This doesn't have much in the way of interesting details, you need to go to the paper for that.
The armour is a composite sandwich, with boron carbide on the front face (a hard ceramic), followed by the metal foam, and either aluminium or kevlar on the rear face.
The boron carbide layer blunts the bullet and distributes the compressive stress over a large area of the metal foam. The metal foam is made of 2mm-diameter hollow steel spheres in a stainless steel matrix (created using powder metallurgy). The metal foam deforms plastically under the compressive stress, absorbing the kinetic energy of the projectile (i.e. the spheres get crushed). The backplate provides tensile strength and stops the foam from tearing apart due to residual tensile stresses.
Dragon Skin (https://en.wikipedia.org/wiki/Dragon_Skin) claimed to withstand multiple hits without loss of performance, although there was some controversy around it.
Problem is, US Army procurement is sufficiently corrupt you can't trust testing of any physical item you hand to them, this goes back at least to the '50s when they caused the AR-10 to fail by replacing screws with wire springs....
That said, the design is obviously way too heavy without anyone even needing to weigh it.
"Once" though is one event, which might include your body armor getting hit more than once. If you're up against automatic weapons, especially the more stable heavy ones (e.g. belt fed General Purpose Machine Guns), a plate getting hit more than once in one moment is fairly likely. The military SAPI and ESAPI standards require stopping 3 hits: https://en.wikipedia.org/wiki/Small_Arms_Protective_Insert
Because I imagine I wasn't the only one with no clue what "spall" was:
> Spall are flakes of a material that are broken off a larger solid body and can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ball bearing)
It's unfortunate that the researchers couldn't find someone who speaks English fluently to write the paper with. Here's the abstract: "The application of advance [sic] materials to manufacture hard armor systems has led to high performance [sic] ballistic protection. Due to its [sic] light-weight [sic] and high impact energy absorption capabilities, composite metal foams have shown good potential for applications as ballistic armor. A high-performance light-weight composite armor system has been manufactured using boron carbide ceramics as the strike face, composite metal foam processed by powder metallurgy technique [sic] as a bullet kinetic energy absorber interlayer, and aluminum 7075 or Kevlar™ panels as backplates[,] with a total armor thickness less than
25 mm. The ballistic tolerance of this novel composite armor system has been evaluated against the
7.62 × 51 mm M80 and 7.62 × 63 mm M2 armor piercing projectiles according to U.S. National Institute
of Justice (NIJ) standard 0101.06. The results showed that composite metal foams absorbed approximately 60–70% of the total kinetic energy of the projectile effectively and stopped both types of projectiles with less depth of penetration and backplate deformation than that specified in the NIJ 0101.06 standard guidelines. Finite element analysis was performed using Abaqus/Explicit to study the failure mechanisms and energy absorption of the armor system. The results showed close agreement between experimental and analytical [sic] results."
I'm hoping they carried out their experiments (physical and simulation; in my book, FEA simulation results aren't "analytical") more carefully than they wrote the paper.
The foam does sound like a pretty interesting material! I've read about metal foams since my childhood, but the hollow-sphere-based foam seems significantly stronger than the more irregular foams.
* I guess you dislike the lack of hyphen in "high performance"? But then you dislike the hyphen in "light-weight"? But no comment about "high impact"?
* The "its" is actually "correct" (standard) usage.
* No article on "powder metallurgy technique"? Okay, sure, but this is an incredibly common mistake, especially for non-native English speakers.
* I would think simulation results are "analytical" by virtue of not being physical. Seems fine to me.
Most people are only native speakers of one language. The amount of effort required to iron out these extremely minor "problems" (if you accept your English teacher's notion that there really is a right or wrong way of using English) in a second language is simply not worth it for most people. They still got their message across, don't they? Their research is still understood and made use of, isn't it? So why not let it slide?
Yes, these things can grate on my nerves, too. But were I writing formal papers in languages that aren't native to me I would only hope to do as well as these authors appear to have done.
WRT "high performance", it's perfectly fine to write, "This armor has high performance." It's not actually incorrect, as far as I know, to write, "high performance ballistic protection", but it's unnecessarily ambiguous: the parsing that is intended is ((high performance) (ballistic protection)), but it parses equally well as (high (performance (ballistic protection))), which doesn't make sense, so we know it isn't the intended meaning. The authors use the less-ambiguous punctuation two sentences later. "Lightweight" achieved wordhood decades ago, maybe more than a century, and therefore has no need for the apologetic hyphen.
