Issue 61

V. Shlyannikov et alii, Frattura ed Integrità Strutturale, 61 (2022) 46-58; DOI: 10.3221/IGF-ESIS.61.03

assist cooling, compressed air flow directed towards the specimen through three nozzles was used, positioned circumferentially with equal angular spacing and the same distance to the specimen, as well as at the same vertical position as the notch. All tests were controlled and monitored using a dedicated TMF software, which automatically performs a pre test procedure, involving thermal stabilisation, thermal strain measurement and validation. The Zwick/Roell HA100 setup is displayed in Fig. 2. The creep–fatigue interaction tests were performed on the test stand of UTS-110MH-5-0U equipped by highprecision crack opening displacement extensometer and a high-temperature three-zone oven (Fig. 3).

Figure 2: Pure fatigue and thermo-mechanical fatigue test equipment.

Figure 3: Creep-fatigue interaction test equipment.

This study presents interpretation and evaluation of a range of isothermal and non-isothermal experimental crack growth data generated by four type tests carrying out by stress-controlled fast and slow harmonic fatigue, creep-fatigue interaction and in-phase (IP) thermo-mechanical fatigue (TMF) conditions as it shown in Fig. 4. Tests on both C(T) and SENT specimens are carried out under loads sufficiently below the yield stress of Ni-based alloy with an initial fatigue crack obtained at room temperature. The pure fatigue tests were performed at ambient 23 ˚ C and elevated temperature 150 ˚ C, 650 ˚ C and 750 ˚ C with an applied nominal stress asymmetry ratio of R = 0.1 under sinusoidal harmonic loading at a frequency of 1.0 and 10.0 Hz. The creep–fatigue interaction crack growth rate tests were carried out at elevated temperature 450 ˚ C, 550 ˚ C, 650 ˚ C and 750 ˚ C with the same stress asymmetry ratio of R = 0.1 in a specially designed the trapezoidal cycle program with the 5-s loading and unloading parts and dwell time of 120 s, which was applied at the maximum load, as can be seen in Fig. 4. The TMF in-phase test parameters employed for the single edge notched specimen is a triangle waveform with asymmetry ratio of R = 0.1 at a loading frequency 0.014Hz over a 400 650°C temperature range with heating and cooling rates at 10°C/s.

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