor re-blog of the original article here, which has this video, where you actually hear how it is made: Hollow steel balls are pored into a from, (and presumably agitated to settle them in a uniform matrix), then aluminum is pored over them to fix them there. So yes, should scale up well.
I hate seeing this comment on every science article mentioned. It reflects a common attitude among people and corporations, and it is, in many ways, the wrong attitude. Yes, many ideas aren't scalable. But there is, and needs to be a lag time between discovering something and then figuring out how to manufacture and apply it. If we only concern ourselves with something we can bring to market tomorrow then a lot of items will never see the light of day. Some science needs time to develop, and it isn't any less impressive if they haven't already started building the factories to put these in [insert application here].
The foam is made by filling a mold with hollow steel spheres and then filling the gaps with molten aluminum. VERY scalable.
Well, yeah, if you assume hollow steel spheres are "off the shelf". Kind of like saying starships are very scalable, you just make them with warp drives, problem solved.
I have cast aluminum and have had porosity problems. Basically some gasses dissolve better in hot aluminum and bubble out as it cools. Preventing porosity in castings is very old technology. I always assumed metal foams did the opposite of preventing porosity, and tried to supersaturate molten metal with hydrogen or argon or something under pressure and then froze it at a rate that grew the bubbles to just the right size. Metallurgists have no problem doing all kinds of complicated heat treatments and all kinds of weird alloys, so I figured the limitation was dissolving enough "whatever" in the metal to make it work.
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Au contraire! Some of the impact force will compress the foam, instead of compressing the child's head.
My testing has conclusive shown that a child's head, impacted at 25 mph by a block of this foam, will compress only 3 inches, compared to 5 inches when hit by a piece of solid aluminum.
Clearly this means that children will be 40% less dead when hit by a Canyonero driven by a soccer mom texting her neighbor's landscaper about getting her garden tilled*, provided that the Canyonero is equipped with this foam.
*And by getting her garden tilled, I mean having her bushes trimmed**
**And by having her bushes trimmed, I mean having bulbs planted***
****And by having bulbs planted, I mean having roots... oh screw it. I mean having a tryst.
"Trolls they were, but filled with the evil will of their master: a fell race..." -- J.R.R. Tolkien on Olog-hai
Damn, and we already shipped all of our tiny straw manufacturing over to China!
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I read it as his desire to use this foam as a replacement for the bumper and crumple zones. It would turn the existing crumple zones into something in the car's frame and bumper system that would absorb a great deal more of the impact and, therefore, largely eliminate the need for airbags.
I'm not sure I'm buying it, though. Airbags are an "also need" feature, and cannot be replaced wholly by a better crumple zone.
The problem lies in the elasticity and the distance. If you hit a brick wall doing 65MPH and your crumple zone is too squishy, it will continue crumpling up until you are included in the crumple zone. In other words, you're dead.
Make it too hard, and the car will stop more quickly than your flesh can handle. The airbag is a crude but effective way of allowing a relatively stiff crumple zone that can manage to keep your passenger cabin intact during a VERY major impact, and still accommodate your body's need to decelerate as gradually as possible. If you hit a brick wall doing 65MPH, the crumple zone decelerates the car from 65MPH - 0MPH in the distance represented by the zone (usually a few feet at best), and materials aren't going to improve on that a whole hell of a lot. You are still going from 65MPH-0MPH in just a few feet. That's a SERIOUS amount of deceleration.
The airbag is what takes your head and torso and slows them down as gently and slowly as possible, leveraging the deceleration already provided by the crumple zone and making the best use of it to keep your brains from splashing around in your noggin, and/or snapping your neck. Which is not to say the airbag is gentle or slow at all, far from it, just more gentle and slower than making your dainty neck bones absorb all of the force as your torso is stopped by the seatbelt and your several pounds of head really wants to keep going to make Newton happy.
Could be worse, though. You could be wearing no seatbelt at all and expect your chest and head to absorb all of the speed when they impact the steering wheel and windshield respectively. That always ends colorfully, particularly in shades of red and grey.
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You know what’s ignored and missing in this discussion?
The question of what the spheres are filled with!
Because they are certainly not “filled” with a vacuum.
But I think there got to be cool properties and applications, when you fill them with something else than air.
Any sufficiently advanced intelligence is indistinguishable from stupidity.
Do you have physics to back you up? No, I didn't think so.
Take a new Toyota Tacoma. Assume weight savings in replacing bumper with foam metal is used elsewhere so you have the same mass vehicle. A Tacoma weighs approximately 4000 pounds, which is approximately 1800 kg.
Kinetic energy is given by:
e=0.5*m*v^2
m = mass
v = velocity (or speed for our purposes).
The kinetic energy of a Tacoma moving at 28 miles per hour is approximately 141 kJ.
The kinetic energy of a Tacoma moving at 5 miles per hour is approximately 4.5 kJ.
That is, the foam bumper only has to absorb 31 times as much energy as the solid bumper to perform to the quoted standard.
See quote below, which is from here: http://www.rexresearch.com/rabiei/rabiei.htm
We see they estimate a factor of 80 improvement of energy absorption over the foam metal's equivalent bulk material. They don't say, but let's assume (reasonably) that they are talking about linear compression. Let's assume for a second that the stock bumper is made of a block of solid steel that doesn't absorb any energy. It's not, and it does, obviously.
If their estimate is correct, and a foam bumper of the same size will absorb 80 times as much energy as its solid counterpart, then the passenger in the 28 mph impact would feel 1-2 kJ of energy instead of ~140 kJ of energy. Obviously the bumpers are not solid metal, and they already have some energy absorption capabilities built into them.
Based on the factor of 31 between the kinetic energies of the vehicle at different speeds, I think their claim is the opposite of bullshit. It's reasonable.