PSI - Issue 42

A. Sulamanidze et al. / Procedia Structural Integrity 42 (2022) 412–419 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction High temperature components made of nickel-based superalloys such as gas turbine disc with blades or combustion chamber components are exposed to thermo-mechanical loadings, which can lead to crack initiation and growth. The phase angle between temperature and the mechanical loading varies depending on the structures. Thermo-mechanical fatigue (TMF) data is critical for the generation of appropriate lifing methodologies for a range of in-service applications where non-isothermal conditions are prevalent. The crack growth behaviour under high temperature or thermo-mechanical fatigue is a complex mechanism which depends on a large number of factors, such as creep and oxidisation. One of first code of practice for TMF crack growth rate was done by Stekovic et al. (2020). The effect of phase angle on crack growth mechanisms under TMF conditions experimentally was studied by Pretty et al. (2017), Palmert et al. (2019), Jones et al. (2020) and Norman et al. (2020). The model for the TMF crack propagation prediction have been introduced by Engel et al. (2020). Several studies have addressed the numerical aspects of interpreting the results of the crack propagation rate under in-phase (IP) and out-of-phase (OOP) thermomechanical loading (Ewest et al. (2016), Fischer et al. (2016), Feulvarch et al. (2021)). Karabela et al. (2019) paid special attention to the analysis of oxygen diffusion and crack growth under fatigue-oxidation conditions. However, TMF crack growth rate is still an emerging field and is not yet covered by a code of practice and recommendations for the computations of a test specimen and the crack tip fields analysis. To this end the presented methodology is addressed to in-phase and out-of phase loading cycles in stationary and transient thermo-mechanical fields. 2. Test set up and specimen geometry The test setup included a Zwick/Roell HA100 servo-hydraulic test frame with a Zwick CUBAS control system (Fig. 1a). A Trueheat 10-kW induction heating system is utilised to deliver rapid heating rates through a non-uniform multi turn longitudinal field rectangular coil (Fig. 1b). Rapid cooling rates were enabled through forced air cooling using pneumatic air amplifier with three nozzles. The subject of the numerical and experimental study is a single edge notch tension (SENT) specimen produced from a high-temperature nickel- based alloy ХН73М w ith a rectangular cross section in the gauge (Fig. 1c). Invasive and non-invasive temperature control systems comprising thermocouples, pyrometry (SensorTherm Sirius SI16) and infra-red thermography ( InfraTec ТХ VarioCAM ) were investigated before starting of the crack growth rate tests and computations. The TMF tests were performed at uniaxial loading with a load ratio R = 0.1 at a temperature range of 400°C - 650°C in the cycle including 30 seconds of loading (heating)/unloading (cooling) periods. In order to modelling thermo-mechanical crack growth conditions, the FE computations were undertaken for both in-phase and out-of-phase on rectangular induction heating setup.

Fig. 1. (a) TMF crack growth test setups, (b) rectangular coil inductor and (c) SENT specimen configuration.