Abstract
Microstructural damage and subsequent failures resulting from thermo-mechanical fatigue (TMF) loading within the temperature range 300–700 ∘ C are investigated for the polycrystalline nickel superalloy, RR1000. Strain controlled TMF experiments were conducted over various mechanical strain ranges, encompassing assorted phase angles, using hollow cylindrical test pieces. The 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 appropriate in the second.
Highlights
During the take-off, cruise, descent and landing cycle that jet engines experience when in service, high temperature features such as disc rims typically endure severe alternating thermal and mechanical loads
This paper considers a number of lifing approaches to determine the effects of phase angle on ThermoMechanical Fatigue (TMF) life in the polycrystalline nickel alloy RR1000
In order to relate isothermal behaviour to TMF, the lives of the tests are normalised by the fatigue life of an isothermal fatigue test on the material at R = 0, ε = 1% at peak cycle temperature (700 ◦C), and a positive or negative effect of the TMF cycle on life can be demonstrated
Summary
During the take-off, cruise, descent and landing cycle that jet engines experience when in service, high temperature features such as disc rims typically endure severe alternating thermal and mechanical loads. Under such situations, cracks can potentially nucleate and propagate to failure, through a phenomenon which is known as ThermoMechanical Fatigue (TMF). Several material properties including creep and fatigue are used to assess design lifetimes of high temperature components such as turbine discs Many of these mechanical properties are obtained from isothermal tests as testing under TMF conditions is difficult.
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