PSI - Issue 28

Vasilii Gorokhov et al. / Procedia Structural Integrity 28 (2020) 1416–1425 Author name / Structural Integrity Procedia 00 (2019) 000–0 0

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( ) ( ) 0 Ф 1 V T FR T П f V R R   

,

( ,Ф)

where R V 0 is the ultimate value of the creep dissipation energy of the unirradiated material subjected to uniaxial stretching; ( ,Ф) FR T is the function that takes into account the effect of the neutron flux Ф on the ultimate value of the creep dissipation energy; (П) 1 f is the function of SSS type (0  (П) 1 f <  ), determined on the basis of approximation, obtained from an experiments on unirradiated material of R V dependence on SSS type. Since brittle creep fracture effects may occur in some heat-resistant alloys subjected to irradiation, it was necessary to make additional changes to the model described above allowing us to account for these effects in terms of alloys behavior. In particular, such a correction was introduced into the brittle fracture model implemented in the UPAKS computing complex (Computing complex UPAKS (2002)) (CC UPAKS) to simulate the fracture processes of unirradiated materials. The description of the effects of brittle fracture in CC UPAKS is based on the kinetic equation for changing the damage measure h ω  (Kapustin et al. (2015)), which makes it possible to represent the development of brittle fracture effects as a quasi-stationary process determined by the relations ω 0   h at R 1 0 σ~ σ  , where 1 σ~ is predicted values of the main tensile stresses (effective stresses); σ σ ( ) 0 0 T R R  are destructive values of effective normal stresses under uniaxial tension; C is the regularization parameter selected on the basis of the "state relaxation" scheme used to implement the computational process when modeling brittle damage. To simulate the processes of brittle fracture of a nickel-based heat-resistant cast alloy under creep and neutron radiation, it is assumed that the destructive values of the effective normal stresses σ ( ) 0 T R becomes a function of the neutron flux Ф and the current value of the accumulated creep strain c k : σ σ ( , Ф, ) Ф Ф c R R T k  . Due to the limited amount of necessary experimental data for the alloy under consideration, the function R Ф σ is represented in the form: (Ф, ) σ σ ( ) 0 c R R Ф k T FH   , where (Ф, ) c k FH is the function accounting for the effect of irradiation on the values of effective normal stresses, depending on the value of the neutron flux Ф and current value of the accumulated creep strain c k . To obtain the above material functions of the model, we used the results of basic experiments carried out at the Research Institute for Mechanics for the considered unirradiated heat-resistant alloy and available experimental data on irradiation creep for this alloy. As a result, the functions ( , τ), ( ,θ) ( ), ( ,θ) , 0 C T l T H T h T c , ( ) 0 V T R , ( ) s T necessary for describing the creep processes of unirradiated material (Kapustin et al. (2008)) were obtained in the temperature range melt T T (0.607 0.679)   , where melt T is the melting point. The functions ( ,θ) FC T , ( ,Ф) FP T , ( ,Ф) FR T , (Ф, ) c k FH , as required for taking into account the effect of irradiation are constructed on the basis of the creep study results for the alloy irradiated with a neutron flux at the temperature melt T T 0.607  . Herewith, it was assumed that in operation, the neutron flux remains constant and does not change in volume. 1 1 0 σ~ σ~ σ  ω   R h С at R 1 0 σ~ σ  ,