The fuselage skin itself isn't necessarily strong enough to withstand the beating from ice shedding from the props, so on the Dash 8 it is re-inforced with kevlar panels. Next time you look at the aircraft, you will see a patch that looks like a welded panel fixed onto the fuselage inside the props on each side. This is the kevlar protective layer, and on some aircraft you can even see the various dimples and small dents where ice has struck this panel over a period of time.