Composite materials based on thermoplastic matrices from LLDPE, PP, and metallic nanoparticles were obtained by the method of mixing in a polymer melt. Methods of thermal analysis and dynamic mechanical analysis were used to analyze thermal stability of the composite materials obtained and their physicomechanical properties are studied. Composite materials of the type under consideration display radiation protection properties against beta-radiation. High correlation of the passing beta-radiation and relative dielectric permeability of the composite material based on the thermoplastic polymer matrices with a metal-containing filler was found.
In the present work we investigate singular effects of the CO2 laser on different ceramic composite mixtures based on boron carbide with addition of different elements. The microstructure of samples at different velocities of laser treatment is compared. The comparison is made of produced microstructures and of ceramics produced by traditional sintering and hot pressing techniques.
Nanofluids, as regards their marvellous enhancement in thermal conductivity, have become useful in several industrial and medical applications. This study presents an analysis of flow, heat and mass transfer for unsteady nanofluid flow through orthogonally moving porous disks. The Buongiorno theoretical phenomena of nanofluids subject to heat and mass transfer of nanoparticles have been designed mathematically for orthogonally porous disks. The fluid is thought to be non- Newtonian, whose flow is described by the mathematical model of a Casson fluid. Governing partial differential equations (PDEs) are reduced to nonlinear ordinary ones which are solved numerically by utilizing the shooting technique. The influence of some parameters on the velocity and thermal distributions with physical quantities like skin friction coefficient, Nusselt and Sherwood numbers has been studied through graphs and tables.
The influence of nanodispersed silver carbonate and microdispersed MoS2 and Mg3Si4O10(OH)(2) fillers on the tribological properties of epoxy composites was investigated. Analysis of the curves of the dependence of temperature and friction coefficient of epoxy composites on the content of the modifier and fillers made it possible to set the optimal weight ratios of additives in a material with improved exploitation characteristics. The wear mechanism of epoxy composites has been substantiated. The process of formation of the lubricant film due to the synergistic interaction of nano-and microdispersed particles with the epoxy polymer was studied; it additionally increases the load capacity and reduces the mass intensity of the wear of composites.
The structure and thermal properties of nanocomposites based on copper nanoparticles in a polyethylene matrix that are obtained by mixing a precursor in the melt have been investigated. Structural changes of nanocomposites depending on the content of copper nanoparticles and properties of a polymer matrix have been identified.
The problem on combined influence of ultrasound and magnetic field on the supersaturated aqueous solution is discussed. It is shown that ultrasound treatment of water in the presence of magnetic field may have a noticeable antiscaling effect at sufficient values of the ultrasonic wave power.
The article investigates the processes of transformation and interaction of defects, such as plane microcracks with linear dimension of the order of 10 mu m that occur in materials when metal samples are treated by short-term pulses of high-density electric current. The investigation is made numerically based on a coupled model of intense electromagnetic field impact on a predamaged thermoelastoplastic material with defects. The model allows for melting and evaporation of metal as well as the dependence of all physicomechanical properties of it on temperature, as was presented in Part I of this article. The solution of the resultant system of equations is sought by the finite-element method on moving meshes, using a arbitrary Euler-Lagrange method. The calculations showed that as a result of simultaneous decrease of the length, release of the molten metal to the crack, and closing of the edges, the crack edges begin contacting the jet of molten metal and, at the end of these processes, the jet is fully enclosed by the crack edges. Thus, the application of current pulses leads to the welding of the crack and the healing of microdefects. In the present work we consider the problems of choosing the preferable integration domains and the conditions at their boundaries when the above processes are simulated. The way in which the processes under consideration depend on the boundary conditions that can be used in the model is investigated. The effect of the distance between the microcracks and of their mutual position relative to each other on the processes of their healing is studied. Numerical simulation showed that in studying the processes microcrack healing it is possible to restrict oneself, without loss of accuracy, to consideration of one representative cell as the integration domain (or one-fourth of the symmetric representative cell) by specifying at its boundaries, that are not the axes of symmetry, the difference of potentials determined for the cell without defect (in the state "unperturbed " by the presence of a microcrack). In such case, the conditions of symmetry can be selected as the mechanical boundary conditions. When the distances between the cracks exceed 5-6 lengths of the cracks, the processes of healing will occur identically, irrespective of whether they are simulated in the integration domain composed of one or several representative cells. Decreasing the distances between the cracks to 1-2 linear dimension of the cracks (taking into account changes in their mutual position) does not change qualitatively the described process of healing; however, this results in substantial slowing down of the process: the release of the molten material to the crack continues, but the decrease of the crack reduces significantly, especially in the lateral direction.
