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Idea: Kevlar gunshot injuries solution

  1. Jun 2, 2014 #1
    Hey guys,

    When you are shot with a gun you get hurt even if you're wearing kevlar. In some cases you even break ribs or puncture a lung.

    Are there no solid substances out there that hardens proportionally with the kinetic energy that is applied?

    If that was woven into the vest it wouldn't impair movement since the kinetic energy applied to the fabric is relatively low with regular movement, but a bullet would make it harden and prevent the full force of the impact from affecting a small area on the body.

    Wouldn't this be possible?
  2. jcsd
  3. Jun 2, 2014 #2


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    Hardness is a complicated property that is dependent on many factors, such as elasticity, plasticity, brittleness, and toughness. See a more in depth article here: http://en.wikipedia.org/wiki/Hardness

    To add to that, stopping a bullet takes more than just hardness, and body armor must be carefully designed so that the force and energy of the impact is spread out over a large enough area to avoid causing the armor to shatter/fail or the wearer from taking severe injury. Some very hard materials are simply too brittle and would shatter instead of deforming, which would only pose more of a hazard to the wearer. In addition, the weight and bulk of the armor is a very high point of consideration. Metal plates several inches thick would provide ample protection from small arms and rifle fire, but would be far too heavy and bulky to wear.

    Needless to say, research in improving body armor is ongoing.
  4. Jun 3, 2014 #3


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    1. There are attempts at using shear thickening materials (non-Newtonian fluids) as a body armor.

    2. No matter how hard the body armor is, conservation of kinetic energy and momentum of the projectile/bullet means you will be - at best - heavily shaken. That always hurts.
  5. Jun 3, 2014 #4


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    Welcome to PF AtotehZ

    As stated by Drakkith and Borek's posts, you are looking for Non-Newtonian fluids and there are attempts to make armor with these just that most cannot withstand the Energies of the smallest handgun bullets in a wearable form and size.

    Gelatin is "close" to a Non-Newtonian and you could search the abuse a 5lbs Gummy-bear gets on Youtube (I think it's posted by Taofledermaus). But for a full torso armor it would weight too much.

    Hadfield Steel hardens under stress, although there is no definite proportionality to it and it does not make it bulletproof in thin-sheet form. British Brodie Helmets were made of it and were good enough for shrapnel shells. Of course it is not flexible as this property is probably what you are looking for.

    Vests are backed against deformation with rubber, plastic composites, titanium or ceramics and depending on how they are build they can be flexible. See Dragon armor and Scale armor. As far as I know only the vests which offer low-grade protection against handgun rounds are left without backing.
  6. Jun 3, 2014 #5

    Those were the vests I had in mind. Some investigators wear these very thin vests. My point was exactly as Drakkith mentions, to make the energy dissipate over a larger area because of the hardening property, but preserve maximum movement and thinness. What I had in mind was backing of thin kevlar with something like a non-newtonian substance.
  7. Jun 4, 2014 #6


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    Non-Newtoinian fluids are as they are called fluids, the main characteristic of these is low to insignificant mechanical properties. You will need a thick amount to get an effect.

    It is easier to just distance the non-backed vest form the body by soft spacers (PU rubberized foam), or why not with inflated bicycle tire tubes. Thus the Kevlar absorbs more of the energy before reaching the body by forcing the bullet to pull a lot of fabric with it until it touches the body. Like the Japanese Horo (arrow catcher).
  8. Jun 4, 2014 #7
    Stretch Armstrong in your pocket

    When I was a young Marine, we played around with shooting at body armor with different objects behind the vest. We were always surprised at what worked and didn't work. Like using a fire ax to get through bullet-proof glass...worked the best.

    With body armor, there was a difference, of course, between flak jackets and actual bullet-proof vests. Metal plates in front of the vests worked best, but the weight and lack of flexibility were unpleasant. Different types of rubber, gel soles, etc... were played with. As I recall, we had a lot of success with several different types of Stretch Armstrong toys.

