Ultrahigh Cycle, High Frequency Fatigue
We have developed a unique capability for high temperature fatigue testing in the kHz frequency range for characterization of the refractory-rich metallic and CMC materials. The high temperature fatigue apparatus consists of a load line connecting a series of components tuned to 20 kHz, including an ultrasonic converter that provides a controlled sinusoidal displacement and an ultrasonic horn that amplifies the axial displacement. This assembly is located within a hydraulic load frame that can superimpose static loads. Testing can be conducted on conventional fatigue specimens or on small sheet samples using a carrier specimen that resonates, imposing a displacement on the thin specimen attached. This system has been utilized for high cycle fatigue testing of Ni-base single crystal specimens at temperatures up to 1000˚C with samples as thin as 150 μm. Various heating approaches have been utilized, including induction heating for larger samples and microtorch approaches for small sheet samples.