I know for a ballistic vest, the kevlar fibers are incredibly tough. In a previous life I was an LEO and was the senior range officer for several years. We did a lot of testing on vests, and they were much stronger than you would first think. The guy who developed one of the first commercial brands of vests used to demonstrate his vest by putting it on, then shooting himself at point blank range with a .357 magnum. Having said that, at this point I'll turn it over to the engineers to discuss the strength characteristics of composite materials :-)