Fatigue is the weakening of a material caused by repeatedly applying loads.
Three stages to fatigue
- Initiation: a crack forms or there is already an existing defect in the material
- Growth of the crack
- 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