Metal foam stops .50 caliber rounds as well as steel – at less than half the weight

Metal foam stops .50 caliber rounds as well as steel – at less than half the weight

Researchers have demonstrated that vehicle armor using composite metal foam (CMF) can stop ball and armor-piercing .50 caliber rounds as well as conventional steel armor, even though it weighs less than half as much. The finding means that vehicle designers will be able to develop lighter military vehicles without sacrificing safety, or can improve protection without making vehicles heavier.

CMF is a foam that consists of hollow, metallic spheres—made of materials such as or titanium—embedded in a metallic matrix made of steel, titanium, aluminum or other metallic alloys. In this study, the researchers used steel-steel CMF, meaning that both the spheres and the matrix were made of steel.

For the study, researchers manufactured a hard system consisting of a ceramic faceplate, a CMF core and a thin back plate made of aluminum. The armor was tested using .50 caliber ball and armor-piercing rounds. The armor was tested with the rounds being fired at impact velocities from 500 meters per second up to 885 meters per second.

The CMF layer of the armor was able to absorb 72-75% of the kinetic energy of the ball rounds, and 68-78% of the kinetic energy of the armor-piercing rounds.

"The CMF armor was less than half the weight of the rolled homogeneous steel armor needed to achieve the same level of protection," says Afsaneh Rabiei, corresponding author of a paper on the work and a professor of mechanical and aerospace engineering at North Carolina State University. Rabiei, the inventor of CMF, has spent years developing and testing CMF materials.

Credit: North Carolina State University

"In other words, we were able to achieve significant weight savings—which benefits vehicle performance and —without sacrificing protection," Rabiei says.

"This work shows that CMF can offer a significant advantage for vehicle armor, but there is still room for improvement," Rabiei says. "These findings stem from testing armors we made by simply combining steel-steel CMF with off-the-shelf ceramic face plates, aluminum back plate and adhesive material. We only optimized our CMF material and replaced the steel plate in standard with steel-steel CMF armor. There is additional work we could do to make it even better. For example, we would like to optimize the adhesion and thickness of the ceramic, CMF and aluminum layers, which may lead to even lower total weight and improved efficiency of the final armor."

In previous work, Rabiei and her collaborators demonstrated that CMF could block blast pressure and fragmentation at 5,000 feet per second from high explosive incendiary rounds detonating only 18 inches away. Her team also showed that CMF could stop a 7.62 x 63 millimeter M2 armor piercing projectile at a total thickness of less than an inch, while the indentation on the back was less than 8 millimeters. For context, the National Institute of Justice standard allows up to 44 millimeters indentation in the back of armor.

In addition, Rabiei's group has shown that CMFs, in addition to being lightweight, are very effective at shielding X-rays, and neutron radiation—and can handle fire and heat twice as well as the plain metals they are made of.

"In short, CMFs hold promise for a variety of applications: from to shipping , explosives and hazardous materials, to military and security applications and even cars, buses and trains," Rabiei says.

The new paper, "Ballistic Performance of Composite Metal Foam against Large Caliber Threats," is published in the journal Composite Structures.

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More information: Jacob Marx et al. Ballistic Performance of Composite Metal Foam against Large Caliber Threats, Composite Structures (2019). DOI: 10.1016/j.compstruct.2019.111032
Citation: Metal foam stops .50 caliber rounds as well as steel – at less than half the weight (2019, June 5) retrieved 17 June 2019 from
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User comments

Jun 05, 2019
In the video, there are lots of fragments released on impact. For space-based applications, you would not want pieces like that coming off and potentially becoming a factor for other ships in orbit or following you.

Jun 05, 2019
7.62 x 63 millimeter M2 armor piercing projectile: more properly known as the 30-06.

Jun 05, 2019
"more properly known as"

until you are crouched in a slit-trench, in the middle of a unbearably noisy battlefield.

screaming into a field-phone, your need for the ammo,
the specific ammo your weapons need.

to someone who absolutely needs to understand what you are requesting.
without having to guess.

be nighty, uhhmm, embarrassing?
if you are delivered a few cases of cookware instead of rounds for your rifles?
as in em-bare-ass-hanging-out-to-dry?

