COMPARISON OF SHORT AND LONG FATIGUE CRACK GROWTH IN 7075‐T6 ALUMINUM

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Abstract
The fatigue crack growth rates of physically‐short cracks (0.5 ≤a≤ 1.0 mm), intermediate cracks (1 < a≤ 2 mm) and long cracks (7 < a < 25 mm) were compared using SEN type tensile specimens in 7075‐T6 aluminum alloy with load ratios, R, of 0.05, − 1 and 0.5 under constant amplitude testing at room temperature. It was found that the short cracks grew much faster than long cracks based on applied δK with da/dN≤ 10−7 m/cycle. Even the intermediate cracks grew faster than the long cracks below 10−7 m/cycle. The transition crack lengths where similitude with δK existed was between 1 and 2 mm. Mean stress effects were similar for R= 0.05 and − t, but R= 0.5 caused increased crack growth rates. The above differences are partially attributed to crack closure effects. Based upon plastic zone sizes, LEFM was justifiable with all the experiments.

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