Metal Fatigue

Metal fatigue is a mode or mechanism of failure during which the stress applied to the device is alternating.  Alternating stress is stress that changes with time and can be accompanied with high frequency.  Different types of alternating stresses can include: 1) push-pull-push-pull, 2) bending up, bending down, bending up, and 3) vibration, among others.  When metal fatigue occurs, a crack is initiated at a point of high stress and/or stress concentration.  At any point during the stress cycle, the crack may grow or extend and each time it does so, a striation or "birth mark" is left to denote the growth.  Photograph A is a scanning electron micrograph (SEM) showing fatigue crack growth from lower left toward upper right at a magnification of 10,000x.

Photograph A Scanning electron micrograph showing fatigue crack growth from lower left toward upper right at a magnification of 10,000x.

Cases involving Metal Fatigue:
Chemical Plant Accident

Articles about Metal Fatigue:
Taking the Mystery out of Metal Fatigue (Pt. 1)
Taking the Mystery out of Metal Fatigue (Pt. 2)
Taking the Mystery out of Metal Fatigue (Pt. 3)