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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]

The paper deals with the 3D printing process that is compatible with electrodynamic processing (EDP) of the printed layer in order to increase the density of the latter. Based on mathematical modeling, the influence of the impactor shape for EDP on the stress-strain state of the AMg6 aluminum alloy layer was studied. The formation of residual compressive stresses in the EDP zone was taken as a compaction criterion. The distribution of values along the thickness of the plate of the main parameters and components of the stress-strain state, in particular, the plastic deformation and stress zone dimensions, the depth and width of the contact interaction zone in the metal layer interacting with an impactor roller moving normal to the layer at speeds of 1, 5, and 10 m/s, was determined. The cylindrical impactor with a rounded end surface usage instead a straight quadrangular prism with a rounded side surface formed a higher-density layer, characterized by generation of compressive stresses up to the yield strength of the AMg6 alloy. This helps optimize the structure of the printed metal and increase its durability by forming compressive stress fields in the electrodynamic compaction zone. [ABSTRACT FROM AUTHOR]

The paper deals with the dynamics of asymmetric three-layer hemispherical shells with the discretely symmetric lightweight, rib-reinforced filler under pulsed loads. Since the distances between the ribs are much larger than the dimensions of the rib cross-sections, the theory of independent static and kinematic hypotheses for each layer is applied. In asymmetric shells, the load-bearing layers are made of different materials and have various thicknesses. The equations of motion of asymmetric three-layer spherical shells and natural boundary conditions are obtained using the Hamilton– Ostrogradsky variational principle for the Timoshenko-type shell and rod theory model. This makes it possible to develop an adequate finite element model for asymmetric three-layer shells composed of several materials and obtain numerical results on the dynamic behavior of an asymmetric three-layer elastic structure using the finite element method. The influence of physical and mechanical parameters of asymmetric layers of hemispherical shells on the stress-strain state under axisymmetric internal pulse loading is investigated. New mechanical effects are revealed. [ABSTRACT FROM AUTHOR]

Special features of computational assessment of dimensional change of WWER-1000 reactor core baffle during the reactor operation are discussed. The paper gives results of computational analysis of a change in shape of core baffle, which was performed by applying up-to-date approaches of modeling the irradiation-induced swelling of constrained austenitic steels under the action of neutron irradiation and elevated temperatures. The results have been obtained by using median and conservative values of parameters of the temperature and dose dependence of free swelling of austenitic steel Kh18N10T. The authors have set out the fundamental principles of elastic-plastic stress-strain analysis of the reactor core baffle and core barrel, taking into account the irradiationinduced swelling deformation and contact interaction conditions. The finite-element analysis is based on a FEM mixed scheme that ensures a continuous approximation both for displacements as well as stresses and strains, thus providing a high-accuracy determination of the stress-strain state. The calculations were carried out in the two-dimensional definition for the baffle cross-section with the maximum damaging dose and irradiation temperature in the baffle height, assuming a generalized plane-strain deformation. The calculated results are given for the reactor full-power operation and scheduled shutdown for re-fueling at the end of the charge life. According to the calculation data, disregarding the irradiation-induced swelling deformation leads to an incorrect assessment of the change in shape of the core baffle during its operation, while the use of the accepted free swelling model gives too conservative results on the shape change, even within the designed lifetime. The influence of the mean normal stress on the irradiation-induced swelling of metal makes the principal contribution to the change in shape of the core baffle. During the reactor operation beyond the designed lifetime there occurs a local contact between the core baffle and the core barrel in the zone of the largest-diameter circular opening of the longitudinal cooling channel and the port channel for coolant flow between the baffle and the barrel. The paper gives results of the analysis of the change in shape of the baffle in modeling of the contact conditions taking into consideration the temperature re-distribution due to deviation from the design coolant passage conditions in the zone where the baffle is in contact with the barrel. In the case of using the median dependence of the free swelling, no loss of the nominal gap between the core baffle and the core barrel is observed within the designed lifetime. The computational assessment using the conservative parameters of the irradiation-induced swelling leads to a distinct decrease of the gap between the core baffle and the core barrel and a local contact between them at the end of the designed lifetime. The residual gap between the spacer grids of edge fuel assemblies and the baffle faces is ensured in the case of the median and conservative dependence of the irradiation-induced swelling. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical model for the stress-strain state in a welded joint with a hard single-V butt weld. Analytical expressions for the stress-strain state in both the hard weld and the mild main material subjected to elasto-plastic deformation are proposed. In order to verify the proposed expressions, a finite element simulation of the stress-strain state in a welded joint with a hard single-V butt weld was carried out and the results were compared to the analytical results obtained applying the proposed analytical model. The analytical solution was basically consistent with the finite element analysis results. The proposed analytical model can be used in design practice for assessment of the stress-strain state in welded joints. [ABSTRACT FROM AUTHOR]

