The present work details a new approach to the study of GTU rotor vibrations, based on the solution of a related dynamic problem for the «gas – dynamic flow – deformable structure» sys-tem. The modern tendency to increase an aggregates power with a simultaneous decrease stiffness results in new phenomenons that affected a rotor vibration state. The compressor rotor model with a labyrinth seal is considered. ANSYS software product is used. The calculations were carried out on a high-performance computer complex PNRPU. The performed calculations showed a qualitative and quantitative effect of a gas-dynamic gap on the rotor dynamics. A 2FSI calculations series was performed to study the influence of geometric, kinematic and gas-dynamic parameters on the rotor dynamic state. A pressure fluctuations spectral analysis in the gas-dynamic gap and displacements has been carried out. The obtained spectrograms pro-cessing it possible to plot amplitudes and frequencies dependences of resonant pressure oscil-lations over an initial pressure in the gas-dynamic gap. It was found that the initial pressure in a gas-dynamic gap has the greatest influence. A rotor and gas oscillations resonant frequency was found, which corresponds to a change in the shaft axis spatial position. The «gas – struc-ture» system resonant frequencies were obtained for models differing in mass and stiffness. A decrease in an elasticity modulus of the structure led to a decrease in the maximum pressure fluctuations amplitude, while a decrease in mass led to its increase. For the base model and the model with lower rigidity, the resonant pressure oscillations frequency depends on the initial pressure value according to a law close to linear, while for the model with a lower mass, the dependence has a pronounced non-linear character.

The paper presents a three-mass rheological model of the system "soil – vibration plate base – vibration plate frame". The rheological model makes it possible to reproduce different modes of interaction between the vibratory plate base and soil: with different types of plate decoupling and without decoupling. We verify this model by comparing the experimental values of the vertical oscillation span of the base and frame of the Zitrek CNP 20 vibrating plate with the previously calculated values. As a whole, the calculated values of the span of vertical oscillations of the base and frame of the Zitrek CNP 20 vibrating plate correlate with the experimental data in the range of the dynamic modulus of soil deformation of 13…30 MPa. During the experiment we used the rheological model and obtained results are as follows: the mass of the vibrating plate (50; 150; 250; 350; 450; 550; 650; 750 kg), the coefficient of the elastic resistance of soil (30; 60; 90; 120 MN / m), and the coefficient of viscous resistance of soil (100; 200; 300 kN • s / m). The total number of combinations of parameters was 96. The processed results of the computational experiment provide the regression dependences for calculating the maximum soil reaction force, the time of soil loading (increasing the values of the reaction force of soil) t1, and the time of soil unloading (decrease the values of the reaction force of soil) t2. The simulation results show that, within one exposure cycle, the soil loading time t1 is less than the soil unloading time t2. The ratio t1/t2 is influenced by the weight of the vibratory plate, as well as the factors of elastic and viscous resistance of soil. This feature (t1/ t2  1) is typical for both vibratory rollers and rammers, which is confirmed by the results of the relevant experimental studies. The obtained regression dependences of parameters Fs, t1, and t2 on the vibratory plate mass and the factors of elastic and viscous resistance of soil are important for calculating the distribution of stresses and strains on the depth of the compacted soil.

The paper analyses the mesostructure of the structural elements of lattice aircraft shells – ribs consisting of alternating layers of equal thickness and made from unidi-rectional CFRP and pure matrix material. In experimental studies, the elastic characteristics of unidirectional CFRP were obtained under three-point bending and transversal compression. As a result, the longitudinal modulus of elasticity of the layered composite turned out to be 101 GPa, and the shear modulus was 2.95 GPa. Numerical modeling of the meso- and micromechanics of the interaction of the noticed layers under transversal compression has been performed up to failure. The ANSYS FEA software (explicit and implicit formulations) was used. The regular and stochastic stacking of fibres in the cross section under compression is considered. The fiber diameters in the composite element were measured on thin sections using a Zeiss Axio Observer D1m digital microscope and were equal to 5.1 ± 0.8 µm. Layers with a fiber volume fraction of about 60 % alternate with layers of pure epoxy. It is proposed to use only the first principal stress in the matrix as a micromechanical criterion for failure under com-pression and tension. At the first stage of calculations, the problem of transversal compression of a cell with a regular laying of fibres was solved (the error in the value of the transversal modulus of elasticity was less than 2 %). At the second stage, an assessment was made of the strength and accumulation of microdamages under compression in a model of a layered structure with stochastic fibre stacking. The analysis of stress-strain state of a layered mesostructure under compression made it possible to explain the reason that the rib has a trans-verse strength twice lower than that of a homogeneous CFRP. The calculated values of the ultimate strength in transversal compression of a layered rib are in good agreement with the experimental ones.

