Microstructural Aspects and Damage to Materials in the Gigacycle Regime

At the microscopic level, it seems that the initiation of a fatigue crack in gigacycle fatigue can be generally described in terms of a local microstucturally irreversible portion of the cumulative plastic cycle strain. In one way, there is no difference between fatigue mechanisms in mega-and gigacycle regimes except for the surface strain localization in persistent slip bands in the megacycle case. However, many other specific mechanisms can occur especially at high cycles internally in the gigacycle fatigue regime.