The paper considers the modeling of a multilayer nanocomposite, the combination of elements of which gives rise to a spin valve effect. The relevance and importance of effects in the field of spintronics and related materials and devices are described. We study the composition and atomic structure of individual layers of a multilayer nanocomposite, as well as the composition and morphology of the interface of nanocomposite layers. We analyzed a sample with a periodic superconductor-ferromagnet structure consisting of more than 20 alternating layers of niobium and cobalt. The deposition process took place in a deep vacuum. The simulation was carried out by the molecular dynamics method using the potential of the modified immersed atom method. The formation of layers was carried out in a stationary mode. The temperature was adjusted using the Nose-Hoover thermostat. The deposition of each nanofilm ended with a relaxation stage for the necessary stabilization and restructuring of the formed nanocomposite. Three deposition temperature regimes were considered: 300 K, 500 K, and 800 K. For these modes, we analysed the atomic structure of nanofilms and transition regions (interface) formed between the layers. A study of the atomic structure of nanofilms showed that niobium is formed by crystalline regions of different orientations. A cobalt nanofilm is characterized by a structure close to amorphous. The structural features of the interface between the superconductor-ferromagnet layers largely depend on a relief of the surface onto which the deposition is made. The smallest variation in atomic composition is observed in the first niobium-cobalt contact zone, since the formation of the first nanofilm occurs on an even plane of the substrate. An analysis of the influence of the temperature regime during the formation of the nanosystem shows the dependence of the processes of formation of multilayer nanofilm formation, the interface of nanolayers, as well as the composition and morphology of heterostructures on the temperature at which a nanocomposite is manufactured. An increased temperature leads to the formation of a more rarefied structure of nanolayers and an increase in the zones of the interface of nanolayers due to the diffusion of atoms of the sprayed materials.

Many infrastructural concrete facilities, such as dams, bridge footings, foundations of port facilities and offshore drilling platforms, operate in a permanent contact with water. The permeable fractured-porous structure of concrete determines the water-saturated state of the surface layers of such concrete elements. Under dynamic contact loading, the pore fluid is capable of exerting a significant mechanical influence on the local stress-strain state and strength characteristics of the surface layers of concrete. This has to be taken into account when assessing the wear intensity of surface layers and predicting a concrete element’s service life. The aforesaid determines the relevance of the study aimed at identifying the influence of the pore fluid and characteristics of the concrete pore structure on the strength and fracture pattern under quasistatic and dynamic compressive loading. The present work is devoted to the theoretical study and generalization of the laws of mechanical influence of the pore fluid on the dynamic strength of high-strength concrete with a two-scale pore structure. The emphasis in the study is on analyzing the contributions of each of the pore subsystems to the integral mechanical effect of the fluid. To carry out such an analysis, a coupled hydromechanical model is developed. It takes into account the compositional structure of concrete, the presence of a pore space in a cement stone of two different scales, the interaction of a pore liquid and a solid-phase skeleton based on the Bio poroelasticity model, as well as fluid filtration in a pore space. By using the developed model were performed the numerical studies of the dependence between the compressive strength of the representative concrete volumes of the mesoscopic scale on the strain rate, the sample size, the pore fluid viscosity, and pore structure parameters. The simulation results showed the possibility of combining the obtained dependencies into a generalized (master) curve in terms of a combined dimensionless parameter, which has the meaning similar to the Darcy number. We identified two key factors that control the type and parameters of the concrete master curve of the dynamic strength. The first factor is the mobility of the pore fluid in the network of the capillary pores. It determines the rate of stress equalization in the porous skeleton due to fluid flow. The second factor is the interconnection of large micropores with the network of the small capillary pore channels. It determines the magnitude of the decrease in stress concentration in micropores by filtering the excess pore fluid into the capillary pore network. It is shown that the contributions of these two factors to the amplitude of variation of the dynamic strength of the water-saturated concrete are additive, and their total contribution reaches 25 %.

