- Dislocations play a major role in the fatigue crack initiation phase.
- Large number of loading cycles dislocations pile up and form structures called persistent slip bands (PSB).
- 1st stage: PSBs are areas that rise above (extrusion) or fall below (intrusion) the surface of the component due to movement of material along slip planes.
- 2nd stage: tiny microcracks join together and begin to propagate through the material in a direction that is perpendicular to the maximum tensile stress. Eventually, the growth of one or a few crack of the larger cracks will dominate over the rest of the cracks.
Fatigue Crack Propagation Mechanism
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