抄録
New biaxial thermo-mechanical fatigue testing machine, which can perform thermo-mechanical fatigue (TMF) tests under any selected conditions of axial loading, torsional loading and temperature history with arbitrary amplitude and phase, was developed. TMF tests were performed under complicated axial/torsional loading and temperature waveform (Blade waveform) that simulates strain and temperature histories imposed in actual gas turbine blades, as well as fundamental in-phase and out-of-phase tests. Test temperature was selected between 450-850°C. In case of without strain hold, failure life of the out-of-phase is comparable to that of the Blade waveform, while failure life of the in-phase is longer than that of the out-of-phase and the Blade waveform due to occurrence of negative mean stress. On the other hand, the largest life reduction was observed in the in-phase condition by introducing 6 minutes strain hold at the maximum temperature. Thermo-mechanical fatigue lives under various conditions were well correlated to uniaxial isothermal fatigue data by the equivalent total strain range, Δεeq proposed in this study. Then, time dependent TMF life prediction model was proposed based on the nonlinear damage accumulation model incorporating with Δεeq and failure lives of the Blade waveform with strain hold were accurately predicted by the TMF life prediction model.
