Finite Element Modeling of Fatigue Crack Nucleation in Multi-Phase Microstructures of Aluminum Alloys

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 discretizing microstructural models for finite element analyses of crack nucleation. Digital replications of the microstructure are created from statistically accurate geometry and texture of 7075-T651 aluminum alloy, generated from Scanning Electron Micrographs (SEM’s) and Orientation Imaging Microscopy (OIM). The resulting geometry has two distinct material phases: first-phase grains and second-phase particles. The particles are two to three orders of magnitude smaller than the grains. In order to discretize these models, a previously implemented automated meshing procedure was enhanced with the intent of increasing mesh quality in domains that have excessive variation and gradation in length scales.

Additionally, experimental data has shown that crack incubation and subsequent nucleation occur in and from the second-phase particles. Thus, this work also presents a basis for a probabilistic particle cracking criterion, where the probability of a cracked particle depends on the adjacent grain texture, surrounding stress fields, particle geometry, and number of load cycles. Analysis results for several microstructural realizations are provided in order to demonstrate the stochastic nature of damage nucleation due to the inherent heterogeneity of the microstructure.

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