Does anyone know how this works? I hypothesize that the reason that the bullet shatters is that boron carbide is much harder than the copper of the bullet. Does anyone think that this may be made into a conventional armor design as some people are saying or is boron carbide too expensive for use in this application? Link: http://www.slate.com/articles/video/video/2016/04/metal_foam_armor_can_shatter_bullet_on_contact_video.html

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    $\begingroup$ You are asking several questions here. It's considered good form not to do so. BTW, why do you think 'hardness" has anything to do with shattering the Cu? A bullet will shatter a glass plate, yet the glass is much harder than Cu. $\endgroup$ Aug 8, 2018 at 17:59
  • $\begingroup$ Doesn't the softer object generally shatter first in a collision between them by its Mohr hardness value? $\endgroup$ Aug 8, 2018 at 19:17
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    $\begingroup$ Syntactic foams have been under development for armor and blast mitigation since the mid fifties. The key is that the cenospheres largely govern the compressive properties of the foam and the matrix largely governs the tensile properties of the foam. This separation of bulk properties is really handy for blast and impact management. Strangely, a lot of the effect seems to have to do with managing the speed of sound in the material. When spheres collapse, you can get ridiculous little pressure jets of matrix material. I suspect that's what is blowing the bullets apart. $\endgroup$
    – Phil Sweet
    Nov 22, 2018 at 15:35

1 Answer 1


The bullets won't actually 'shatter' as they are soft lead (in a copper jacket). Bullets normally deform on impact with a hard surface (such as armour) and will spread out (like plasticine). Some of the energy normally goes into deforming the armour and denting it, but if the armour was hard enough and stiff enough, it could resisit the bullet enough making (almost) all of the energy from the bullet go into deforming the bullet itself. This looks to be whats happening in the video where the armour doesn't move or deform and the energy is focused into spreading the bullet out so much it breaks into small pieces.

The only problem with hard materials is that they are normally also brittle (as in ceramics). While the armour works great for smaller bullets something with enough energy could potentially cause the armour to shatter (although without having details of the armour it's impossible to tell).

If someone is developing it as an armour then it's safe to assume they will be looking to use/sell it and will likely have some plan to do so. But there may be more development required in order to reduce costs to the point someone will pay for it, or allow it to be manufactured more easily.


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