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

Steel is one single solid structure.

Kevlar is a bunch of special interwoven fibers. Even though they’re strong, there are still ‘holes’ in between them. If something goes fast enough, it can just push the fibers aside and go through the holes.

The steel has no holes, so the rifle bullets just squish it down instead.