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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.'"
http://www.rexresearch.com/rabiei/rabiei.htm
1960s and 1970s cars prove him wrong. Those vehicles had a high rate of impaling the driver on the steering column in a crash of high enough speed and the accident rates were no better.
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.
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.
Well, and elastic just describes it's tendency to return to it's original shape, it says nothing about how much energy it's going to take to make it change shape in the first place...We're talking about a block of aluminum filled with hollow steel balls here. Anything short of a sledgehammer isn't going to change it in the least.
ad logicam Claiming a proposition is false because it was presented as the conclusion of a fallacious argument.
We just griped about that.
>capable of compressing up to 80% of it's original size
"It's" == "It is." No exceptions.
The genitive of "it" it "its."
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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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Actually, they would take fewer risks.
Okay, let's play out a scenario here.
You are at a stop light in the middle lane, with a vehicle in front of you and vehicles on both sides of you. It is winter time, and the roads are slick. A vehicle coming up behind you skids on the ice and cannot stop in time. You are boxed in by all the other cars on the road and cannot go anywhere.
Kindly explain how you are going to "avoid" this collision.
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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Yes. There are ways to minimize the chance of getting rear-ended at a red light.
1. Pump your brakes when a car comes into view in your rear-view mirror. Your flashing brake lights increase the chance the other driver will recognize the situation and stop in time.
2. Stop at least a car length before the white line at a stop light. If a car looks like it is going to rear end you, you have at least one (if not two) car length space to move forward and to the side to avoid a collision.
3. Avoid driving at times when it is likely other drivers are not alert (late at night, and the post-dinner tipsy driver time).
4. Avoid driving when visibility is poor.
It boils down to: not putting yourself in bad situations; making sure you are alert and focused on sources of risk; doing your best to make sure other drivers are aware of your position, speed, and intentions; and having an escape plan if something bad happens.
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Kindly explain how you are going to "avoid" this collision.
Simple - In the George Carlin system, if you're smart you don't drive when there is a chance of ice on the road during the day.
This stuff is nice, but it's a mistake to look at it as a drastic improvement in terms of safety.
The benefit of this is the reduction in weight without loss of strength.
ad logicam Claiming a proposition is false because it was presented as the conclusion of a fallacious argument.
On a day where grammar and spelling made the front page, surely we can use the correct "its" ?
100MPH+ crashes are fairly common in Formula 1. The driver almost universally survives. In fact, the last Formula 1 fatality happened in 1994. This material might be too heavy to work for Formula 1, but if it can give other cars a bit of the same safety, I'm all for it. If the car magically springs back into shape after a crash, so much the better.
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When they develop an airbag that can detect your position and avoid punching you in the face, I'll want one. I had one in my Subaru and was always thinking about replacing the steering wheel and getting rid of it in the process. Neither of my vehicles have them and I like them that way.
If you really care about safety, the thing to do is to wear a helmet and a five- or six-point harness (males prefer six) when driving. The helmet is there not so much to protect your head as to give you a place to mount a head strap.
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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.
For a steering column, you want a structure with very high torsional stiffness, but very low longitudinal stiffness. You don't want it to deform at all when you turn it, but if it's compressed along its length, it should do so readily.
I believe today's steering columns already do this to some degree.
Vehicular armor is a much more likely use with the foams we have today.
Not likely. Most anything that penetrates vehicle armor today is gong to cut through that stuff like like air. Things that take out vehicle armor include high velocity penetrator rounds and shape charges. Shape charges work by super heating copper alloy and pushing through armor. Its literally hot butter through a knife. Penetrator rounds work by going a couple thousand feet per second, combined with a small frontal area of a super hardened projectile. There is no indication this material will have any affect in this area.
On the other hand, unlike what you see in the movies, being shot while wearing a bullet proof vest typically results in black and purple bruises at best and more typically broken bones. Basically these vests prevent penetration. But even though it stops penetration, the blunt force trauma is still transfered! Think of a heavy aluminum baseball bat hitting, full swing, for every bullet stopped. And THAT force can very likely be significantly reduced using this material.
As for military applications, ceramic plates are typically used but those plates don't cover your entire body; else it would seriously inhibit mobility. That's why so many want to see Dragon Skin issued to soldiers. Which is to say, it completely stops the transfer of energy in addition to the projectile. Additionally, Dragon Skin is more effective as stopping nade shrapnel than is traditional ballistic armors.
Just the same, a lot of force is still transferred though both the anti-ballistic materials and traditional ceramic plates. Again, this may serve as a complimentary technology.
Also a bullet has anywhere from 8-18 inches to accelerate, a vest has to stop it in usually less than 2.
Which is irrelevant. Total momentum transfer is what knocks you over (or not), not peak force--it's the integral under the curve, not the peak of the curve that matters.
A bullet has a mass of 10 g or so--up to 30 for really big guns. It travels at around 500 m/s. That's 0.01*500 = 5 kg*m/s momentum, enough to impart a velocity of 0.1 m/s to a 50 kg (very light) person or 0.05 m/s to a 100 kg person (quite heavy).
Walking speed is a few m/s, so I don't see anyone being thrown back. Maybe staggered a little if hit by a really big gun. People are thrown back in the movies because people who don't know any physics think it looks good, but to those of us who do it makes as much sense as people being thrown up in the air by the impact of a bullet.
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It's not just about absorption of energy - a solid, stiff bumper can absorb energy. It's about rate of deceleration. The the theoretical minimum is total change in speed over total change in distance (constant deceleration). The minimum change in speed is fixed by the impacting speed and end speed. The maximum change in distance is fixed by the depth of the bumper. The way to minimize deceleration is to get the declereation to happen over a greater distance than the bumper: allow the engine compartment to crumple and cushion the deceleration, not just the bumper.
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.
Correct. For an example, take a large steel ball bearing and a solid rubber ball the same size. Drop them on a concrete floor from the same height.. The steel ball, being more elastic than the rubber(!) will bounce higher.
The ability of a metal to deform under compressive stress is malleability (the counterpart of this is ductility, which is a measure of tensile stress). Elasticity is an entirely different 'ticity.
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