Online Archive of University of Virginia Scholarship
Insights Into the Effect of Corrosion Damage on Fatigue and Fatigue Life Prediction Analyses of 7xxx and 2xxx Series Aluminum Alloys218 views
Author
Cocke, Carly, Materials Science - School of Engineering and Applied Science, University of Virginia
Advisors
Burns, James, EN-Mat Sci & Engr Dept, University of Virginia
Abstract
Aluminum aerospace components, commonly made from 7xxx-series or 2xxx-series alloys, experience corrosion and fatigue as primary damage modes. These two damage modes act synergistically. Specifically, corrosion-induced surface roughness acts to cause the early initiation of fatigue cracks during flight. This severely reduces the fatigue life of components and has the potential to cause catastrophic failure. To avoid corrosion-related failures, maintenance regimes use a “find-and-grind” approach to remove corrosion, which can be overly conservative leading to high costs and large aircraft downtimes. This makes understanding the impact of corrosion damage on fatigue and incorporating these insights into maintenance protocols and linear elastic fracture mechanics (LEFM) lifing predictions a necessity. To address this issue, this dissertation conducted three main research tasks.
First, research was conducted on pre-corroded circular through-hole fatigue coupon testing and characterization to understand the impact of corrosion severities and geometry induced stress gradients on fatigue behavior. Results showed that the corrosion severity is secondary to the geometrically induced stress gradients specifically for the galvanically corroded AA7075-T6 samples fatigued in a humid test environment.
The second main research task, broken up into one experimental and one modeling chapter, aims to elucidate the sensitivities of characterized fatigue stages (initiation, small crack propagation, and long crack propagation) and linear elastic fracture mechanics (LEFM) modeling results to different variables and uncover the sensitivities of the experimental and modeling data. The experimental data uncovered the sensitivities of the compared variables to the different characterized fatigue stages. The compared conditions are (1) commonly utilized in lab versus (2) conditions that are harsher or more realistic to in-service environments. The modeling research compared the LEFM modeling results to the characterized sample data to determine the modeling sensitivities to each of the relevant/harsh variables expected in service.
Finally, to advance the understanding of the damage mechanics of microstructurally small cracks (MSC), data cleaning of four crystal plasticity model results was executed. The results showed that the modeling variables (fatigue indicator parameters) do not sufficiently nor comprehensively correlate to the MSC propagation even with extensive data cleaning efforts. The discussion elaborates on why the author does not believe they correlate.
Cocke, Carly. Insights Into the Effect of Corrosion Damage on Fatigue and Fatigue Life Prediction Analyses of 7xxx and 2xxx Series Aluminum Alloys. University of Virginia, Materials Science - School of Engineering and Applied Science, PHD (Doctor of Philosophy), 2026-04-20, https://doi.org/10.18130/d746-7950.