The paper presents the stress-strain state simulation of the compound technical structure - vulcanizer diaphragm. A set of working plates in the form of a circular plate with the thickness discretely varied in the radial direction is modeled. An algorithm to solve the contact problem is developed. The obtained calculation results are compared with the experimental ones to demonstrate their practical use. [ABSTRACT FROM AUTHOR]

A computational method based on radial basis functions has been applied to the linear solution of thin plates. This meshless numerical method gives high flexibility in the analysis of irregular geometries, due to its insensivity to spatial dimension. The multiquadrics approach is used in this paper. The numerical solution is compared with Kirchhoff theory for plates. [ABSTRACT FROM AUTHOR]

The paper provides the strength analysis performed for POLYITAN-2 nano-satellite under quasistatic overload conditions arising at the ascent stage. An efficient solid-state model together with its corresponding finite element model has been developed for nano-satellite. The numerical investigation of the stress-strain state of nano-satellite has been performed using the ANSYS software package. The maximum relative displacements of structural elements, as well as safety factors, have been determined. Different strength criteria were analyzed for the strength assessment of nano-satellite structural elements made of composite materials. It is found the considered POLYITAN-2 structure satisfies the critical strength and stiffness requirements. [ABSTRACT FROM AUTHOR]

The paper presents the numerical investigation on the stress-strain state of single- and two-layer spheres with spherically transtropic radially reinforced layers under a centrally symmetric internal explosion. A comparative analysis is made between two widely used methods of modeling the explosive loading. The influence of the reinforcing fiber volume fraction and the alternation of layers on the strength of shells is investigated. [ABSTRACT FROM AUTHOR]

The paper provides a review of the known (from available publications) methods and findings of experimental studies of stress-strain state and strength of multilayer thick-walled anisotropic cylinders under dynamic loading. [ABSTRACT FROM AUTHOR]

A three-dimensional stress-strain state calculation is performed by the finite-element method for precracked Charpy specimens side grooves of different depths. Based on the calculated results, the paper addresses the suitability of various brittle fracture criteria to describe experimental data on fracture toughness of these specimens. [ABSTRACT FROM AUTHOR]

Based on the study of interactions between elements of proposed design and engineering solutions, a unified technique is proposed for analyzing the stress-strain state in joints with a continuous, discontinuous, or a combined bonding layer in components with longitudinally variable geometrical and rigidity parameters, under arbitrary thermomechanical loading. Resolving systems of linear equations are derived, an extent of sufficient discretization of s structure is assessed, and some numerical results are provided. The paper gives recommendations of how to use this technique and demonstrates that it can be efficiently applied to the majority of joint types. [ABSTRACT FROM AUTHOR]

The paper describes a method and main results of a refined stress-strain state evaluation for a welded joint of the hot collector to steam generator nozzle of a nuclear power plant with a WWÉR-1000 reactor, which takes into account a fuller range of the actual loading conditions in operation. In calculations, we considered the stresses induced by uncompensated thermal expansion of the reactor elements. The results of 3D finite element calculations suggest that the level of local stresses in the area of the joint exceeds the metal yield stress. The calculated stresses for the outer nozzle surface agree satisfactorily with the in-situ strain measurement data. [ABSTRACT FROM AUTHOR]

The paper describes a 32-channel system for studying full-scale structures developed with the use of the state-of-the-art components. It provides continuous long-term measurement of strains and temperatures up to $\backslash +\; 350\; deg$C and accumulation and storage of measurement data. The system was used to record the elastic strains and temperatures of a welded joint of the hot collector to the PGV-1000 steam generator nozzle in the period between the preventive maintenances. The measurement results reveal a complex pattern of strain and temperature distribution different from the axisymmetric one. [ABSTRACT FROM AUTHOR]

The effect of the metallic layer thickness on the stress-strain state and strength of metal-composite cylinders of the total constant thickness under internal dynamic pressure produced by the explosion of a charge evenly distributed along its axis in air at the constant total-to-running charge mass ratio (ξ = 1.421 mm was numerically investigated. The strength of the cylinders was evaluated by the generalized Mises criterion. The strength of shells with a unidirectionally circularly reinforced outer composite layer for the composites of low tensile strength in the isotropy plane is shown to be mainly governed by the wave processes across the shell width. Under this condition, its dependence on radial and axial stresses is much higher than on the circumferential ones, which are usually much larger than the first two components of the stress tensor. The four composites and two designs of the cylinders: thin-walled and medium-thickness are examined. The cylinders are double-layered: the inner layer is steel (St20) and the outer layer is a circularly reinforced composite. At given (ξ and the total constant cylinder thickness H, the optimum in strength terms ratio (βopt of the metalliclayer thickness h to H is strongly dependent on H, a composite (i.e., its physicomechanical characteristics) and varies within 0.4–0.7 for thin-walled cylinders and 0.6–0.7 for medium-thickness ones. Irreversible plastic energy losses in the inner steel layer have a significant impact on the shell strength, as a result the shock wave travelling to the outer composite layer is of lower intensity and the strength of the object as a whole can be ensured. The inclusion of the plastic steel layer deformation in thin-walled cylinder calculations significantly changes the dynamics of objects qualitatively but insignificantly increases the strength quantitatively, the Mises strength function can be reduced by less than 5% compared to an ideally elastic calculation. If the plastic metal deformation is accounted for medium-thickness cylinders, it significantly changes the wave patterns both qualitatively and quantitatively, the strength function can be reduced by almost 50% compared to the elastic calculation. [ABSTRACT FROM AUTHOR]

