PSI - Issue 59

Eugene Kondryakov et al. / Procedia Structural Integrity 59 (2024) 50–57 Eugene Kondryakov et al. / Structural Integrity Procedia 00 (2023) 000 – 000

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shows the Master curve for 1T С ( Т ), and test results for 0.5T C(T), miniature 0.16T C(T), and side-grooved CT-0.5T specimens. The obtained results showed that the difference between the calculated values of the reference temperature for specimens of different types is not significant : Т 0( 0.5Т) = - 16°С, Т 0(side grooved-0.5T) = - 12°С, Т 0(0.16Т) = - 13.8°С, Т 0(1T) = - 12°С . Thus, the use of miniature specimens makes it possible to obtain correct fracture toughness values while ensuring certain requirements, in particular, the growth of sharp fatigue cracks and increasing the number of tests regulated by the ASTM 1921 standard. 3. Numerical Simulation At present, the strength calculation of critical equipment elements is carried out mainly using the finite element method (FEM). The method is well-established in calculations of resistance to brittle fracture of the 1st circuit NPP`s equipment components Kharchenko et al. (2013), Choi et al. (2019). For this purpose, a structural element with a built-in crack of various shapes and sizes is modeled. At the same time, issues related to singularity at the crack tip remain quite problematic. To achieve the required calculation accuracy the finite element (FE) mesh must be generated with high quality around the crack tip and along the front of its propagation. This leads to some simplification of geometric models during calculation of complex equipment units. Recently, alternative techniques have been developed to avoid such problems. In particular, the submodeling technique is used when calculating complex equipment units (Kondryakov (2022)). Also, one of the promising methods is the extended finite element method (XFEM), proposed by Belytschko et al. (1996) and based on research carried out by Melenk et al. (1996). The method was created to overcome difficulties in solving problems with localized singularities, which are inefficiently solved by classical FEM. The use of the XFEM method makes it possible to significantly simplify the procedure for calculating structural elements with a crack, modeling both a stationary crack (Sun et al. (2023), Bashir et al. (2020), Mora et al. (2019)) and the process of its propagation without additional regeneration of the FE mesh (Muixi et al. (2021), Lin et al. (2017)). In this work, numerical modeling of compact specimens 0.5T C(T), miniature 0.16T C(T) and side-grooved 0.5T C(T) was carried out using XFEM method. Fig. 3 shows the FE models of the specimens. The minimum size of the finite elements at the crack tip is 20 μm. The location and size of cracks were specified by analytical surfaces. For numerical modeling, the true stress-strain diagram for 15Kh2NMFA steel obtained from uniaxial tensile test at room temperature was used (Fig. 4).

Fig. 3. FE models of 0.5T C(T) (a), side-grooved 0.5T C(T) (b) and mini-0.16T C(T) (c) specimens.