We developed a three-dimensional numerical model of a piezoelectric luminescent optical fiber sensor fixed on a composite’s plate. The computational region of the sensor is the optical fiber with two concentric (with 6 sectors) shells of electroluminescent and piezoelectric materials, two control electrodes on interface surfaces, such as optical fiber-electroluminophore and piezoelectric-cover. The external sensor’s cover is made in the form of a semi-elliptic cylindrical polymer shell, which rectangular base is fixed on the surface of the fiberglass plate. In the piezoelectric shell sectors, the polarization directions of the PVDF transversal-isotropic polymer piezoelectric are different and non-planar for any three sectors. Deformation of the plate causes deformation of the sensor fixed on its surface, as well as the occurrence of informative piezoelectric fields in it, thus the occurrence of informative glows of electroluminescent elements. As a result, we find the requested information about the combined deformed state of the composite plate along the length of the sensor based on the digital processing of the integral intensities of the polychrome light signals at the output of the optical fiber. In simple cases of electric and mechanical loads, we present new numerical results of simulating the distribution of non-uniform electroelastic fields in the sensor multiphase volume, the sensor’s external cover and inside fragment of the composite plate. Loading of the sensor-covering-plate system is performed by controlling electric voltage on the sensor’s electrodes and the plate’s mechanical deformation by stretching along the transverse and longitudinal axes, as well as by twisting around these axes and bending in transverse and longitudinal planes. Numerical values of the control and informative transfer coefficients of the piezoelectric luminescent optical fiber sensor are determined, which makes it possible to perform a reliable and high-precision diagnostics of complex deformations of the composite plates and design sensors of this type.

Wide opportunities of using fine-grained materials as structural and functional materials with advanced physical and mechanical properties have proved the importance of improving the existing technology and creating new processing methods and treatment conditions for such ma-terials. At the same time, a preliminary theoretical analysis using mathematical models gives an opportunity to significantly reduce the cost of such experimental studies. Thus, it is necessary to develop multilevel models of polycrystalline metals and alloys based on crystal plasticity with the description of structure, deformation mechanisms and refinement at various scale levels. To con-struct a correct model of such a class, it is necessary to analyze information and arrange a large amount of experimental data about grain structure refinement. The article presents a review of the experimental studies describing and analyzing the grain structure refinement during severe plastic deformations of various metal alloys. The refine-ment mainly occurs at low temperatures that are a priori lower than the temperatures at which re-crystallization becomes an important factor and the solid-state phase transitions may take place. We have summarized the significant physical mechanisms of the grain refinement during cold deformation based on the arranged experimental data from the review. All the considered articles pay attention to the local accumulation of lattice dislocations inside the grains (in the form of flat clusters), which leads to the lattice curvature and separation of grains into cells. As a result of a further accumulation of dislocations in the walls, there comes an increase in misorientation of the neighboring cells. The curved lattice is unstable (it seems clear that the flat clusters become a source of such curvatures) and relaxes with the formation and movement of the partial disclina-tions, which leads to the rotation of the adjacent grain regions and creation of new grain bounda-ries. In addition, the mesoscale defects located at the junctions of the grains (including the boundary intersection disclinations), flat clusters of the dislocations of the orientational mismatch at the grain boundaries and partial dislocations in the grains have a significant effect on the frag-mentation. The articles about the severe plastic deformation at high temperatures are briefly de-scribed here. It is noted that recrystallization is the main mechanism of the fine-grained structure formation under these conditions. We suggest including the description of the discussed mechanisms in the multilevel con-stitutive material models. When new experimental data appear for a specific process of the severe plastic deformation, the considered refinement mechanisms can be added.

