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Spectrum fatigue test results are presented on riveted lap joint and flush joint specimens made from 7075-T6 plate and extrusion and from 7091-T7E69 and IN9021 powder metallurgy (PM) aluminum alloys. For the lap joint specimens, the 7091-T7E69 PM plate material exhibited a shorter fatigue life than the 7075-T6 plate, 7091-T7E69 extrusion, and IN9021 extrusion materials. Crack growth rates were determined for the PM aluminum alloys from characteristic markings made on the fracture surfaces by the modified Minitwist fatigue loading spectrum. Fatigue life predictions were made for two types of 7075-T6 aluminum joints using the local stress-strain method of fatigue analysis. Finite element stress analyses were conducted to determine the local stress and strain at the fatigue critical location of the test specimens due to the spectrum of applied loads. Fatigue life predictions agreed with the test results within a factor of 1.22 for the two types of 7075-T6 specimens analyzed when accounting for the difference in fatigue properties of the materials with respect to grain direction.
riveted joints, aluminum alloys, finite element analysis, fatigue analysis, spectrum fatigue tests, fatigue life, fracture surface markings, crack growth rate, evaluation, powder metallurgy (PM)
Research and development engineer, Lockheed-California Co., Burbank, CA