The Effect of High Altitude Environments on the Dislocation Structure Evolution During Fatigue Cracking of Legacy and Next Generation Aerospace Aluminum Alloys
Technical Report,15 Aug 2016,14 Aug 2019
University of Virginia Charlottesville United States
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Next generation structural integrity management of airframe fatigue damage can increase accuracy and reduce over-conservatism by coupling the substantial progress in understanding and modeling mechanical loading spectra with similar efforts to capture the strong influence of an environmental spectrum. Recent efforts have quantitatively demonstrated orders of magnitude reductions in the fatigue crack growth rates dadN for testing in high altitude environments e.g. low temperature and low water vapor pressure PH2O pertinent to high altitude flight. Critically, despite a constant exposure parameter PH2Ofrequency, differences in dadN are observed between tests at 23 degrees C and low temperature environments below -30 degrees C. The main objective of this project is to gain an understanding of the factors governing the environmental cracking behavior via characterization of the dislocation structure in the near crack wake regime of an aerospace Al alloy 7075-T651 at different environmental conditions.