Failure Mechanism: Fatigue

Fatigue is the weakening of a material caused by repeatedly applying loads.

Three stages to fatigue

  1. Initiation: a crack forms or there is already an existing defect in the material
  2. Growth of the crack
  3. Final failure: when the crack reaches critical size and the material fails

The video illustrates fatigue: the crack continues to grow as the material is exposed to more loading.

Factors affecting fatigue

Crack growth rate can also be greatly increased

  • Oxidation at high temperatures increases the rate of fatigue: grain boundaries are attacked
  • Geometry of specimen: lots of notches provides stresses in the material
  • Environment: erosion and corrosion
  • Temperature: extreme temperatures can decrease fatigue strength

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