PSI - Issue 28

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

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1. Introduction Almost all materials under different temperatures exhibit to some extent creep properties. Creep is observed in structural materials within a specific stress and temperature range. It is necessary to take into account creep behavior of metals under high temperatures. A large number of books, monographs, and review articles (Rabotnov (1966), Kachanov (1960), Boytsov et al. (1997), Shesterikov (1983), Lokoshchenko (2007), Lokoshchenko (2016), Radchenko and Eremin (2004), Arutyunyan (2004), Lokoshchenko (2012b), Lokoshchenko (2014), Arutyunyan (2015)) are devoted to the peculiarities of material deformation under creep conditions. The analysis of publications on experimental study of creep indicates that the research results are significantly influenced by such factors as: the shape and size of specimen cross-section; preliminary plastic deformation of the material; type of stress; adding vibration stress (vibration creep) to static one; presence of microinhomogeneities in material; exposure to aggressive environments. In the fifties of the last century L.M. Kachanov and Yu.N. Rabotov laid the foundations for the approach of mechanics of damaged medium to the description of creep and fracture processes by introducing a damage parameter ω which describes the state of the material from initially undamaged ( ω 0  ) to completely destroyed ( ω 1  ) (Rabotnov (1966), Kachanov (1960)). The works (Lokoshchenko (2012a), Stepanova and Igonin (2014), Stepanova and Igonin (2015)) provide an analytical review of the results obtained using the approaches of Yu.N. Rabotnov and L.M. Kachanov to failure processes under creep conditions with the help of scalar and tensor damage measures. In (Sosnin et al. (1986), Nikitenko (1997)) the authors consider the creep and fracture as mutually affecting each other processes. The value of specific dissipation power is taken as a measure of creep intensity. To describe the third section of creep, relations for the energy responsible for creep fracture and kinetic equations describing the change in the damage measure ω during deformation and damage accumulation were formulated in (Kazakov et al. (1999)). Various versions of creep model modifications (and their approbation on experimental data) formulated in (Kazakov et al. (1999)) are presented in (Kapustin et al. (2015), Kapustin et al. (2008), Volkov et al. (2016a), Volkov et al. (2016b), Volkov et al. (2017)). In (Arutyunyan (2015), Arutyunyan (2017)) the author proposes a version of the theory of creep and long-term strength based on the concept of loosening. Some results on the development and application of computational models of crack propagation in structural elements under creep conditions are reflected in (Wena et al. (2013), Shlyannikov et al. (2015), Abubakker and Sivasambu (2015), Nikbin (2017), Gorokhov et al. (2017)). The creep model (Kazakov et al. (1999)) for studying the creep processes of stainless steels under the conditions of thermo-radiation effects was developed in (Gorokhov et al. (2005), Kapustin et al. (2007)). The authors in (Margolin et al. (2006a)) proposed a physical-mechanical model that describes the fracture of materials exposed to neutron radiation under creep conditions. The physical-mechanical model of fracture (Margolin et al. (2006a)) was applied to predict the long-term strength and ductility of 1Kh18N10T steel in the initial and irradiated state (Margolin et al. (2006b)). An engineering approach to predicting the rate of crack growth in austenitic materials under conditions of neutron radiation and creep based on the fracture model (Margolin et al. (2006a)) was proposed in (Margolin et al. (2006c)). This article presents a description of a numerical technique based on FEM for studying the deformation processes and damage accumulation in structural elements made of heat-resistant alloys under conditions of high-temperature creep with account for the effect of neutron radiation, as well as the results of the numerical solution of problems confirming serviceability of the proposed technique. 2. Technique for numerical study of high-temperature creep of structural elements The description of the material behavior within the proposed method is carried out on the basis of the general model of damaged material (Kapustin et al. (2015), Kapustin et al. (2008)) using the previously proposed thermal creep model for unirradiated heat-resistant alloys (Kapustin et al. (2008)), supplemented with taking into account the effects of irradiation of the materials under consideration in a specified temperature range and radiation intensity. For the alloys under consideration, the most significant effect of irradiation (in the considered temperature range and irradiation intensity) is manifested only in a noticeable change in the thermal creep rate and appearance of brittle fracture effects during creep.