The issue with "its" is that it's singular, but its antecedent (or postcedent, if you will) is "composite foams", which is plural, and used with the plural form of "have". So "its" here violates pronoun-antecedent agreement.
The problem with violating grammatical rules (whether they're the rules of academic English or of AAVE) is not that it's morally wrong; it's that it makes you hard to understand. In fact there are people who would have understood and made use of their research who will not do so. If the errors were more serious, the number of people thus excluded would be larger, but it's still nonzero. Some of those people will simply remain ignorant of the results these researchers attempted to publish; others will get them from another source, perhaps an experiment done by someone who was ignorant of the results, assuming that the results are correct. Perhaps metal-foam composites research will lag behind where it would have been with a more coherent paper, and alternative forms of armor (aerogels, say) will become dominant instead, and the researchers and their research will languish in obscurity.
Another part of the problem is that the sloppy abstract signals to readers that the researchers had very low standards for the paper—perhaps if I attempt to reproduce their results, I will discover that they misstated the composition of their strike plate, omitted crucial details like the density of the spheres or which stainless steel they used for the matrix and how they sintered it, or even incorrectly measured the deformation of the backplate.
If you're writing formal papers in languages that aren't native to you, you should find a native speaker to write or at least proofread your abstract, if not the entire paper. Some people do this professionally at a cost substantially lower than the cost of fabricating a stainless-steel foam, so even if you're living in Bhutan, you can contract a professional writer. But the authors of this paper are at NCSU, which has 34000 students, over 29000 from the US, so presumably they have at least 25000 functionally-literate native English speakers in their very own university, most of whom would be willing to work for well below market rate and many of whom are actually interested in learning to Do Science.
But they didn't care about communicating their results.
I did modelling work for a group researching metal foams in my past academic life. Very interesting stuff with a lot of applications if the manufacturing processes can be nailed down.
Our funding was a mixture of European Space Agency and a car conglomerate: light armour for space vehicles and crumple zones / reinforcement respectively (less acceptable to research military applications in EU in my experience).
I asked Dr Rabiei that very question by email yesterday, and she is working on it:
"Let me start by saying that it is not a crazy idea and is actually what I have been working on recently. I even have a proposal in DARPA on testing the performance of the material at supersonic speeds. At this time, our data covers up to a speed close to 1Km/s as you mentioned. We have not tested the performance at higher speed and that is what I was hoping to conduct soon."
(I asked if it could be used for space debris at 8-15km/s, and apologized for asking a crazy question)
That would be outstanding if it could ... talk about the perfect material for shielding supercritical spacecraft components. Radiation resistance, projectile resistance, lighter than normal metal, temperature resistant... What's not to like?
I was thinking of a small amount to protect supercritical components; navigation computers, comms, life support (if applicable); not necessarily the entire spacecraft.
This presumably depends mostly on what your delta-V is. You can be wearing Epic Foam Platemail of the Whale +5 but if your orbital velocity is 7 km/s and you hit a 100g rock at the same velocity but going the other direction physics says you're about to have a very bad day.
I believe GP was referring to delta as in mathematics, which refers to difference and not necessarily change. So the delta between +7km/s and -7km/s is 14km/s.
You are technically correct, though based on common usage patio11 got their point across.
That would be a winning application. Something that I expect you could get NASA/SpaceX on board with, send some sheets up as ride along payloads for a resupply mission, put them in the bay behind the Dragon module on the second stage with some cameras, then use dragon as an uplink to look for space debris impact on the second stage as it re-enters and monitor the results. I would have to know more about what is available in the remains of the second stage to know how much mass you would end up adding for the experiment but I expect it would be less than a couple of kilograms.
The current designs already use dual hull - the first makes the projectile explode to dust, the second stops the debris. The critical problem is weight. That construction that is shown looks to be quite heavy relatively.
The part about shielding radiation sounds dubious to me. I thought shielding from radiation was mostly about mass. How is that foam supposed to shield better than cast metal of the same weight? Maybe the "foam" deteriorates less?
> I thought shielding from radiation was mostly about mass.