    If you recall, you could slowly squish and stretch a Stretch Armstrong doll if you did so slowly. If you tried to do so rapidly or quickly, the material acted very rigid and hard. Maybe we could get Mattel to make a Stretch Armstrong body armor vest liner? Or give a bunch of Stretch Armstrong dolls to the troops to carry in their pockets. Might relieve a lot of the boredom also.
  9. Jun 4, 2014 #8
    Distance the non-backed vest from the body

    NOTE: In the early days when the military did not supply bullet-proof jackets, some of the guys purchased their own, and would wear this over the flak jacket. Several guys got shot and had real good results. This would confirm your thought about distance the non-backed vest from the body.
  10. Jun 7, 2014 #9
    Just a guess here, wouldn't u make the armor break in only the parts you want to fail; like if you could weave thin, semi-brittle steal or aluminum cable that is meant to shatter, into the Kevlar. or maybe thin ceramic tiles.
  11. Jun 7, 2014 #10


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    I remember the USMC M1955 vests the marines had on the ship in the 70's, we had a few for the ships security alert force.

    I think the fluid is called STF but you still need some sort of trauma plate to spread the force from a bullet.
    http://www.ccm.udel.edu/STF/media.html [Broken]
    Last edited by a moderator: May 6, 2017
  12. Jun 7, 2014 #11


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    I see the problem as being the spreading of bullet energy. The energy of impact radiates in a widening cone from the point of impact, which would suggest you must intercept the bullet as far from the body as possible to spread that energy over as wide an area as possible.

    A Kevlar vest concentrates the remaining bullet energy by wrapping the bullet in a tight Kevlar conical well. That energy needs time to fall through tension in the Kevlar before remnant point energy reaches the body.
  13. Jul 22, 2014 #12
    Look at the law of impulse

    Someone in the above replies talked about distance between the body and the outsite of the Kevlar vest. Remember there is the so called impulse, defined as the product of velocity and mass of the bullet, which is equal to the produced force by time during bullet impact. Studying this equation, you will see, the shorter the impact time the larger the impact force to the body of the person is. This means, if there is zero way to decelerate the bullet speed, the force to the person would get infinit high. This gives the answer to your idea of having a hard vest: it will shock the person the more the harder the protection vest is. To reduce this shock impact to the person, you need to have a minimum decelerating way for the bullet. By the way, the working force at impact can be calculated by measuring the duration of impact, when you know the bullet weight and speed.
  14. Jul 23, 2014 #13


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    A link from a few years ago.

    That one's liquid, not solid. Not sure how much this really matters, seems like IED's were always more on your mind when I was in. AK rounds made plates even iffy as far as survival went, but I do remember one guy getting shot in the back. Broke his back but he didn't die.
  15. Jul 24, 2014 #14


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    Nice link and great concept, yet after 2 years I did not hear of a positive result.

    The main problem is with the so called "locking" of the ST-fluids particles, it will never compare in strength to bonding, as for a liquid to be liquid you need low molecular mass or low inter-molecular attraction. Even if you interlock the particles they will be either too small to add up or too "slippery" and in both cases their yield strength will not amount to much.

    Let's try some articles:
    While STF does decrease penetration depth, it seems to be due to added weight rather than STF properties. In the second article we can observe that 4 layers of kevlar with STF weigh as much as 16 layers of kevlar (although 16 leyers were not tested) and penetration depth was mostly due to added weight. 4 layers can prevent full penetration yet to decrease depth added mass helps.
  16. Jul 24, 2014 #15
    "Student100" you got it: "...broke his back..."
    As above explained from "ovacs", you need do have decelerating distance for the bullet to be stoped. Here is an example: bullet speed 500m/s and bullet weight 1gr and 2ms stopping time, then the resulting beat to person is 250kg, engough to kill.
    By the way, forget all the different kind of liquids which are discussed above. We are working with loose fibres and may come up soon with remarkable results.
  17. Sep 21, 2015 #16


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    A good link on a STF (not the best but good enough) shot.


    Warning, a 5lb Gummy bear was hurt during the making of the second video.
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