I mean, it’s designed to stop a bullet which delivers much more force than a human being can ever produce during stabbing
In: 784
Ok.
Take a piece or cardboard and place it on a piece of meat.
Then hit it with a hammer and stab it with a knife.
Which do you recon will break through the cardboard and damage the piece of meat?
—
Note: I know fuck all about guns, so if I get a term wrong keep in mind: I’m not an American, I speak English as 2nd language and I’m an mechanical engineer.
Now this doesn’t mean that cardboard will protect you from getting hit by a hammer. It just means that those two have different kind of impact profile. And therefor the deliver force differently.
A bullet meant for stopping soft targets – as in humans – shouldn’t be sharp. This seems counter-intuitive at first but it isn’t if you follow the logic I presented earlier.
Lets imagine you have a bullet that is more sharp; like a medical blade or an injection needle but bigger. And lets pretend this can somehow survive the forces that would result in it being shot. What would happen when it hits a person? It would basically just go through. It is sharp enough not to pull tissues but cut through them. It would actually do very minimal harm all things considered. It doesn’t deliver force but rather pushes through with it
Now if you consider some small calibre bullet, like under 9mm. You look at the tip, it is rather round or at time it has 0 sharpness,as it is flat (used for target shooting if I’m not mistaken); or “negative sharpness” as in it is concave “hollow point”.
So why is that? Why would “negative sharpness” be desirable quality? Because you want the bullet to deliver as much kinetic force to the target as you possibly can. It is this force that stops people. It is this force that causes massive destruction inside the human body as it causes a shockwave that destroys our more fragile organs. But in reality even this is actually lot of the time undesirable – you don’t always want to kill but you want to stop or disable otherwise. Imagine getting kicked or hit to the stomach so that it knocks the wind out of you. You are helpless and unable to act for tens of seconds, even minutes.
—
So what is the difference between these two types of protective gear?
One is made of fibre that resists laceration, as in the individual strains are tough and the weave is made tight so that it is hard to get even a sharp object in to it, to even cause a cut to start. It doesn’t have to stop the blade, just ensure that it doesn’t go through to your skin.
The other is made of fibres the stretch and deform without breaking, and from a flexible weave that once they meet a fast flying object, they slow it down draining energy. In only has to slow it down enough to ensure that the bullet doesn’t penetrate your skin. The bullet can and usually does go through the fabric, but it has lost enough energy to not go through your skin or damage your organs. It’ll still hurt like hell and bring you down. In reality bullet proof vests are made by stacking these fabrics or top of each other and/or impact plates. Depending on what level of resistance is desired. But whatever method(s) are used, the point is still the same: Slow down the kinetic object so it doesn’t penetrate.
Now we use the methods used for stab resistance and bullet resistance for other things also. When making explosion resistant structure for industrial use, blasting, or even high pressure handheld water jet operation (Hydrodemolition – aka really powerful power washers). Or when protecting wires and cables in machinery; or people who work with sharp objects or machinery in industry and construction who need laceration resistant PPE. The design principles remain the same.
Latest Answers