Published: Jan 1990
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The early stage of initiated fatigue crack propagation from a notch root is investigated. The fatigue crack initiation and dependency of growth rates on initial flaw sizes were tested by using compact-type specimens with a keyhole notch in 7075-T6 aluminum alloy. Each of the specimen keyhole notches was indented with a probe with the included angle at the tip of 30, 45, or 60 deg, machined out of a tempered drill rod. Special attention is given to the transition crack length where small crack growth merges into a long crack growth under constant load control at room temperature. Measurements from scanning electron microscopy and macroscopic measurements made by a traveling microscope showed that the short crack growth is dependent on the initial flaw size, load ratio, and the material characteristics. The transition crack length between short crack and long crack behavior is found to be about 1 to 2 mm.
fatigue, fatigue crack growth rates, notches, flaws, small cracks, indents, transition crack length, linear-elastic fracture mechanics, load ratio
Assistant professor, University of Washington, Seattle, WA