Fatigue (material)

Fracture of an aluminium crank arm. Dark area of striations: slow crack growth. Bright granular area: sudden fracture.

When a material starts to become weakened, because of heavy use, this is known as material fatigue. As an example, a screw may be able to hold an object that weights a metric ton. When it is used for an object that weights only 100 kilograms (220 lb) one hundred times it may start to wear out and show signs of fatigue.