Date of Award

12-2017

Degree Type

Thesis

Degree Name

Master of Science in Aeronautics and Astronautics

Department

Aeronautics and Astronautics

Committee Chair

Michael D. Sangid

Committee Member 1

Weinong Chen

Committee Member 2

Alberto W. Mello

Abstract

Brittle constituent particles play a significant role in the fatigue of 2xxx series and 7xxx series aluminum alloys. This thesis contributes new knowledge of physically small fatigue crack growth in AA7050-T7451 3/4 inch rolled plate. In-situ fatigue crack growth imaging with x-ray synchrotron computed micro-tomography (μXSCT) is used to observe and quantify in three-dimensions tortuously propagating fatigue cracks interacting with constituent particles. An empirical relationship is shown between the surface area of a constituent particle and crack path deflection distance. An analysis using a linear elastic model for the Eshelby inhomogeneity and the Westergaard crack tip indicates the stress concentrations developed by constituent particles may contribute to crack path deflections. This finding has implications for modeling fatigue crack growth in AA7050-T7451 rolled plate. In addition, a μXSCT approach to visualizing fatigue crack closure effects with tomography data using local thickness mapping of the crack void is evaluated. The results estimated crack opening load to be around 50% of the maximum load and this compared well to other experimental techniques in the literature.

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