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To date, only two models have been proposed for predicting crack growth rates in aircraft engine materials under typical operating conditions. Moreover, modeling to date has been performed on materials which exhibit limited amounts of time-dependent behavior. This investigation evaluates the predictive and interpolative capabilities of these models when applied to IN718, at 649°C. At this temperature, this material exhibits significant time-dependent behavior. Experimental data were generated and used to assess the predictive and interpolative characteristics of each model. These data covered variations in frequency, stress ratio, and hold time. Values for the coefficients in the functional relationships between the constants and the test variables were obtained for the hyperbolic sine equation (SINH) model. Similar functional relationships were incorporated into the modified sigmoidal equation (MSE) model. Several important conclusions were drawn about the capabilities of these two models to predict crack-growth rates in turbine-engine materials at elevated temperature.
elevated-temperature fatigue (materials), fracture (materials), crack-growth-rate modeling, time-dependent behavior
Associate professor, Air Force Institute of Technology, Wright-Patterson Air Force Base, OH
Senior scientist, Materials Laboratory, Air Force Wright Aeronautical Laboratories, Wright-Patterson Air Force Base, OH
Aerospace engineerCaptain, Ballistic Missile Office, Norton Air Force Base, CA