Metal foam obliterates bullets • Hacker News Board

Re: Metal foam obliterates bullets

#11

Post by patio11 » Sun, Apr 10, 2016, 4:08 AM UTC

ZanyProgrammer wrote: post #6

Are there any potential downsides to this stuff? It seems too good to be true.

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."

Re: Metal foam obliterates bullets

#12

Post by Wingman4l7 » Sun, Apr 10, 2016, 4:18 AM UTC

hyperion2010 wrote: post #9

ceejayoz wrote: post #5

> 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.

Here's the doi for that paper: doi:10.1016/j.radphyschem.2015.07.003 Unfortunately I could only find the paywalled version here: http://www.sciencedirect.com/science/article/pii/S0969806X15...

The subreddit /r/scholar or the Twitter hashtag #icanhazPDF can help out.

Re: Metal foam obliterates bullets

#13

Post by patio11 » Sun, Apr 10, 2016, 4:19 AM UTC

colordrops wrote: post #7

Would this be effective against micrometeoroids and orbital debris?

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.

Re: Metal foam obliterates bullets

#14

Post by blisterpeanuts » Sun, Apr 10, 2016, 4:22 AM UTC

kibwen wrote: post #3

Neat, though of course this raises the question: what would it take to engineer a foam-piercing bullet?

Two projectiles. First one explodes on impact and compromises the target. Second one penetrates the target.

Re: Metal foam obliterates bullets

#15

Post by viraptor » Sun, Apr 10, 2016, 4:23 AM UTC

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.

Re: Metal foam obliterates bullets

#16

Post by rdtsc » Sun, Apr 10, 2016, 4:23 AM UTC

lolc wrote: post #10

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.

Re: Metal foam obliterates bullets

#17

Post by fiatmoney » Sun, Apr 10, 2016, 4:24 AM UTC

viraptor wrote: post #15

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.

In practice, you'd probably wrap the plate in fabric that would tend to catch the fragments, if nothing else because you need a plate carrier.

Re: Metal foam obliterates bullets

#18

Post by PhantomGremlin » Sun, Apr 10, 2016, 4:27 AM UTC

patio11 wrote: post #11

ZanyProgrammer wrote: post #6

Are there any potential downsides to this stuff? It seems too good to be true.

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.…

What about vehicle armor?

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.

Re: Metal foam obliterates bullets

#19

Post by SEJeff » Sun, Apr 10, 2016, 4:33 AM UTC

blisterpeanuts wrote: post #14

kibwen wrote: post #3

Neat, though of course this raises the question: what would it take to engineer a foam-piercing bullet?

Two projectiles. First one explodes on impact and compromises the target. Second one penetrates the target.

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:

http://www.digitalprognosis.com/album/images/iraqpics/the-st...

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.

Re: Metal foam obliterates bullets

#20

Post by refurb » Sun, Apr 10, 2016, 4:36 AM UTC

SEJeff wrote: post #19

blisterpeanuts wrote: post #14

Earlier quoted context omitted.

Two projectiles. First one explodes on impact and compromises the target. Second one penetrates the target.

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: http://www.digitalprognosis.com/album/images/iraqpics/the-st... The slats are smaller than the height of the outer explosive and prematurely detonate it. As a result, the penetrator simply bounces off th…

I thought the slats were to provide stand off distance for explosively formed projectiles.

If the explosively formed jet forms more than a few inches from the armor, it's way less effective.