Fatigue Crack Growth in Several 7050T7451 Aluminium Alloy Thick Section Plates

Author:  S. A. Barter
Source:  Australian Government Dept. of Defence, Defence Science and Technology Organisation
Doc ID:  2003069
Year of Publication:  2003
This is the third in a series of papers that examine material factors likely to influence the fatigue life of F/A-18 structure. Work leading up to these papers has highlighted a number of concerns about the fatigue variability of the 7050 aluminium alloy thick section plate and the effect that the surface condition of finished components has on service fatigue crack initiation and life. This report examines a series of fatigue test specimens that were cut from three different 7050 plates, including two aircraft manufacturer's plates. Following the tests, quantitative fractography was used to produce crack growth curves for each fatigue specimen allowing a detailed interpretation of the crack growth to be made, including a measure of the severity of the flaws from which the main fatigue cracks initiated. Comparisons between previously tested 7050 plate, and the three plates tested here were made, with the finding that the crack growth rates and the flaws from which the cracking initiated were very similar to those previously examined.

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