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Crack growth rate characteristics in Inconel 718 and a Ti3Al titanium aluminide alloy are compared at 650°C under conditions of cyclic loading and superimposed hold times at maximum load. Whereas a decrease in frequency increases the growth rate in both materials, addition of hold times has different effects in the two materials. Hold times increase the growth rate in Inconel 718, but cause anywhere from a slight increase to a very slight decrease in growth rate in Ti3Al, depending on the cyclic frequency. A simple empirical model is proposed which accounts for crack growth retardation due to creep blunting from hold time effects and considers the environmental degradation of the material with exposure time. The model is seen to provide reasonable capability to reproduce most of the growth rate characteristics observed experimentally while using the stress intensity factor, K, as the correlating parameter.
fatigue crack growth, nickel-base superalloys, titanium aluminides, elevated temperature, analytical model
Wright Research and Development Center, Materials Laboratory, Wright-Patterson AFB, OH
Air Force Institute of Technology, Wright-Patterson AFB, OH