Jun 05, 2019
i am considering that the research in this article might usefully be combined with the work described in the kink below.

It is a barely acknowledged handicap for manned space flight.
The lack of reliable shielding from material debris & spectrum of radiation.

Right bow, the best we can do is gold foil. Generally adequate against radiation but suffers from being fragile to any physical abuse.

The methods being researched in this article, combined with the "noble" foams described in the other article?

Would help resolve several problems faced by long-termed manned spacecraft & habitats
Maybe reducing material supply costs as well as the expense in delta-v?

Utilizing gold-foam instead of foil?? Would make it a lot easier to handle in any environment.
& simplify repairs for micro-rock damage?

i am confident there would be mire possible procedures that could prove useful.

Jun 05, 2019
In the video, there are lots of fragments released on impact. For space-based applications, you would not want pieces like that coming off and potentially becoming a factor for other ships in orbit or following you.
So what do you think the alternative is?

"Most "space junk" is moving very fast. It can reach speeds of 4.3 to 5 miles per second. Five miles per second is 18,000 miles per hour. That speed is almost seven times faster than a bullet. And if a spacecraft is moving toward the debris, the total speed at which they collide can be even faster. The average impact speed of a piece of orbital debris running into another object is 22,370 miles per hour."

-If it hits, its going to shatter.

Jun 05, 2019
or liquefy.

Jun 05, 2019
or liquefy.
No sign of that here, and that's not surprising; liquefaction requires more time than is available here.

Jun 06, 2019
1/2 the weight for the same armor piercing capability is pretty good. Not sure that's exactly what we're looking at because. . .

With regular solid metal armor, up until you actually shoot something at it powerful enough go right through, there is both minimal back wall indentation AND very, very minimal cratering on the front wall, if any. Here on the video you can see significant crating on the front wall even with rounds that bounce off. Problem with that is what happens to the structural performance after the first few shots? That type of armor degradation is acceptable for some applications like security patrols, civilian armored cars, etc. However, armor degradation like that is not acceptable for a tank or a troop transport.

Given a few minutes and effects on target, a light machine gun would eat through a tank protected by this stuff when normal solid tank armor would repel such fires all day long.

Jun 06, 2019
Here on the video you can see significant crating on the front wall
No you cant. You actually think you can judge the performance of a material from a video on the internet??

Jun 06, 2019
@Jax, that's actually, if you'll pardon the pun, a fairly penetrating evaluation.

So basically this stuff is better suited for civilian use (SWAT teams and so forth) than military.

But I wonder if this wouldn't work in multi-layered armor as replaceable panels.

Jun 06, 2019

I served, I can tell from the video.

@Da Schneib

Yeah it could work as replaceable panels, but if you multi-layer it you don't gain any weight advantage and you get double the bulk.

Jun 06, 2019
Ha. You served. WTF good is that?? I've shot 1000s of rounds thru dozens of guns at many different materials. And I KNOW that the only way to judge performance, is to do a controlled study like the above, not watch a FUCKING video.

Your shit dont flush here.

Jun 06, 2019
Go check out an M1 Abrams armor that has seen small arms fire.

I shoot at steel plates every few week at the range. I know what cratering looks like, and I suspect you do too, if what you say is true. I also know my solid steel plates don't show cratering even after hundreds of rounds whenever they are thick enough, depending on the caliber, only some surface spatter scoring from spalling ammunition. If what you say is true you are a liar.

Hint: look at the the giant craters in the middle of the giant cracks that split the whole plate in the video. Lol.

Jun 06, 2019
Check out a few Utube videos of rifles target shooting at steel targets. Lol.

Jun 06, 2019
Now check out a few Utube videos of armor piercing rounds going through steel plates that are too thin. Notice the clean through and through without the giant spiderweb of cracks you see in the video with this stuff. Lol.

Jun 06, 2019
so, johnson929 & cyberhackspy01 @ gmail com
are quisling subversives for the Axis Dark Web?

No wonder sillyegghead, benni, & all the rest of the woomongering looneyticks
are ashamed of their employment.
Upchucking fascism & stuporstition all over the internet.

Jun 07, 2019
I would be much more interested in the radiation shielding tests.

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