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Fatigue Crack Growth in a Rotating Disk Evaluated with the TURBISTAN Mission Spectra Pages: 14 Published: Jan 1989
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View License Agreement Fatigue crack growth rates were generated from four rim cracks in a rotating disk that was evaluated with the TURBISTAN loading spectra. A fractographic investigation revealed the results of correlating variable-amplitude load cycles with fatigue crack striations and that constant-amplitude cycles had been successful in producing marker bands on the fracture surfaces. An annular disk specimen was designed to study the propagation of through-the-thickness radial-edge fatigue cracks. TURBISTAN, which is a standard loading sequence developed for fighter aircraft disk usage, was employed because it provides a more realistic load sequence than the currently used zero-max-zero cycle. The MINITURB version for cold compressor disks was used in this study. An approximate stress intensity solution for a radial-edge crack in a rotating annular disk was developed from two existing solutions by superposition. An aluminum 6061-T6 alloy was selected to provide a readable fracture surface because it striates well. The disk was precracked on a load frame to introduce known discontinuities. It was then evaluated in a spin pit with MINITURB and constant-amplitude cycles. The constant-amplitude cycles were used to create marker bands on the fracture surface to aid a subsequent fractographic investigation. Periodic fluorescent penetrant inspection allowed fatigue crack growth to be tracked. A scanning electron microscope was used to study crack fracture surfaces, correlate MINITURB cycles with fatigue striations, and identify marker bands. Plots of discontinuity length versus cycles and crack growth versus stress intensity are presented. The importance of coupling a realistic mission cycle with the spin pit evaluation of engine disk materials was emphasized. | ||
