[dkbrk]

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.

[chillydawg]

Presumably very expensive and one-time usable. I guess that's true of most types of armour anyway.

[rmelly]

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.

https://www.youtube.com/watch?v=aYaSRIbPWkM&nohtml5=False

[mlhaufe]

Given that it weighed ~50 pounds and failed in a variety of environmental conditions, it's no surprise it wasn't adopted.

[1] <https://www.quora.com/Why-was-Dragon-Skin-armor-rejected-by-...

[hga]

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.

[coldtea]

>and one-time usable

It's not like you want it to save your life more than once...

[hga]

"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

[the8472]

There's a 4th layer: The whole thing is vacuum-wrapped in epoxy-fiberglass composite to catch spall.

[rattray]

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)

https://en.wikipedia.org/wiki/Spall

[nkozyra]

Odd that the video doesn't seem to catch spall then.

[tyingq]

Catching spall on the back side of the barrier is the important bit.

[cellularmitosis]

Why? Does the spall have enough energy to hurt someone?

[iSnow]

jagged splinters with sharp edges being ejected at high velocity - what could go wrong?

[kragen]

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.

[pc2g4d]

I will now nitpick your nitpicks ;-)

* I'll give you "advance".

* 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.

[kragen]

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.