Development of a Gigacycle Bending Fatigue Test Method

Abstract

A vibration-based bending gigacycle testing methodology is introduced as a means to efficiently assess high cycle fatigue (HCF) performance of vibrating turbine engine components. The gigacycle bending test is a modification to a conventional vibration-based approach which was developed to generate bending load conditions similar to those that would cause turbine engine blades to fail under HCF. It was necessary to accomplish two goals in this framework: first, attain a 10X increase in frequency from the conventional vibration-based test frequency so the testing time required to accumulate 10 9 cycles could be accomplished within 20 hours; second, optimize the excitation supply source so fatigue failure strain amplitudes for 10 7 cycle failure could be achieved. Frequency was increased by optimizing the geometry of the test specimen with an iterative finite element process, and the excitation source was changed from the electrodynmamic shakers used in conventional testing to a piezoelectric shaker. The new gigacycle vibration-based fatigue test setup was studied by testing Aluminum 6061-T6 specimens to understand the effects of clamping and the piezoelectric shaker capability. The gigacycle fatigue regime was not achieved because multiple lower cycle tests (10 7 ) were necessary to refine and modify the experimental procedure. Nonetheless, the fatigue results and experimental information gathered shows promise for future application of the test methodology.