Recent developments in assessing microstructure-sensitive early stage fatigue of polycrystals

• In situ experiments for evolution of microstructurally small fatigue cracks.
• Implications for models of cyclic deformation and fatigue damage in metals.
• Multistage modeling concepts for fatigue crack formation and growth.
• Progressive slip localization and damage formation under cyclic loading.
• Interaction of microstructurally small fatigue cracks with grain boundaries.

Fatigue failure is a leading concern for many applications involving structures for transportation, manufacturing, medical devices, and electronic components. Recent advances in modeling and simulation, coupled with in situ experimental techniques, have enhanced the understanding required to distinguish and characterize mechanisms of fatigue crack formation and early growth at scales of underlying microstructure. In particular, microstructure substantially influences high cycle fatigue resistance and contributes to variability of the fatigue response. This paper reviews the confluence of recent experimental and modeling advances aimed at understanding and modeling of the formation and early growth of fatigue cracks with size on the order of dominant microstructure attributes.