The calculation of buried large-sized structures for specified seismic impacts should take into account the field of gravity, contact interaction with the ground. The representation of the boundless half-space of the soil by a limited finite element domain requires taking measures to exclude the influence of boundary effects on the solution. The article proposes and analyzes a set of measures to eliminate edge effects: an algorithm for restoring kinematic load according to an experimental seismogram, the use of superimposed grids to separate the waves incident and radiated from the structure, and quasi-dimensional grids with viscosity to dampen waves at infinity. The algorithm for restoring the seismogram is based on comparing the discrete analogue of the experimental seismogram with the results of a one-dimensional problem of the test pulse run in a ground environment and considers the re-reflection of elastic waves in a multilayer soil with a horizontal upper surface and the boundaries of the media. The method of superimposed grids allows to bring the source of seismic impact closer to the foundation of the structure. The secondary interference waves emitted by the structure freely exit to the technical subdomain with a sparse grid, where calculations are carried out using linear viscosity to dampen the wave and noise associated with the numerical dispersion of the solution on the inhomogeneities of the grid. The proposed approach using superimposed grids makes it possible to reduce the time of numerical calculations by orders, since only in the subregion adjacent to the building small grids are set and nonlinear effects (contact interaction, elastic-plastic deformation) are taken into account. The use of quasi-uniform grids with the introduction of linear viscosity will reduce computational costs by two orders in two-dimensional problems and three orders in three-dimensional ones.

The paper investigates the dynamics of a body under a piecewise constant periodic force with an arbitrary duty cycle and in the presence of an oscillation limiter. The mathematical model is a strongly nonlinear non-autonomous dynamical system with a truncated phase space along one of the phase coordinates. Using the point mapping method for strongly nonlinear (vibro-impact) dynamical systems, equations for two-dimensional Poincare map are obtained in the form of explicit analytical formulas. The relations obtained for Poincare map made it possible to effectively study the rearrangements of arbitrarily complex periodic motions with both a finite and an infinite number of fixed points, depending on the change in the parameters of the dynamical system. This allowed us to represent for the first time an analytical form of the equations that define in the parameter space the boundaries of the existence and stability domain of periodic motions with an infinite number of fixed points on the Poincare surface (corresponds to the infinitely impact mode of motion). The numerical experiments presented in the paper using a software product developed in the C++ language made it possible to present bifurcation diagrams that clearly demonstrate the ranges of parameter values with chaotic motion modes of the body. A scenario for the emergence of chaos has been established. The transition of body motions with a change in the overload parameter from periodic motion modes to chaos is carried out according to the period doubling. Comparison of numerical analysis with analytical results for different sets of parameters of the system under study (overload parameter) showed their good agreement.

The methodological aspects of assessing the service life of new equipment (elements of gas turbine engines), the operating modes of which lead to non-stationary thermomechanical loads, are considered. The associated thermoviscoplastic processes of deformation and damage states of the degradable continuum are modeled. A model of thermal fatigue in polycrystalline structural alloys for arbitrary complex deformation trajectories is described, consisting of relationships that determine cyclic thermoviscoplastic deformation; evolutionary equations for damage accumulation and strength criteria for damaged material. Kinetic equations take into account the effects of nonlinear damage accumulation, are based on the introduction of a scalar damage parameter, and are based on energy principles. The related formulation of the kinetic equations for damage accumulation under low-cycle fatigue and long-term strength describes the nonlinear nature of damage accumulation. The criterion for the strength of damaged material is the condition that the damage reaches a critical value. Using the developed original methodological, algorithmic and software that allows for end-to-end numerical modeling of thermal cyclic processes, the problem of assessing the thermal cyclic durability of models of elements and components of gas turbine engines during thermal pulsations has been solved. The results of an analysis of the influence of the angle of inclination of cooling channels in a model of combustion chamber pipes on the thermal cyclic durability are presented. The issues of the influence of complex thermal cyclic deformation, accumulation of fatigue damage, plastic deformations and creep deformations on the thermal fatigue of structural elements are considered. A comparative analysis of numerical results with experimental data was carried out. The efficiency of the model for describing the process of thermal fatigue of materials and structures under multiaxial disproportionate paths of thermal cyclic loading has been confirmed.