Not for all types of radiation. Neutron radiation for example is absorbed better by a hydrogen rich material like say polyethylene. But then during absorbtion it would emit gamma rays sometimes, so metal shielding is needed as well.
if you have something that interrupts the wave it blocks the whole wave. that's why the gauss on the microwave front door works yet you can see through it, because microwaves (the actual waves) are in the order of centimetres wide.
> Last year, with support from the Department of Energy's Office of Nuclear Energy, Rabiei showed that CMFs are very effective at shielding X-rays, gamma rays and neutron radiation.
Designers of spacecraft and lunar/Mars bases are likely pretty happy about this development.
This is exactly how a Soviet style RPG works. Ironically, it is also why the "bird cage armor" works so well against the RPG. Here is a picture of a Stryker combat vehicle from when I was in Mosul Iraq circa 2004ish:
The slats are smaller than the height of the outer explosive and prematurely detonate it. As a result, the penetrator simply bounces off the armor harmlessly.
Nope, we had them in Iraq before EFPs were really a thing (Thanks Iranain Quds Force for that). They were specifically for RPGs, which was one of the few things that could take out a Stryker without it. They even tried those Soviet parachute anti-tank grenades, but the Stryker is much faster than a tank and just moved away in time. That being said, the I'm sure this slat (birdcage as we called it) armor would help with that as well.
I thought an RPG _was_ an EFP? The round is just a shaped charge with a copper liner that penetrates the armour. So the slatted armour stops both RPGs and EFP-based IEDs.
The Vampir uses a tandem charge -- Two successive charges. The point of this is to counter reactive armor, which is designed to counter explosively formed projectiles.
No, you're right. Explosively formed projectiles work best when formed a few inches from the armor. However, they have a sweet spot and if the distance is too far, they don't work. I figured that's what the cages were for.
I though slat armour worked because RPGs only had a detonator in the nose, so unless you were very unlucky and the tip of the RPG hit a slat, the RPG would just jam itself between two of the slats.
I saw that a few times actually, but only when the idiot firing the thing didn't pull the safety pin out of the warhead. The RPG is surprisingly safe when you neglect to remove the safety and will happily fire, but not explode in that circumstance. It was around the height of the Fallujah offensive we saw that happen.
I've seen that before and I am so disappointed in the slow motion part. I wish I could see those bullets going one behind the other in a perfect 8 pattern.
I'm not an expert, but after some Googling, I think the bullet they're using there consists of a steel core inside a lead envelope inside a copper or copper-nickel jacket. So, at a guess, you'd want to replace the steel with something much harder and/or denser. Tungsten, maybe? I dunno. Depleted uranium would probably do it; I've never heard of it being used in anti-personnel rounds, but in cannon sizes it pokes holes in tanks quite nicely.
Indeed. The AP M2 round is the standard for National Institute of Justice (NIJ) Level IV rifle plate armor, but to the best I've been able to determine it's not a "serious" AP round, rather, it has a pill of relatively soft steel inside the normal lead and was developed in the run up to our involvement in WWII as much for the lower cost as the increased penetration. The latter of which was appreciated towards the end of WWII when I've read it became ubiquitous, and for example in city fighting one or more 20 round BAR magazines of this were used to knock holes in masonry walls between buildings.
It was probably made the NIJ standard because it's the only somewhat common AP ammo a US cop is likely to go against on the street, as noted by extrapickles the serious AP ammo is a lot more expensive, and I'll add not really legal any more since there are some pistols that'll fire it.
Notably, ESAPI military equivalent plates also aren't certified to stop anything more serious than AP M2, and I assume again for the same reason, there is or was a lot of surplus AP M2 ammo out there at one time. In the US civilian marketplace it's pretty much dried up as I understand it, e.g. see the few hits this GunBroker.com search finds and the prices: http://www.gunbroker.com/Ammunition/BI.aspx?Keywords=ap+m2 and I can't find any demilled bullets there or with a couple of minutes of Google time, whereas they were commonly available not too many years ago, certainly within the last decade.
There are several rounds the military uses for small arms. 50 BMG and 5.56 NATO both have tungsten versions, though they are expensive, and hard for non-military to buy (when found, $50/rnd). Even the military does not normally issue them due to the cost, which is ~2-10x of a standard lead+steel round.
I found the post-impact part of the video interesting. The article says "turn an armor-piercing bullet into dust on impact". But in the video, it looks like it turns it into a lot of metal particles / shrapnel. As a body armor it looks like it could be increase the danger to those around a person getting hit.
