Fatigue -

Fatigue in product structures results from repetitious stresses over the object's life. It can occur in metals, plastics, rubber, composites, or other materials. Causes include physical, temperature, chemical, or solar stresses. Breakage occurs during handling, from weight-caused strain, tension compression, or inadequate hardness and structural fatigue of housings and mounting mechanisms.

Examples of Fatigue caused product failures:

• Battery retaining clips under continuous pressure over time finally make contact with other circuitry and cause an electrical short.
• Food containers that can burst or crack when a grocery shopper piles too many items on top of them.
• Opening and closing a laptop lid gradually fatigued (and broke) the hinge because it was easy to over extend the opening motion thus applying unanticipated stress on the main hinge structure.