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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Invasive and non-invasive temperature-control systems comprising K-type thermocouples and pyrometry (Zwick/Roell SensorTherm Sirius SI16) were employed before the initiation of the crack growth rate tests and computations. For the purpose of this study, we used a uniaxial extensometer (crack opening displacement (COD) gauge Epsilon 3548-10) with a gauge length of 5 mm to measure the CODs on the outer surface of the sample at the location of the original notch (Fig. 1a). Optical microscopy is used to monitor the evolution of the crack length and crack growth rate on the free specimen flat surface during the tests. 2.1. Loading conditions The isothermal fatigue and TMF crack growth tests were performed in a laboratory environment under stress control at different nominal stress levels under uniaxial loading with a load ratio R = 0.1. Conventional pure fatigue tests were carried out under sinusoidal harmonic loading at a frequency of 0.017 and 1 Hz at isothermal ambient (T=23˚C) and elevated temperature (T=400˚C, 650˚C) . Creep – fatigue interaction CGR tests were implemented in a specially designed the trapezoidal cycle program with the 5-s loading and unloading parts and dwell time of 60 s, which was applied at the maximum load at isothermal elevated temperature (T=400˚C, 650˚C), as can be seen in Fig. 2. Thermo-mechanical fatigue tests were performed with either IP or OOP thermal cycling, and temperatures of 400 – 650°C over a cycle comprising 30 s of loading (heating)/unloading (cooling) periods in triangular waveforms. The heating and cooling rates were 8.3 °C/s. The temperature was controlled using a pyrometer placed at the axial centre of the gauge length on the side opposite the notch. The length of the pre-crack was at least 5 mm, as measured from the notch root.

Fig. 2. Test program for isothermal and thermo-mechanical fatigue conditions.

2.2. Tested material The material considered for the current experimental and numerical investigations was a fine-grain nickel-based ХН73М superalloy. This material is mainly used for discs in the rotating hot sections of aeroengines because of its excellent high-temperature mechanical properties. The chemical compositions and main mechanical properties used in the numerical study for the SENT specimen are listed in Tables 1 and 2.

Table 1. Chemical compositions of XH73M alloy

Element

C

Cr

Ti

Al

Mo

Nb

Ni

Fe

wt.%

0.08

13-16

2.3-2.7

1.3-1.7

2.8-3.2

1.9-2.2

Bal.

<2,0