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Metal foam obliterates bullets

phys.org

21–30 of 89 posts

Re: Metal foam obliterates bullets

#21

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.

Yes, I understood that as "turns bullet into shrapnel" which sounds rather problematic.

Re: Metal foam obliterates bullets

#22
post #13

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.

Delta-v is defined as "change in velocity", ie. how much a spacecraft can change its velocity. I think you're talking about relative velocity.

Re: Metal foam obliterates bullets

#23

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.

The effect is called "spalling" and current steel and ceramic armor plates are coated in a layer of rubber material to catch the fragments.

Re: Metal foam obliterates bullets

#24

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.

Re: Metal foam obliterates bullets

#26
post #13

Earlier quoted context omitted.

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.

Delta-v is defined as "change in velocity", ie. how much a spacecraft can change its velocity. I think you're talking about relative velocity.

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.

Re: Metal foam obliterates bullets

#27
post #13

Earlier quoted context omitted.

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.

Delta-v is defined as "change in velocity", ie. how much a spacecraft can change its velocity. I think you're talking about relative velocity.

Yep; appears I misremembered a long-ago physics class.

Re: Metal foam obliterates bullets

#29
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.

Re: Metal foam obliterates bullets

#30

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.

Yes, I understood that as "turns bullet into shrapnel" which sounds rather problematic.

Sales opportunity.
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