Assessment of Fatigue Behavior of Advanced Aluminum Alloys Under Complex Variable-Amplitude Loading

The Federal Aviation Administration (FAA), Arconic, and Embraer have partnered in an effort to evaluate several emerging metallic structures technologies (EMSTs) through full-scale tests and analyses. The focus of this paper is a supplemental test program that is being carried out by the FAA and Arconic in support of the full-scale panel tests. The full-scale fixture is capable of executing complex variable amplitude spectrum loading; however, it was not considered practical for this program to run a full-scale fatigue or damage-tolerance test under such conditions. Instead, an equivalency approach using M(T) fatigue crack growth specimens was conducted to determine an equivalent constant amplitude loading in the axial direction that can be used in a test to accurately represent the complex flight loads. It was also of interest to determine whether to include the once-per-flight compressive load simulating landing in the spectrum crack growth M(T) testing. The special test method employed, results of the equivalency testing, and a comparison to the full-scale panel test results are covered.