The article evaluates the bearing capacity of the hip joint endoprosthesis made of carbon/carbon (С/C) composites under anatomical load. С/C is made on the basis of carbon fiber Ural N/400-22 and phenolformaldehyde resin novolachny type RP-010. A significant complexity in modeling an endoprosthesis is the prediction of the properties of С/C. The complexity of mathematical modeling based on the mechanics of composite materials consists in the impossibility of experimentally determining the mechanical characteristics of a pyrocarbon matrix. The pyrocarbon matrix does not exist in its pure form separately from the composite material. The mechanical characteristics of the С/C are calculated, mathematical models of bone tissue and endoprosthesis are constructed, taking into account the complex composite structure. The femur is represented by a combination of cortical and spongy tissue. The femur in the study was fixed along the lateral and medial condyles of the femur. This fixation corresponds to the contact spot of the condyle with the lateral and medial menisci. The hypothesis is confirmed that the weakest component in the С/C is the pyrocarbon matrix. The position of the highest values of normal and tangential stresses are revealed. The position of concentration of tangential stresses coincide with the areas of destruction of the endoprosthesis during compression testing, which were previously visually identified. New design and technological requirements for the structure have been identified, which will contribute to increasing the reliability of the endoprosthesis.

The article presents the results of an experiment to study the vibration response of a large-scale reinforced concrete model structure to an impulse load. The load was a series of impacts along the normal to the surface of the element and was applied to all the main structural ele-ments (columns, crossbars and floor slabs). The vibration response was recorded by a system of sensors-accelerometers distributed over the structural elements and synchronized with the accelerometer mounted on the striker. The results of measurements of acceleration vibrograms were saved as digital files. An array of vibrograms recorded by the entire complex of sensors in response to test impacts on the main structural elements made up a vibration portrait of the structure. As a result of processing this information, an array of data was obtained on the propa-gation time of the vibration signal from each signal source to each of the sensors of the registra-tion system (basic array of responses).Key words: Impact localization, accelerometer, The data obtained were used to solve the problem of determining the location of an arbi-trary impact on a structure. To do this, the vibration response recorded by the sensor system during an arbitrary impact was compared with the base array of responses. The comparison was made on the basis of the calculation of the pair correlation coefficients. The resulting spatial distribution of the correlation coefficients made it possible to identify the position of the shock load application. It corresponds to the structural element that has the maximum value of the correlation coefficient. The proposed algorithm was demonstrated on an example where one of the test shocks that participated in the FORMATION of the basic vibration portrait was used as an unknown load. In a numerical experiment using the proposed algorithm, it was found that the accuracy of the impact site identification corresponds to the characteristic step of the structural elements. It is shown that the accuracy correlates with the number of sensors of the registration system and their distribution throughout the structure. The developed algorithm for identifying the place of impact load application can be effec-tively used in the development of automated systems for deformation monitoring.