Application of mesenchymal stem cells (MSCs) is one of the most prospective approaches in recovery of damaged organs. Currently, several reasons underlie the limitations of wide clinical use of human MSCs, including their low proliferation rate in vitro. In account of this, searching for new safe and efficient proliferation inducers is an urgent task. In the present study, we investigated the influence of citrate-stabilized cerium oxide (CeO2) nanoparticles on the proliferative activity of human MSCs. Introduction of CeO2 nanoparticles in MSC culture was shown to result in an intensification of cell proliferation rate in a dose-dependent manner. The conducted analysis of the transcription profile of human MSCs in the presence of CeO2 nanoparticles confirmed an increased transcription level for mRNAs of genes responsible for proliferation and cell cycle, as well as suppression of apoptosis. The derived results clearly indicate that CeO2 nanoparticles can be used as a basis for developing highly efficient inexpensive supplement for cell culturing in vitro.
In the present paper, a coupled model of formation of a multilayer coating on the surface of a cylindrical part by deposition from plasma is suggested. The phenomena of thermal diffusion, diffusion heat conduction, mass transfer under the effect of the stress gradient, and of the formation of chemical compounds are taken into account. The rate of coating growth is taken to be a specified function of the velocities and concentration of particles near the surface of the growing coating. The problem is solved numerically. It is shown that during the process of growth the diffusion cross flows, diffusion heat conduction, and thermal diffusion lead to a decrease in the width of the mesoscale transition region between the substrate and the coating. This effect becomes most obvious when the substrate has low thermal conductivity. The account for stresses that develop in the coating-substrate system during the deposition process results in the change of the effective coefficients of transfer and exerts a noticeable effect on the distribution of chemical elements and their compounds in the coating.
The problem of improved simulation of ultrathin rods, arising because of the need of explaining the known experimental data about a substantial dependence of the flexural rigidity of such ultrathin structures on their thickness when the thickness becomes commensurable with characteristic parameters of the material microstructure, is discussed. In order to simulate such effects in the theory of thin rods the gradient theories are used. The question of whether ultrathin structures really implement the scale effects that result in substantial modification of effective rigidity properties is considered. The analysis is made using correct applied versions of gradient theories as well as different approaches in formulating the applied theories of bending of rods, beginning with the variational and semi-inverse methods and ending with the asymptotic method. It is shown that the assertion on a hyperbolic dependence of effective rigidity of ultrathin rods on the thickness, actively discussed in the recent years, is fallacious.
Clinical use of mesenchymal stem cells (MSCs) provides new prospects for treatment of most socially significant human diseases. Meanwhile, today there exist certain restrictions and difficulties in using MSCs for biomedical purposes. One of the restrictions for broad application of MSCs in cell therapy is their low proliferation rate in vitro, which increases the patient's waiting time for such treatment and, ultimately, its cost. Therefore, the search for new efficient and safe stimulators of MSC proliferation represents an urgent problem. In this work, we investigated the effect of cerium oxide (CeO2) nanoparticles on proliferative activity of human MSCs derived from human dental pulp. It was demonstrated that CeO2 nanoparticles are not toxic for human MSCs and increase their proliferation rate in vitro, simulating the level of expression of a broad range of genes responsible for the processes of proliferation, differentiation, and the cell cycle.
Experiments on deposition of barrier and heat-resistant layers were conducted. As the barrier layer (BL) use was made of ZrN that was deposited on carbon-carbon composite material (CCCM) by the method of ion-plasma sputtering. Heat-resistant coatings were applied by the method of atmospheric plasma spraying. A series of samples with the following compositions of heat-resistant layers were obtained in the work: (1) 92 wt.% ZrO2 + 8 wt.% Y2O3; (2) (92 wt.% ZrO2 + 8 wt.% Y2O3) + 10% HfO2; (3) La2Zr2O7; (4) 20% (ZrO2 + 8% Y2O3) + 80% MoSi2, and (5) 10% (ZrO2 + 8% Y2O3) + 90% MoSi2. Also presented in the work are the results of scanning electron microscopy, as well as phase and elemental analysis of the coating obtained. It has been elucidated that the sample with coating of composition (1) has a fine-grain structure pierced by a net of cracks; the sample with coating of composition (2) has only local cracks, whereas that with coating of composition (3) has a large-grain structure with the absence of cracks. The sample with coating of composition (4) also has no cracks and the structure consists of fused particles. This is due to the presence of thermal stresses in the coating caused by the presence of various polymorphic modifications of zirconium dioxide. To stabilize one of these modifications and reduce the stresses that lead to cracking of coating, additives of titanium oxide (2) and of lanthanum oxide (3) were used. The presence of the nanomodified additive HfO2 in amounts of 10 wt.% in coating of composition (2) did not lead to a decrease in thermal stresses, which is seen on micrographs. It is shown that in the samples with coatings of compositions (2) and (3) the microstructure differs substantially, from which the conclusion was drawn that the nanomodifying additive of yttrium oxide increases the plasticity of coating and prevents the formation of cracks. The samples were subjected to testing for heat resistance in an oxygen-acetylene torch flow for 20 s at a temperature 2100 degrees C. It has also been established that coatings of compositions (4) and (5) have excellent operating characteristics and that with increase in the concentration of MoSi2 in a coating, the porosity decreases, the structure of the coating becomes finer, with the average size of the structural component decreasing by 75 nm. Thus, it was possible to attain the self-healing effect with simultaneous stabilization of the monoclinic phase.
