PSI - Issue 13

Elena Fedorova et al. / Procedia Structural Integrity 13 (2018) 741–745 E.Fedorova et al./ Structural Integrity Procedia 00 (2018) 000 – 000

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rate of 2000 °C/min was applied. The maximum stress difference amount to 9% for the case of 30 °C/min cooling rate was observed. It was also found that cooling from 800 °C (1000 °C/min cooling rate) results in practically the same stress distribution as that one calculated when the cooling starts at T = 1100 °C. This implies that a stress level developed at high temperatures is comparably small, apparently because of low elastic moduli and relaxation induced by creep deformation. It should be noted that the stress profile along the y-axis direction is almost identical for all cooling conditions considered.

Fig. 3. Dependence of the minimum principal stresses  3 on the cooling rate

To study the influence of TGO geometry on the stress state, the calculations were performed with the cooling rate of 30 °C/min for the following reasons: i) these cooling conditions were applied in cyclic tests on the blade samples; ii) amongst the all cases, the results of numerical simulation revealed the maximum of compressive stresses and their gradient in the TBO layer. The minimum principal stress distributions calculated for the regular and “ defect ” shapes of TGO layer are presented in Fig. 4.

a

b

Fig. 4. The distribution of stresses in TC, TGO and BC layers after cooling to room temperature with the rate of 30 °C/min: (a) TGO of the regular shape, (a) TGO layer of the “ defect ” shape