Effectiveness of Bullet Proof Vests against other attacks

[Majin Gojira]

I know there are a lot of different varieties of Bullet Proof Vests, so I'll keep the question rather broad and general:
Everyone knows that Kevlar vests are not very effective against knives and the like, which is one of the reasons military grade ones have metal/ceramic plates (depending on the era). But how do both vests (Kevlar and higher up) handle blunt force trauma from, say, a baseball bat or someone's fists?

[Shroom Man 777]

Kevlar vests do not use ceramic plates to protect against knives, but to significantly boost protection against assault rifle rounds.

[TheBlackCat]

I thought the whole point of bullet proof vests is to protect against the blunt force trauma from a bullet. Stopping a bullet from penetrating is easy, the hard part is stopping it from smashing your internal organs. Thus they are designed to spread the impact over a wide area. They are not designed to deal with continuous, sustained stimulus like knives (specialy bulletproof vests with metal mesh are needed for that), but a quick punch or something would probably have the force distributed over the whole torso like a bullet's force is.

[Spetulhu]

I can't speak for Kevlar vests as I use one with Polyethylene as ballistic protection.

The vest is a Class II, not rated against knives. It will protect against punches and such, as the material is thick and somewhat rigid. You'd risk hurting your hand by punching me.

[Pablo Sanchez]

I thought the whole point of bullet proof vests is to protect against the blunt force trauma from a bullet.

You thought wrong, the primary purpose of the "bulletproof vest" is to prevent the bullet from penetrating the body. The vast majority of damage from gunshot wounds occurs as a result of this penetration, leading to blood loss, tissue damage, organ failure, etc. Conversely, the actual momentum transfer or "blunt force trauma" of a bullet is miniscule, sufficient to cause a nasty bruise or fracture a bone but certainly not to kill. Think about this critically: say a man is shot in the chest. In case one, he is just wearing a shirt. The bullet punches through his sternum and shreds his heart, and he's dead before he hits the floor. In case two, he's wearing a vest with no trauma plate. The bullet can't penetrate the kevlar, and he's left with a big, angry bruise on his chest, maybe even a cracked sternum, but his insides are still intact.

[aerius]

But how do both vests (Kevlar and higher up) handle blunt force trauma from, say, a baseball bat or someone's fists?

Feels about the same as a good baseball catcher's chest guard. It'll take a solid punch connecting just right to cause any real pain. A ballbat on the other hand is a bit too much, it'll still cause broken bones with a good swing or if the guy takes a good windup before spearing you with the one of the ends. With ceramic plates I don't know, they should distribute the force better but I suspect you can do some damage with a ballbat.

[Gunhead]

If you can't cause the hard plate to deform, you're just pushing the entire plate against the targets torso, which isn't going to cause significant damage.
Maybe little bruising directly under the impact area.
All hard armors are backed by soft armor and a trauma liner. I don't see how much damage could someone do through all that padding.

According to NIJ standard, armor is considered effective against an attack if the shockwave pattern left on the gelatin used in testing is less than 5cm deep. This being of course after the armor has stopped the bullet.

-Gunhead

[wilfulton]

I actually watched in Iraq some guys hitting each other with an Iraqi police club (think of it as a short baseball bat) while wearing their interceptor armor with SAPI plates. From the appearances, I don't think it could have hurt them that bad, and there were some big guys swinging (of course it goes without saying that the SAPI plate says "handle with care" on the inside, and hitting it with a bat will probably degrade its ballistic protection over time).

I tried to put a knife through an interceptor vest (it had already been destroyed by an RPG explosion, so no loss. While I didn't give it a very hard jab, my knife only penetrated about two layers of kevlar, with at least twenty to go.

Older kevlar vests (namely the flak vest) are not proof against knives. Someone did actually bet his life that the vest would stop a knife. His friend stabbed him and killed him. Interceptor vests are supposedly a bit better, but they're still made of layers of kevlar, which can be defeated individually by a sharp object if swung with considerable force.

The SAPI plates are, I believe, constructed of boron carbide ceramic, which is extremely hard. You'd wreck your knife trying to stab through it.

I guess the answer you're looking for is that the soft armor may or may not stop a knife, and while it may pad against blunt force trauma, it won't give you a whole lot. Hard plates (i.e. Small Arms Protective Inserts) will stop knives, blunt force (barring of course it being sufficient to crush the hapless victim's rib cage), and rifle bullets.