Originally Posted by silversx80

Ummmm, frames are designed to account for fatigue by designing the frame to not commonly exceed the fatigue limit. BTW, a single stress is not fatigue (i.e. hitting a bump). Repeated cycles are fatigue (i.e. pedaling). The more cycles, the lower the stress limit.

Edit: When fatigue limit is exceeded, materials fail. Plain and simple. It's usually stress fractures or plastic deformation.