PSI - Issue 52

Valery Shlyannikov et al. / Procedia Structural Integrity 52 (2024) 214–223 V.Shlyannikov,A.Sulamanidze,D.Kosov/ Structural Integrity Procedia 00 (2023) 000 – 000

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1. Introduction Even though fatigue crack growth mechanisms in nickel base superalloys under isothermal conditions have been extensively studied in the past, there is at present very limited investigations related to the governing mechanisms and patterns for a wide range of thermo-mechanical load conditions, which is necessary for the efficient development of next generation gas turbine material. The crack growth behaviour under high temperatures is a complex mechanism that depends on a large number of factors, including creep and oxidation. However, over the past decade, extensive research has been devoted toward numerically and experimentally analysing the crack initiation and crack-propagation behaviours of nickel-based superalloys under separate loading conditions like pure harmonic fatigue (Gayda and R. V. Miner (1983), Onofrio et al. (2001), Pineau et al. (2016)), creep-fatigue interaction (Narasimhachary and Saxena (2013), Ro et al. (2021), Garnadt et al. (2022)) and thermo-mechanical fatigue (Stekovic et al. (2020), Palmer et al. (2019), Pretty et al. (2017), Jones et al. (2020), Norman et al. (2020), Segersall and Deng (2021), Kitaguchi et al. (2013), Karabela et al. (2013), Xu et al. (2019)). These studies, however, are incomplete with respect to transient thermal and mechanical crack tip field analyses. Thus far, only a few experimental studies have analysed the coupling effect of isothermal and non-isothermal and mechanical loading profiles on crack growth behaviour. Accordingly, the present study aimed to analyse the interplay of the mechanical properties of the material and the applied isothermal and thermo-mechanical cyclic loads combined with the crack growth rate characteristics. In this way, general aspects of crack growth rate at elevated temperatures are considered and their contribution assessed by comparison of pure harmonic fatigue, creep-fatigue interaction as well as in-phase and out-of-phase thermo mechanical fatigue cases. This has given new knowledge regarding patterns of crack growth at elevated temperatures relevant for both isothermal and thermo mechanical load conditions. Numerical and experimental studies at elevated temperatures are conducted on single-edge-notch tension (SENT) specimens of nickel-based ХН73М alloy, which is widely used in the production of GTE turbine rotors. 2. Test set up and loading conditions The test setup for isothermal and TMF experiments included a Zwick/Roell HA100 servo-hydraulic test frame with a Zwick CUBAS control system (Fig. 1a). A Trueheat 10 kW induction-heating system was utilised to deliver rapid heating rates through a four-turn longitudinal field rectangular inductive coil (Fig. 1b). Further, rapid cooling rates were achieved through forced-air cooling using a pneumatic air amplifier with three nozzles. The subject of the numerical and experimental study was a SENT specimen composed of the high-temperature nickel-based alloy ХН73М, with a rectangular cross-section in the gauge section (Fig. 1c).

(a) (c) Fig. 1. (a) Crack growth test setups, (b) four-turn longitudinal field rectangular inductive coil and (c) SENT specimen configuration. (b)