Carbon fiber snaps.[/quote]Fairly accurate, but simplistic.
cast iron or steel will snap.
cast aluminum snaps.
forged or drawn aluminum (particularly aircraft alloys) will yield/bend up to a point and then snap.
forged or draw steel (particularly chrome-moly) will yield/bend up to a point and then snap.
softer steels and aluminum(s) will weaken with working/bending and then start getting stiffer (see work hardening) followed by snapping.
The force required to break a carbon fiber part (ie bar) is significantly higher than a bar of the same weight made of aluminum or steel. NOTE: Aluminum alloys are generally 2.5 times stronger per pound than steel (this is why many aircraft are made of an aluminum alloy).
Part of the problem of why some carbon fiber products fail is because the designers use the same safety factors as they would for steel or aluminum, ignoring the behavior of the material at its yield or breaking strength. With parts that have no yield strength and their failure is catastrophic, you want a higher safety factor in their design. ie. if you are designing a part made of steel, you might specify a safety factor of 2.5 times the working strength. If you make the same item out of carbon fiber, you might specify a safety factor of nearly 4 times the working strength (and even then, the part would be lighter in carbon fiber).
Yes, a cut in a carbon fiber structure can affect its strength, though it needs to cut the fibers itself. Just nicking the gel-coat surface will not affect the strength.
Some more composite parts:
Wings on an F18 are composite.
Stealth fighter is composite.
Most of Burt Rutans airplanes are composite.
Several new business jets are made of carbon fiber.
Formula race cars have a carbon fiber frame.
The Ferrari Enzo has a carbon fiber frame (including the one that took on a telephone pole sideways at somewhere around 162mph). http://www.wreckedexotics.com/enzo/enzo_20060221_006.shtml
