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Corrosion Pit to Fatigue Crack Transition Methodology for AA7075-T651 Aluminum Alloy

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Technical Report

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U.S. Air Force Academy USAF Academy United States

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Corrosion damage pit is a stress raiser that can have deleterious effects on the fatigue life of airframe structural components. A better understanding and method for modeling the corrosion pit to fatigue crack transition would greatly help the aircraft community. This paper presents the development of a standardized fatigue test method for the determination of the transition of a corrosion pit to fatigue crack in aluminum alloy AA 7075-T651 specimens. The standardized test method requires the development and validation of several sub-protocols 1 a pitting protocol to create a mechanically small 200 micron diameter corrosion pit on the hole edge of the fatigue specimen 2 a spot welding protocol for attaching the direct current potential drop dcPD probes on either side of the corrosion pit for fatigue crack growth measurement 3 a dcPD fatigue test method applying a unique 10-4-6 marker band sequence to measure the fatigue crack growth and 4 a crack growth life prediction protocol using AFGROW. AFGROW simulations are used to predict the crack shape evolution during the test. New stress intensity factor SIF solutions for small finite width plates with different crack shapes are being developed and validated with the pit-crack test sample for more accurate crack growth predictions.

Subject Categories:

  • Mechanics
  • Properties of Metals and Alloys

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