A linearized model of prestressed elastic body vibrations is described in terms of the nonsymmetric Piola stress tensor, and a weak statement of the original problem is given. With the help of the Lagrange variational principle, we construct a statement of the problem of steady axisymmetric oscillations of a thin-walled (shell-like) cylinder with variable material properties in the presence of an inhomogeneous prestress field. The motion equations, essential and natural boundary conditions are formulated. Integral characteristics are introduced that average the change in prestresses and material properties over the shell thickness. On the basis of the model presented, the problem on steady-state vibrations of a functionally graded prestressed cylindrical shell is numerically investigated via the shooting method; the influence of the laws of change in material modules and prestress components on dynamic characteristics (e.g., amplitude-frequency characteristics, natural vibration frequencies) is analyzed, a comparative analysis of the solutions is carried out depending on the thin-walled parameter. For the considered cylindrical shell with axial inhomogeneity, based on the acoustic sounding data, we study the inverse problem of restoring two laws of prestress inhomogeneity characterizing the nonuniform initial stress-strain state of tension or inflation. As additional information, we consider the measurement data of the displacement components on the cylinder's surface, given in a set of points at a certain frequency of steady-state oscillations; in such a case, the material characteristics are considered to be known and may depend on the axial coordinate, which makes it possible to set an arbitrary functional gradient along the axis of the cylinder. The mode of probing loading is determined by specifying the traction type and oscillation frequency. Explicit formulas for the desired laws of prestress inhomogeneity are obtained, and computational experiments are carried out to restore them. A high accuracy of reconstruction is revealed far from the ends of the cylinder when probing at a frequency in the vicinity of the first resonance.

The article describes the development of a modification of the Kolsky method used for testing brittle materials at splitting. The scheme of the experiment involves the application of a dynamic load along diametrically opposite generatrices of the cylindrical surface of the test specimen. At the same time, it is in a biaxial stressed state and fracture into two halves from the action of tensile stresses. The method is based on the assumption that the material under test behaves elastically under equilibrium deformation of the specimen. This modification is proposed to be used to determine the dynamic Young's modulus and Poisson's ratio. The derivation of relations for calculating the indicated mechanical characteristics based on Hooke's law using experimental possibilities is given. Approbation of the proposed scheme for determining elastic constants was carried out when testing specimens of fireclay brick in the Hopkinson split bar system. The deformation impulses of measuring bars were recorded with the help of tensometry to assess the forces acting on the sample and calculate the stresses arising in its center. Deformations of the central part of the specimen were determined using digital image correlation technology. The obtained graphs of stresses and strains versus time had a different time step using the optical method in combination with tensometry. The arrays of the obtained stress and strain values were reduced to a single and constant time interval up to the moment of specimen failure using linear interpolation to process the experimental data based on the derived formulas. The study made it possible to construct graphs of the dynamic Young's modulus and Poisson's ratio versus time at the initial stage of specimen loading and to determine the average values of these elastic mechanical characteristics.

The possibility of using non-destructive methods for monitoring the state of silicon carbide materials in friction pairs of pumps of WWER installations has been experimentally demonstrated which makes it possible to identify potential sites of future possible destruction on the working surface of bearings. The paper describes the methodology for studying the acoustic properties and electrical conductivity of products made of silicon carbide composite. The relationship between the electrical conductivity and acoustic parameters of the material of friction pairs of WWER installations with the characteristics of the microstructure of the material under study has been experimentally established. As the hardware part of the emission and reception of acoustic pulses Krautkramer USN 52 device certified by the State Standard of Russia with emitters and receivers of longitudinal and transverse waves was used. To assess the electrical conductivity a VT2 eddy current electrical conductivity meter with a 5 kHz clamp-on transducer was used which has a pointer transducer with a uniform scale not graduated in electrical conductivity units as an indicator device. Measurements of the electrical conductivity and velocity of longitudinal and transverse waves polarized along the radius at the same points of the working surface of the bearing showed the coincidence of the nature of the change in the measurement results. In this case, if the excess of the value of the velocity of longitudinal waves in the fracture zone over the average value for the entire working surface of the bearing is up to 30%, then for electrical conductivity it is 40%. By measuring the velocities of transverse waves with polarization parallel and perpendicular to the radius, the presence in the material of bearings that have not passed tests under conditions of high pressure and temperature of significant internal stresses provoking the appearance of destruction (chips) on the working surface has been established.

