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Exactly what it says on the tin: how thick would a layer of spider silk need to be to stop each of the following bullets from passing through?

I mean "on a separate basis", by the way; obviously, the thickness required to stop a .22 Short round is going to be a lot less than that for a .30-06 Springfield. Obviously, the thickness required to stop a .30-06 Springfield round would stop the .22 Short ceteris paribus; I'd just like to know what the minimum is to stop each of the above.

Assume the following material properties for this spider silk:

  • 1300 megapascals tensile strength

  • 1.3 grams per cubic centimeter density

  • 120 megajoules per cubic meter energy density

  • Capable of stretching 5 times its relaxed length without breaking

  • 111 megajoules per cubic meter toughness

Also, assume that it's a single layer of spider silk, rather than a bunch of spaced sheets, and that the bullets are normal ones for their caliber, rather than armor-piercing, high load, etc.

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    $\begingroup$ @ARogueAnt. en.wikipedia.org/wiki/Energy_density and en.wikipedia.org/wiki/Toughness $\endgroup$
    – KEY_ABRADE
    Oct 27, 2021 at 11:19
  • $\begingroup$ Wow, I learned something from that, thanks. $\endgroup$
    – Escaped dental patient.
    Oct 27, 2021 at 11:23
  • $\begingroup$ You don't want a single layer, you want multiple layers that slowly bleed off the bullet's energy. Same principle as light, really: A thick sheet of crystal allows virtually all light through, but a thin sheet of paper is opaque, as the paper has multiple grain boundaries and energy is dispersed at each boundary, while the crystal has only the two boundaries at its extremities. $\endgroup$
    – nzaman
    Oct 27, 2021 at 12:13
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    $\begingroup$ As a rough guide, NONE of those will be stopped by spider silk. The silk is too flexible, and will simply fold around the projectile, entering the body with the bullet. By the same logic, all of them will stop the bullet from passing through. But will perform no armor action in the process. You need to specify the backing, the tension of the silk, and whether is it acceptable (and to what extent) for the silk to accompany the bullet into your body despite not being penetrated. A description of what is meant by "a solid layer" of silk would be handy, too, because that does not exist $\endgroup$
    – PcMan
    Oct 27, 2021 at 15:47
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    $\begingroup$ "it can be woven tighter to prevent it from entering the body with the bullet" <- not as much as you might think. Spider silk is much more stretchy than Kevlar. Part of its "superior strength" comes from its ability to deform instead of break. Weaving it tight enough to make it more or less solid means it is already under a lot of tension putting it closer to it's breaking point. Instead spidersilk should be laminated with other materials or treated with sheer activated polymers if you want it to stop a bullet. On it's own, it is not a great material for body armor. $\endgroup$
    – Nosajimiki
    Oct 27, 2021 at 16:59

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Considering the fact that bulletproof Vest does not "stop" bullets - technically it slows them down at a very short distance - you may assume some faulty premises.

First of all, it's not new idea - there were successful attempts at building what you're asking about. The problem is that, as mentioned above, the way vests work will not help you with your problem.

Mainly because of the secondary effects of projectile hitting target (in this case human body), like hydrostatic shock. I will simplify the issue here, so please be kind.

Bullet enters body and depending on speed and caliber it does a lot of damage by "compressing" the impact area first, for fraction of a second, causing a shockwave expanding from the point of impact. In fact, this hydrostatic shock is the main killer, especially in the area of vital organs.

That is why vests are composed of multiple layers - to have that small distance to slow the projectile in order to BOTH prevent penetration of the skin AND dissipate enough of energy by spreading it onto larger area.

Even if vest "stops" the bullet it will still hurt. To describe it more graphically - instead of a very sharp, small bullet you're hit with huge sledgehammer.

So no matter how tightly woven will be the material of the single-layer, it may actually stop the bullet, but the shock will still kill the target.

There was a book I read some time ago where author introduced vest made of tubes of kevlar (of few milimeters of diameter), which gave the vest greater chance of stopping the projectile and at the same time greatly expanded the are onto which the kinetic energy is transferred, in effect making bullet stops merely uncomfortable kicks. Maybe do it that way?

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