Evaluation of Early Fatigue Signatures in Lightweight Aluminum Alloy 7075
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The current work investigates early material changes that manifest in aluminum alloy 7075 subjected to fatigue loading. Tension-tension specimens linearly tapered in width were exposed to cyclic loading with compliance and eddy current measurements made in-situ, while nano-indentation, surface potential, x-ray diffraction, and ultrasonic response were made ex-situ. Early stage damage progression was evaluated at various size scales and used to estimate a remaining life in real time. Baseline, in-situ, and post failure measurements were compared and analyzed as a function of fatigue cycles. Eddy current and compliance measurements showed a strong correlation between signal strength and fatigue life with eddy current providing a more precise signal per specimen. Microscale electrical measurements showed a link between surface potential and regions of the specimen that experienced higher tensile stress. Results are discussed with an emphasis on multiscale damage detection and identification due to fatigue cycling, while highlighting the most promising techniques for improving structural durability and real-time state monitoring.
KeywordsFatigue Eddy current Ultrasound Nano-indentation Non-destructive testing Damage precursors
The authors wish to thank Mr. Scott Grendahl for help with specimen preparation as well as Mr. David Gray with experimental set-up and data collection.
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