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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. [ABSTRACT FROM AUTHOR]

We describe the application of the dual boundary element method for the determination of stress intensity factors in plate bending problems. The loadings considered include internal pressure, and also combined bending and tension. Mixed mode stress intensity factors are evaluated by a crack surface displacement extrapolation technique and the J-integral technique. The boundary element results for the case studies considered in the paper have been compared with either analytical or finite element results and in all cases good agreement has been achieved. [ABSTRACT FROM AUTHOR]

The paper addresses some aspects of inclusion of loading history in the fracture strength analysis of reactor pressure vessels under thermal shock conditions. The strength assessment of a reactor pressure vessel and its lifetime extension are shown to essentially depend on reliability of results of elastic-plastic modeling of stress-strain kinetics and determination of design values of the fracture mechanics parameters. The present findings of the finite-element analysis demonstrate that the loading history must be taken into account in the determination of the temperature dependence of stress intensity factor for a postulated specified crack. It is shown that, in the fracture toughness analysis of a reactor pressure vessel, the temperature dependence of the stress intensity factor has to be derived from the results of the analysis of kinetics and mode of loading of metal at the crack tip under thermal shock conditions. For construction of the above dependence, we proposed approach, which accounts for the active loading and unloading processes occurring in the metal in the crack front vicinity. Incorporation of the loading history into the analysis of the temperature dependence of the stress intensity factor using the proposed approach forcan permit revealing some additional margin of strength during the substantiation of lifetime extension for a reactor pressure vessel under thermal shock conditions. [ABSTRACT FROM AUTHOR]

In this paper, the extended finite element method has been used to evaluate the fatigue life of cracked specimens in presence of bi-material interfaces. The standard finite element approximation is modified by adding appropriate enrichment functions in order to take into account the effect of these discontinuities present in the domain. The level set method is used to track different discontinuities in the domain. The stress intensity factors are calculated by the interaction integral approach. Finally, several numerical problems are presented to demonstrate the effect of these bi-material interfaces on fatigue crack growth. [ABSTRACT FROM AUTHOR]

The paper addresses the use of small-sized specimens of various types, including those with deep (50%) side grooves, for the purpose of fracture toughness prediction. The experimental data for numerous (more than 500) small-sized specimens prepared from materials of various degrees of embrittlement are compared to the test results for full-sized specimens of C(T) type. The concepts of Master Curve and Unified Curve are applied for the processing of experimental data. To handle the test results for small-sized deep-grooved specimens a calculation procedure has been elaborated, which adjusts the calculation method specified in the ASTM Standard E 1921. We provide recommendations of how to use precracked Charpy type deep-grooved (50%) specimens for prediction of a representative temperature dependence of fracture toughness. [ABSTRACT FROM AUTHOR]

Ñurrent calculation analysis approaches to the fracture resistance assessment for main equipment elements of the WWER NPP primary circuit are considered. It is noted that the solution of the problems of justifying safe operation, assessment of the integrity and extension of the lifetime of the reactor pressure vessel is essentially dependent on the results of calculations of the kinetics of the stress strain state, a proper consideration of the residual welding stress and strain fields, reliable evaluation of non-linear fracture mechanics parameters. A general methodology is developed for a calculated analysis of the fracture resistance of WWER reactor pressure vessels in the simulation of emergency cooling conditions. The main statements in the elastoplastic calculation of the kinetics of the stress strain state for reactor pressure vessels are formulated with consideration of the residual welding stress and strain fields, and the calculation procedure for determining the fracture parameters of the postulated crack is presented. Using the calculation methods and software product developed, a significant influence of such factors as consideration of the thermomechanical loading history and elastoplastic deformation of the metal in the vicinity of the postulated crack front, different ways of taking into consideration the residual welding stress level, the regularity and density of the finite element mesh in the vicinity of the calculated crack front, the procedure for calculating the elastoplastic fracture parameters in discrete finite element method models on the calculated fracture resistance assessment of WWER-1000 reactor pressure vessels is shown. It is found that the neglect of the loading history and residual stress level after heat treatment results in a non-conservative assessment of the fracture resistance for the collector-to-nozzle welded joint in the PGV-1000 steam generator in the simulation of the operating cycle of loading. [ABSTRACT FROM AUTHOR]

A modification of a method for the determination of limiting pressure for gas and oil pipelines with corrosion damages of local type under the action of internal pressure and with allowance for temperature field is considered. The problem is solved numerically in three-dimensional formulation. Particular numerical examples illustrate the general design procedure and show satisfactory agreement with experiment. [ABSTRACT FROM AUTHOR]