Effects of frequency on fatigue crack growth at elevated temperature |
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Authors: | Tong,& Byrne |
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Affiliation: | Department of Mechanical and Manufacturing Engineering, University of Portsmouth, Anglesea Road, Portsmouth PO1 3DJ, UK |
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Abstract: | The effects of frequency on fatigue crack growth behaviour have been studied in a prealloyed powder material, Udimet 720Li, at 650 °C. Fracture mode and fatigue crack growth behaviour were studied at frequencies ranging from 0.001 to 5 Hz using a balanced triangular waveform. Tests were carried out under constant Δ K control, with load ratio and temperature being held constant. A mechanism map was constructed where predominantly time, mixed and cycle-dependent crack growth behaviour were identified. The results were verified by SEM analyses. Cycle-dependent crack growth data were obtained at room temperature, while fully time-dependent crack growth data were generated under sustained loads at 650 °C. It was found that mixed time/cycle-dependent behaviour is of most significance for this material at the temperature and frequencies studied. Data for other nickel-based superalloys from various sources in the literature were compiled and compared with those of U720Li alloy at a given stress intensity and temperature in the mixed regime. An analysis was developed to rationalize the observed effect of frequency on fatigue crack growth rate. |
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Keywords: | fatigue crack growth elevated temperature frequency nickel-based superalloys fracture mechanisms |
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