Analysis of Secondary Cracking Behavior in Fatigue Tested Aluminum Alloy 7085-T7452
Date
2022-08
Authors
Blazanin, Scott
Major Professor
Advisor
Collins, Peter C.
Bastawros, Ashraf
Chumbley, Scott
Johnson, Duane
Pathak, Siddhartha
Committee Member
Journal Title
Journal ISSN
Volume Title
Publisher
Altmetrics
Abstract
High strength aluminum alloy 7085 (AA7085) in the T7452 temper is a promising material for use in structural aerospace components owing to its impressive mechanical properties, low density, and good corrosion resistance. However, in fatigue loading under certain orientations, AA7085 has exhibited atypical crack branching behavior, leading to limitations on its use. Expanding on prior work to study the fatigue crack growth rate in this alloy, the current study characterizes secondary fatigue cracking events which nucleate along the primary crack front and often propagate parallel to the direction of loading. Secondary crack metrics were quantified for as-tested plate specimens of two orientations and four loading conditions. Optical image mosaics were used to extract the length of secondary cracks and their placement along the primary crack. It was found that the length and severity of secondary cracking increases with primary crack length for both orientations and all loading conditions. Additionally, secondary crack metrics were compared to fatigue testing data to correlate secondary cracking events with measured stress intensity factors. Secondary cracking behavior was found to vary with loading condition, with high stress amplitude tensile-tensile loading contributing to an increased severity of secondary cracking over a short range of stress intensity factors. Electron backscatter diffraction was used to characterize interactions between secondary cracks and the underlying microstructure, showing that secondary cracking occurs along grain boundaries with high misorientation angles. Kernel average misorientation mapping was used to show a difference in the local fracture mode of secondary cracks, with cracking along high misorientation angle grain boundaries being shown to behave in a brittle manner.
Series Number
Journal Issue
Is Version Of
Versions
Series
Academic or Administrative Unit
Type
thesis