Abstract
Assessment of thermo-mechanical fatigue behaviour of the polycrystalline nickel alloy RR1000 reveals a significant effect of phase angle on fatigue life. The current paper explores two scenarios: the first where the mechanical strain range is held constant and comparisons of the fatigue life are made for different phase angle tests; and secondly, the difference between the behaviour of In-phase (IP) and −180° Out-Of-Phase (OOP) tests over a variety of applied strain ranges. It is shown that different lifing approaches are currently required for the two scenarios, with a mean stress based approach being more applicable in the first case, whereas a Basquin-type model proves more applicable in the second. However, it is also demonstrated that the crack propagation phase should also be considered in these types of tests for high strain ranges and projects that future modelling approaches should attempt to unify mean stress, stress range and a crack propagation phase.
Highlights
It is widely acknowledged that thermo-mechanical fatigue (TMF) is one of the most significant challenges facing the gas turbine sector as designers strive to meet the demanding emissions and fuel burn ACARE (Advisory Council for Aeronautics Research and Innovation in Europe) “Flightpath2050” targets
This paper focuses on modelling the effects of phase angle on TMF life in the polycrystalline nickel alloy RR1000
One relatively straightforward approach to ordering TMF results can be made by considering the stabilised mean stress achieved during the test, with the expectation being that an increased mean stress for a constant stress range will lead to a reduction in fatigue life
Summary
It is widely acknowledged that thermo-mechanical fatigue (TMF) is one of the most significant challenges facing the gas turbine sector as designers strive to meet the demanding emissions and fuel burn ACARE (Advisory Council for Aeronautics Research and Innovation in Europe) “Flightpath2050” targets. TMF testing is difficult, expensive and time consuming and there is a wide range of variables that require consideration. Such variables include peak cycle temperature, temperature cycle range, applied strain range, R ratio, phase angle (between thermal and mechanical strains), waveform and applied strain rate. It is desirable that the model, if possible, utilise isothermal data in order to further simplify the input data requirements.
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