Testing of a Fracture Mechanics-Based Criterion for Fatigue Crack Incubation in 7075-T651 Aluminum Alloy Microstructures

Michael Veilleux, Cornell University

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As part of a larger effort to model accurately damage evolution at multiple length scales in high strength aluminum alloys, this work focuses on implementing microstructural finite element models to simulate fatigue crack incubation in the 7075-T651 aluminum alloy. The microstructure geometry of this alloy has two distinct phases: grains and constituent particles. Incubation is particle cracking. Previous work developed a fracture mechanics-based, probabilistic criterion for fatigue crack incubation, where the probability of particle cracking depends on the adjacent grain texture, surrounding stress fields, and particle geometry. In this study, multiple finite element models of microstructures with incubated cracks are generated as accurate replications of microstructures observed through Scanning Electron Microscopy (SEM) and Orientation Imaging Microscopy (OIM). For each of these observations, the stress fields in a region containing the microstructure are known at the time of incubation. The incubation criterion is being tested by applying these stress fields as boundary conditions to the finite element models and then observing the combinations of microstructural geometries, textures, and stress fields inside and surrounding the particle that cause incubation.

Abstract Author(s): Michael Veilleux, Mu Liu, Anthony Ingraffea, and Paul Wawrzynek