Exploration of Statistical Fatigue Failure Characteristics of 0.063-Inch Mill-Annealed Ti-6Al-4V Sheet and 0.050-Inch Heat-Treated 17-7PH Steel Sheet Under Simulated Flight-By-Flight Loading.
Final rept. Aug 72-Mar 74,
BOEING COMMERCIAL AIRPLANE CO SEATTLE WASH
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A total of 17 mill-annealed Ti-6Al-4V 0.063-in. sheet and 14 heat-treated 17-7PH steel 0.050-in. sheet, unique multidetail specimens were fatigue tested under a flight-by-flight loading spectrum to develop a data base for investigating the statistical materialsstructures fatigue failure characteristics of these two alloys. Columnar buckling restraint was provided for specimens by welded fixtures sandwiching the specimens. A painted crack detection circuit was applied to locate and control size of initiated cracks. In several cases, test specimens of the relatively hard 17-7PH steel fractured before initiated cracks or initial flaws were detected. At open hole structural simulators detected fatigue cracks were removed by oversizing. The initiation data were examined by maximum likelihood methods for both log-normal and Weibull distributional representation. At a 0.50 reliability level, the results did not show an obvious distributional representation. At a 0.50 reliability level, the results did not show an obvious advantage of either distribution, but on increased levels of reliability, the Weibull distribution was a significantly more conservative simulation of the test data, which showed less variability than that estimated in a previous study.
- Metallurgy and Metallography