Ensuring the strength, reliability and safety of structures requires studying the issues of ine-lastic deformation zones occurrence and development which result from equilibrium accumula-tion of damages. Material postcritical deformation characterized by a decrease in the stress level during growing deformations is one of the damages accumulation effects. Application of postcritical deformation theory basic provisions to carry out structures refined strength analysis with additional deformation and strength reserves identification is expedient. Calculation of sof-tening processes stability related to loading systems rigidity is necessary. Consideration of analytical solutions where occurrence and development of softening zones are taken into account is expedient to illustrate main theoretical positions of postcritical defor-mation mechanics. The analytical solution to the hollow cylindrical solid torsion problem where material softening stage and loading system rigidity are considered is obtained. Two-link and three-link approximations of the complete material deformation diagram are considered. Dia-grams of shear stresses distribution over the cross-section are shown; various postcritical de-formation zones development scenarios existence is noted. Loading diagrams are built; torque maximum value dependence on material parameters and rod geometry is defined. The strength and deformation reserves of the structure are revealed. Conditions for complete loading diagram implementation are determined, the loading system rigidity influence is noted. Therefore, ration-ality and necessity of taking into account material softening stage and loading system rigidity in structural design are concluded.

The parameters of the surface microrelief are paramount in the problems of frictional interaction of parts, the flow of liquid and gas in channels, ensuring the required thermal conditions and the stress-strain state of the structure. The solution of the problem of ensuring the optimal thermal regime for a significant range of technical products often becomes decisive in the design of products operating under conditions of high-intensity heat flows. Transit heat fluxes flowing through the product, as well as heat fluxes from own heat sources, must be either accumulated or removed to the external space. In this case, the directions of the heat flux vectors are determined by the design features of the products, including through various contact connections. Obviously, a reliable determination of the parameters of the contact interaction of product parts is the basis for a reliable analysis of the stress-strain and thermal state of a wide range of structures operating under conditions of high-intensity heat flows. The operational characteristics of the contacting parts of the structure are directly determined by the properties of the contact of the mating surfaces. When solving many problems of thermal, mechanical and electrical contact interaction, surface roughness is a major factor. The processes of friction and wear occur precisely on the actual contact area and depend not only on the properties of the material, but also on the intercontact pressure on this area, since the magnitude of the actual pressure determines the destruction of surface films and the appearance of adhesive bonds in the contact. In the presented work, the change in the actual contact area under cyclic loading of contact pairs of materials based on digital twins of contact surfaces in a wide range of compressive pressures is considered.

A mathematical model of electromagnetic thermoelasticity for an initial-stressed transversal-isotropic composite with piezoelectric magnetostrictive phases has been developed. To solve the related boundary value problem of electromagnetic thermoe-lasticity, the Green function method was used as part of a generalized singular approximation of the statistical mechanics of composites, taking into account the initial stress state of the representative domain of the composite at micro- and macro-levels. The solution of the problem of "effective module" for tensors of effective elastic, piezomechanical, magnetostrictive properties, dielectric permittivity and magnetic permit-tivity, temperature, pyroelectric, pyromagnetic coefficients and (which appeared only at the macro level) electromagnetic and magnetoelectric couplings of a quasi-periodic composite with an initial electromagnetic elastic state was obtained. The solutions for the desired tensors of effective properties of the quasi-periodic composite are presented in the form of analytical formulas of simple linear decompositions by solutions for tensors of effective properties of the periodic structure and statistical mixture, decomposition coefficients are the coefficient of "periodicity" (correlation of quasi-periodic and periodic structures) p and "disordering" 1-p, respectively. Results of calculation of all independent components of tensors of effective coefficients of electromagnetic and magnetoelectric couplings of different structures (periodic, quasi-periodic and statistical mixture) are presented in unidirectional direction of fibrous composite "PZT-4/ferrite" with axisymmet-ric tensor of initial macrostrain of composite. For a quasi-periodic composite (with initial macrostrain), the significantly non-monotonic nature of the dependencies of relative (to values in the absence of an initial stress state) values of effective coefficients of electromagnetic and magnetoelectric couplings from the volume fraction of ferrite fibers was revealed. It was revealed that we have an increase in the absolute values of the electromagnetic and magnetoelectric coupling coefficients of composite at negative values of its initial axisymmetric axial macrostrains. The most significant effect is the initial comprehensive macrostrain in the transversal plane on the coefficients of the transversal magnetoelectric coupling of the composite.