The problem of increasing the adhesive strength of plasma powder coatings by introducing a metal bundle from a new composite powder of domestic production into them has been solved. Synthesis of composite powder material is carried out by the method of cladding matrix ceramic particles with a metal component. The results of studies of a new powder material of the composition (ZrO2+8%Y2O3) with a granular composition of 40/80 microns obtained by chemical cladding of zirconium dioxide particles with a nickel shell (30 wt.%), as well as the coating formed from it. The regularities of the formation of an experimental coating from this powder material with a spherical particle shape have been studied using electron microscopy and X-ray diffraction analysis. It is established that a coating with a two-phase composition (T-ZrO2+Ni) is formed during high-energy plasma spraying. In cross-section, the coating is a composite structure consisting of zirconium dioxide grains with nickel interlayers. The coating is characterized by an average hardness of HV(medium) ~ 7,6 GPa and a surface roughness of Ra(medium) ~ 6,12 microns. When micro-indenting, the coating does not show fragility. The scratch test method was used as the main method for studying the strength properties of the coating. During sclerometry, a predominantly cohesive mechanism of coating destruction was established. The destruction occurs by a cohesive mechanism with a violation of the bonds in a thin surface layer and is accompanied by chipping of the microfragments of the coating. The critical load of the beginning of the formation of microcracks (Rs) ~ 10 N and the beginning of the formation of chevron microcracks (Rt) ~ 45 N were determined. The high adhesive strength of the adhesion of the investigated coating to the substrate is shown, since during the tests there is no detachment from the substrate up to the maximum load (200 N). The developed ceramic coating is promising for protection against mechanical and erosive wear of critical parts of power engineering working at elevated temperatures.

The process of suppressing transverse vibrations of an elastic rod spinning in a horizontal plane and fixed at one of its ends is studied. It is supposed that the rod spins around the vertical axis at a constant angular velocity and performs transverse vibrations in the vertical plane, the vibrations are assumed small in amplitude. Transverse vibrations of the spinning rod are performed under external mechanical action. Lateral vibrations are described by the displacement function and considered in a rotating plane by using the classical beam model. The necessary conditions of optimality are derived and applied for suppressing elastic vibrations on a finite time-interval. The problem of optimal suppression of lateral vibrations caused by initial disturbances is formulated as a variational problem with constraints that take into account the suppressing effects on the rod. The limiting restrictions are presented in the form of inequalities. With the introduction of an additional variable, these restrictions are reduced to standard integral equality, while taking into account the energy constraints imposed on the control actions. The proposed iterative algorithm for solving the formulated problem is a numerical-analytical algorithm and consists in minimizing the quadratic quality criterion. This criterion characterizes the vibration suppression process and allows the implementation of improving variations. As a result of the operations carried out, the dependence of the vibration suppression process on the determining parameters, such as the angular velocity of rotation, the isoperimetric energy constant, and the length of the considered process of vibration suppression in time, has been clarified. An example that illustrates the implementation of the proposed algorithm and shows the effectiveness of this method for suppressing lateral vibrations is given.

In the work with the use of nondestructive control methods, the issues of determining acceptable durability or safe resource are considered. It is shown that the design monitoring procedure can be presented as follows: determines the original state zero zone, where the material of the product was subjected to low operational loads; further, with the use of nondestructive control methods, the acoustic parameter is measured (without disassembling the product)., such as the speed of elastic acoustic waves, nonlinear acoustic parameter, difference of velocities with twofrequency sensing, etc.; acoustic scanning of the product's metal is performed, in areas where there have been significant loads, signoff voltages, leading to an intensive accumulation of damage (the destruction of metal leading to cracks); defined zone “N” where the metal state parameter, for which the value is taken, characterizing the difference of the acoustic parameter (the speed of elastic waves, nonlinear acoustic parameter, the difference in velocity in twofrequency sensing) relative to the same parameter in the zone of zero exceeds the established level. The regularities established in the work linking the presence of plastic deformation with the difference in the delays (velocity) of elastic Rayleigh waves at different sounding frequencies at a fixed base between the emitter and the receiver of elastic waves, as well as the behavior of a nonlinear acoustic parameter during the safe resource time, suggest the possibility of using the observd fact as a principle for controlling the limiting state of the material due to plastic deformations on industrial structures. Based on the proposed approach, an engineering methodology for determining the technical condition of the material of the structures of production facilities is proposed, which allows to establish three stages of operation: the reliable operation mode; the controlled operation mode and the critical operation mode.