Jean-Charles Stinville¹, Patrick Callahan², M. P. Echlin¹, Marie-Agathe Charpagne¹, A.T. Polonsky¹, Valery Valle³, I.J. Beyerlein¹, T. M. Pollock¹; ¹University of California, Santa Barbara, ²Naval Research Laboratory, ³Institut P' - UPR 3346, CNRS - Université de Poitiers - ENSMA

Fatigue crack initiation is governed by the early localization of plasticity during cyclic loading and the transition from plastic localization to damage. High-resolution digital image correlation (HR-DIC) is used to measure the early localization of strain and then Tribeam tomography of the same region captures the sub-surface 3D microstructures that govern damage accumulation. These advanced experimental techniques are used to elucidate the processes that lead to crack initiation during low cycle fatigue at room temperature for nickel base superalloys. A slip redistribution mechanism is observed during the first fatigue cycle, where a complex evolution of the distribution of strain localization near specific twin boundaries occurs. The slip redistribution is present prior to the formation of persistent slip bands and ultimately leads to crack nucleation.