Application of Modern Approaches to the Numerical Modeling of the Stress-Strain State for the Strength Assessment of Complex Units of the NPP Primary Circuit Equipment. Part 2. Extended Finite Element Method

Abstract

Along with the classical finite element method (FEM), other calculation methods for assessing crack resistance characteristics are currently being actively developed. This is due to the existing shortcomings of the FEM caused by the dependence of the calculation results on the density of the finite element mesh. One of the promising methods being developed in world practice is the extended finite element method (XFEM), which allows obtaining satisfactory calculation results while simplifying the crack modeling procedure and saving calculation time. In this paper, three problems are numerically modeled using the classical FEM and XFEM methods: calculation of a disc crack in a cube under uniaxial tension, calculation of the off-center tension of a compact CT specimen, and calculation of a cylindrical part of an NPP reactor vessel with a semi-elliptical crack under thermal shock. The obtained results showed that the extended finite element method gives sufficiently accurate results compared to analytical solutions and the classical FEM. At the same time, using the XFEM method does not require considering the singularity of stresses at the crack tip when building an FE model. Therefore, the minimum size of the FE can be increased by almost five times while maintaining the accuracy of the results. This greatly simplifies the procedure for constructing the FE mesh, reduces the total number of FEs in the model, and saves computational time. Thus, the XFEM method can be used to calculate the crack resistance characteristics and improve the efficiency of assessing the resistance to brittle fracture of structural elements.