We suggest the phenomenological method of reconstructing the fields of residual stresses and plastic deformations in thin-walled cylindrical tubes made of Х18N10Т steel in the delivery state and after a simultaneous bilateral surface plastic hardening by the vibration-shot blasting of the surface with beads on a special vibrating stand. A cylindrical container filled with three-millimeter beads was attached to it. The tubes were 50 % filled with one-millimeter beads, and they were placed inside the container. The axis of the tube and the container coincided. The space between the tube and the container was 80 % filled with beads. The vibrational frequency of the stand was 18.5 KHz, the hardening time was 20 minutes. The tube in the container was rotated to ensure uniform hardening. We determined the experimental values of residual stresses σθ and σ z in the surface layers using the method of rings and strips with the procedure of the layer-by-layer electrochemical picking of the hardened layers. For this purpose, the experimentally measured values of the beam-strip deflection and the angular opening of the cut ring (changing the diameter) were used. The hardening anisotropy parameter which relates the axial and circumferential components of plastic deformation was introduced into the mathematical model. In solving the stated problems the hypotheses of plastic incompressibility of the material, the absence of secondary plastic deformations of the material in the compression region of the surface layer, as well as the hypothesis of flat sections and straight radii were used. We described the method aimed at solving this type of boundary value problems of reconstructing stress-strain states, which makes it possible to determine the missing component σ r and all the components of the tensor of residual plastic deformations (off-diagonal components of the tensors of stresses and deformations were not considered). The method of reconstructing the stress-strain state is universal, because it has shown its operability both in determining the technological fields of residual stresses, as well as the irreversible strains in the samples in the delivered state after mechanical operations, and after bilateral surface plastic deformation. The adequacy of the calculated data was verified, which was obtained using the phenomenological method of reconstructing the stress and strain fields of the experimental data for the samples in the delivery state and after hardening. The correspondence of the calculated and experimental data was matched. The numerical values are given for the anisotropy parameter connecting the circumferential and axial irreversible strains, for samples, in the delivery state, its numerical value is 0.1, and, for the hardened samples, it is 4.2. This indicates a significant anisotropy of the distribution of the axial and circumferential components of the residual strain tensor. It has been established that the compressive residual stresses are observed in the delivery state in the region adjacent to the inner surface, and the tensile stresses are observed in the layer on the outer surface. Only compressive stresses are observed in both regions after hardening, which significantly exceed in module similar stresses for the samples in the delivery state. The main results are illustrated by the tabular data and the corresponding diagrams of the distribution of residual stresses along the depth of the hardened layer.

The paper presents an experimental methodology aimed at evaluating a very-high cycle resource for aviation titanium alloys Vt-6 (Ti6Al4V) and Ti45Nb for medical applications with different microstructures (large-crystal and submicrocrystalline ones). The submicrocrystalline (SMC) state was obtained by an intensive plastic deformation realized in two ways: the three-dimensional forging for Ti45Nb and radial-shear rolling for Ti6Al4V. The experimental program tests high-cycle and very-high-cycle loading (number of cycles 107-109) realized using the in situ determination method of the accumulation of the irreversible fatigue damage by analyzing nonlinear forms of feedback in a closed system ultrasonic fatigue setup. This makes it possible to establish the connection of the microscopic fatigue mechanisms with the model views and consider the stages of the damage development based on the nonlinear kinetics of the defect accumulation under cyclic loading in high- and gigacycle fatigue modes. We established various relations between changes in the amplitude of the second harmonic of vibrations of the free end of the samples with different internal structures, which are associated with the mechanisms of stress relaxation and damage accumulation. The grain size reduction in Ti45Nb alloy by the three-dimensional forging improved the fatigue properties by 1.3-1.5 times, whereas for VT-6 alloy, the radial-shear rolling method could not increase the fatigue properties in the very high cycle fatigue range, which may be caused by the presence of large residual internal stresses. Based on the scale parameters obtained earlier from the fracture surface morphology and the relations established in this work, the kinetic equations for the origin and growth of fatigue cracks in the gigacycle loading range will be constructed. This equation, based on the empirical power parameters related to the structure of the material, will allow us to determine the number of cycles for the origin of an internal crack and its growth to the surface.