why can’t kevlar stop rifle bullets even though it’s strong than steel on an equal weight basis?

Question

Ar500 steel plate can stop rifle bullets. In my brain I’m thinking like “well if kevlar is stronger than steel, then slab of kevlar of the same size of an ar500 plate should stop rifle bullets too”. Clearly it doesn’t and I don’t understand why

In: Engineering

Answer 1

Thin, pointy, and fast pokes a better hole than thick, blunt, and slow.

Try poking your finger through a sheet of paper and then try a pencil.
Most rifle projectiles are pointier and smaller in diameter.

Now add the velocity to the equation.
Rifles tend to utilize more powder due to a larger casing. More powder, more fast (there are also different powder burn rates at play here)
Their casing is bottle necked, increasing the pressure. Gases escaping smaller hole means higher pressure.
The projectile is sometime lighter than that of a pistol projectile. Lighter objects are easier to move.
This is how you can get rifle rounds that will move 3X the velocity of a pistol round.