It's hard to say for sure since there's only five frames of video post-impact, but it looks like those fragments are slowing down really fast. In the first couple of frames they're moving faster than the bullet was, but in the last couple they barely move at all. It seems possible that they're only dangerous within a foot or two of the impact point, which seems like a very acceptable trade-off for the benefits.
Even if I'm wrong, unless it catches somebody in the eye, I don't think those little fragments could do worse than a flesh wound.
It's going to be expensive, may not meaningfully improve survival in actual combat situations, and may not actually be successfully deployed.
How could this be extraordinarily effective at stopping bullets but not meaningfully improve survival? Fairly few American soldiers are killed by gunfire which directly strikes them; even fewer of these soldiers are killed by gunfire which directly strikes them on their armor. (This is partly because armor is fairly effective, partly because bullets are often non-fatal, and partly because medical care is very good.) Improved body armor may not meaningfully improve survival against other threats such as, for example, IEDs (once 60%+ of fatalities, down these days) or "the helicopter impacted terrain at a high rate of speed."
If existing armor is already effective enough, improved materials means we can have the same effectiveness at lower weight. This could improve survival by increasing mobility or allowing soldiers to carry heavier non-armor equipment.
Something like this would be a great improvement over the very heavy homebrew plating that our guys in Iraq and Afghanistan were forced to improvise on their Humvees? I.e. before MRAP type vehicles made it into the field.
Lighter and better armor isn't just for people, it's also for vehicles.
It's actually very similar in a lot of ways to chobham armor, which is layers of ceramic and high strength metal in a composite structure. This seems to work similarly but with a more consistent mixture of both materials throughout a material, which might make it easier to manufacture and to work with, and possibly lighter as well.
This reminds me of an old Mythbusters experiment where they showed that covering a wall in the same stuff people put in the bottom of their trucks can protect the wall from explosions.
Looking at the ammo channel for I think the same ammo the results don't seem that remarkable. The foam article quotes "less than an inch", the ammo test article has about 1 inch for mild steel and 0.319 inches for AR500 plate
To hit someone in the eye, you've got to aim at their eye and land a round there. That is, accuracy at hitting a pre-specified target.
To hit armour in the same location twice, you need either two (or more rounds) delivered consistently on whatever happens to be where the first round lands. It's a case where being a Texas Sharpshooter actually works (painting bullseyes around the bullet holes you just shot into a barn).
A compound impactor with a leading and secondary round might work, for example. Difficult to package into a small-arms round, but possible. Keeping everything on the same impact point would be the crucial element.
At that point, wouldn't it be easier and just as effective to use a single, larger round? .50-cal rifles already exist; no need to invent a big bullet that turns into two smaller bullets.
(Unless you mean something that starts out the same size as the one in the video, in which case I can't imagine that two halves of a .30-06 would penetrate any better than one whole .30-06.)
There's often an advantage do a dual-mode strike. That's how many existing armour-piercing weapons operate. E.g., tungsten-alloy armor piercing rounds:
For anti-tank munitions two rounds work much better than a single larger round - the reactive armor is able to defend even against the larger round, but once it is hit once, it is gone from that spot until maintenance. E.g. the recent Ukraine conflict experience shows that many types of weapons can achieve successful penetration when (and only when) hitting essentially the same spot a second time.
And of course there are things like RPG-30 Kryuk to exploit that - fires two rounds, the first, triggering round is small and just enough to trigger the protective armor, and they're both fired at once from the same device to ensure that they hit the same spot just one of them tuned to hit juuuust a bit before the main round.
I read about it as a child. On earth, molten metals readily lose gas by the force of gravity, but in space, you can easily make metal foams that will be very strong and light. Sounds like a good material for spacecrafts.
Also, how about glass foam? I imagine you can blow large and cheap hulls from foamed molten glass.
The armour is a composite sandwich, with boron carbide on the front face (a hard ceramic), followed by the metal foam, and either aluminium or kevlar on the rear face.
The boron carbide layer blunts the bullet and distributes the compressive stress over a large area of the metal foam. The metal foam is made of 2mm-diameter hollow steel spheres in a stainless steel matrix (created using powder metallurgy). The metal foam deforms plastically under the compressive stress, absorbing the kinetic energy of the projectile (i.e. the spheres get crushed). The backplate provides tensile strength and stops the foam from tearing apart due to residual tensile stresses.