The stress-strain state of a drill string during its compression in a horizontal borehole is considered. The function of the elastic axis of the drill string as a wave curve is obtained, which enables one to improve the analytical models: evaluation of decrease of axial force depending on the drill string elastic axis shape, determination of the force of pressing of the string to borehole walls, and calculation of normal stresses in the cross section of drill pipes. [ABSTRACT FROM AUTHOR]

The authors present the results of computer simulation of the stress-strain state of a thin-walled spherical shell with an elliptical opening and the surrounding reinforcing inclusion of another material. The effect of geometric and mechanical parameters of inclusions on the stress distribution around the opening and deformation of the shell under uniform internal pressure are investigated. The issue of stress concentration in modern leading fields of technology and industry, namely, in mechanical engineering, rocket, and space, is quite topical since it is associated with the reliability and durability of the designed structures or their elements. Stress concentrators can occur due to imperfections in the materials' structure (cavities, cracks, foreign inclusions, etc.) or technological and structural necessity (openings, cutouts, leaks). Shell structures are used as load-carrying structures in many fields of engineering. They combine high strength with low weight, which contributes to their reliability and safety during operation. In most cases, shells in real structures have simple geometric surfaces (shells of rotation). Complex structures are usually a combination of such shells. It is important to investigate the effect of local stress concentrators as openings (considering inclusions) on the stress-strain state of shells. The methods of stress concentration reduction should be outlined. The authors performed a finite element analysis of the effect of reinforcements modeled by inclusions made of the different materials as compared with the shell material having an opening on the parameters of its stress-strain state. Such investigations are crucial for the design and optimization of the structures in many engineering fields. [ABSTRACT FROM AUTHOR]

The effect of two-dimensional regular finite-difference mesh spacings on the accuracy of calculation of the dynamic axisymmetric stress-strain state and strength of hollow composite cylinders of finite length, fixed overall dimensions and thickness has been numerically determined by the Wilkins method modified for helical orthotropy and implemented in an application package, created earlier by the authors. The cylinders were made by a ribbon consisting of VMPS glass fibers, impregnated with an ÉDT-10 epoxy binder, on a technological mandrel. Loading is done by exploding a spherical explosive charge in the center of symmetry of a cylinder in an air atmosphere. The obtained results allow one to choose mesh spacings along the radial and axial coordinates, which ensure an acceptable accuracy of determination of the maximum values of hoop stresses and strains, as well as strength functions by maximum stress and strain criteria and by the generalized von Mises criterion. [ABSTRACT FROM AUTHOR]

Fracture and stress-strain state (SSS) of significantly anisotropic composite cylinders have been analytically and numerically investigated under internal explosion. Four possible types of fracture have been determined, including spallation fracture. The features of wave the SSS and strength of thin- and thick-walled shells as well as the dependence of the maximum permissible critical mass of the charge on the cylinder thickness have been established. [ABSTRACT FROM AUTHOR]

The authors present the calculation results for the stress-strain state of the weldment of the 'hot'collector to the nozzle in the PGV-1000 steam generator in the area of welded joint No. 111 in the simulation of the seismic loading specified using the response spectra for the vertical and horizontal vibrations. The calculation of seismic stresses is performed based on the linear-spectral analysis using the three-dimensional model of the WWER-1000/338 reactor plant. [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]

Results are presented for both the calculated assessment of the residual manufacturing stress fields in the simulation of the heat treatment in the vicinity of welded joint No. 111, and the calculation analysis of operating stresses and the fracture resistance of the collector-to-nozzle welded joint in the PGV-1000M steam generator in the simulation of the operating loading cycle. [ABSTRACT FROM AUTHOR]

Methods for designing structural elements made of structurally heterogeneous materials by developing vectorial models and studying the scale effect of elastic properties have been developed. Results of calculation of stress-strain states with allowance for structural and geometric factors of stress and strain concentration are presented. [ABSTRACT FROM AUTHOR]

For an arbitrary body (a structural member) subjected to external steady temperature and force actions, a limiting state condition which ensures the uniform strength of the body until its load-carrying capacity is exhausted has been derived using Rabotnov's kinetic theory of creep. A procedure of strength analysis of structural members by the limiting state is put forward. For the case where the limiting state condition is fulfilled only on some individual portions of the body's surface, a procedure of calculating its stress-strain state with the nearest approach to the uniform-strength state is outlined. [ABSTRACT FROM AUTHOR]