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

There are 2 ways to stop a bullet: you can catch it, or break it up.

To catch it you use a high tensile strength fabric or other material to catch it like a net. Howver, faster pointier bullets just split through the fibers like a needle.

For fast projectiles you need a hard material to damage the projectile’s tip enough for the fibers to catch it. Steel and ceramic are very good at damaging projectiles, and ceramic is good at absorbing energy by fracturing.

Ultra-high velocity projectiles need to be stopped with spaced armor, such as what’s used on the ISS to protect against meteorites.