The combined influence of generation and coagulation of nanosized critical nuclei on the concentration of nuclei and, ultimately, on the process of scale formation in supersaturated aqueous solutions is considered. It is taken into account that coagulation of nuclei is accompanied by continuous generation and dissolution of them in the bulk water. The estimates obtained showed that the rate of coagulation of nanosized critical nuclei is much smaller than that of their generation. A modified Smolukhovsky formula for calculating the dependence of the concentration of colloidal particles on time n(t) with account for their generation and coagulation is suggested.
An analysis of thermodynamics of CaCO3 phase transition in a supersaturated aqueous solution showed that the formation of scale in the form of calcite on the channel wall in the absence of magnetic treatment of a water flow is related to a smaller Gibbs energy of the generation of the crystalline phase mentioned. Moreover, such a character of CaCO3 crystallization is caused by the fact that the magnitude of crystallographic mismatch between the crystallized salt (calcite or aragonite) and the surface (iron oxide and iron carbonate) is several times higher for aragonite. On considering the process of homogeneous generation in the aqueous bulk, it was found that nanosized nuclei with a radius over 1 nm also had the calcite phase, and those with a radius less than 1 nm have the aragonite phase. This effect was caused by a higher density of the aragonite phase. The results of the analysis of the thermodynamics of CaCO3 phase transition allow one to explain manifestations of the magnetic treatment antiscale effect observed in real-life heat-and-power installations.
In order to model stress concentration near geometrical singularities and the size effect observed in nanoscale media we discuss the implementation of the finite element method (FEM) in considering the linear micropolar elasticity. With the new finite element method developed, few static problems are analyzed where the influence of the microstructure may be important. The provided comparison of the solutions obtained within the micropolar and classical elasticity shows the influence of micropolar properties on stress concentration near notches and contact areas.
In the present paper, modern differential-geometrical methods for modeling the incompatible finite deformations in solids are developed. The incompatibility of deformations may be caused by a variety of physical phenomena, e.g., distributed dislocations and disclinations, point defects, nonuniform thermal fields, shrinkage, growth, etc. Incompatible deformations result in residual stresses and distortion of the geometric shape of a body. These factors determine the critical parameters of modern high-precision technologies, particularly, of additive manufacturing, and are considered to be Ipso Facto essential constituents in corresponding mathematical models. In this context, the development of methods for their quantitative description is an urgent problem of modern solid mechanics. The methods in question are based on the representation of a body and physical space in terms of differentiable manifolds, namely, material manifold and physical manifold. These manifolds are equipped with specific metrics and connections, non-Euclidian in general. All the work as a whole gives a systematic presentation for the geometric aspects of the theory of finite incompatible deformations and contains partial survey of related papers. It is divided into three parts. The present paper represents the first part. It focuses on the physical interpretation of the non-Euclidean structure of the material and physical manifolds. Affine connection on the physical manifold is defined a priori by considerations which are independent of the properties of the deformable body. It is shown that a two-dimensional rigid surface, which formalizes curved substrate used in the deposition process, may serve as an example of non-Euclidean physical manifold. Affine connection on the material manifold represents the intrinsic properties (inner geometry) of the body and is determined by the field of local uniform configurations which performing its "assembly" of identical and uniform infinitesimal "bricks". Uniformity means that the response functional gives for them the same response on all admissible smooth deformations. As a result of assembling, one obtains body, which cannot be immersed in undistorted state into physical manifold. It is an essential feature of residual stressed bodies produced by additive processes. For this reason, it is convenient to use the immersion into a non-Euclidean space (material manifold with non-Euclidean material connection). To this end it is convenient to formalize the body and physical space are in terms of the theory of smooth manifolds. The deformation is formalized as embedding (or, in special case, as immersion) former manifold into the latter one.
A nonlinear model of deformation of a shape-memory alloy (SMA) is presented, discussing characteristics of not only the representative volume, but also individual sets of nano- and microsized martensitic formations in it. This allows taking into account the differences in their behavior in the case of structural transitions (martensitic detwinning and reorientation) and expressing correctly deformations of reverse phase transition, as well as describing the reversing shape memory effect. A simplified model for nanostructured SMAs is proposed. Analytical and numerical solutions of the problem of reversing shape memory for uniaxial tension-compression of a rod, taking into account the structural transition in a change of the load sign and interruption of direct transformation.
The work presents experimental studies of the effect of nanoparticle additives (nanotubes, graphene) on the processes of ignition and combustion of "porous " kerosene in a high-velocity fuel-air stream. The influence of translational nonequilibrium effects on the kinetics of physicochemical processes is analyzed. The impact of explosive atomization effects caused by elasticity of the bubble medium ("porosity ") is investigated. The influence of electrodynamic processes on the hydrodynamics of flame formation in the processes of ignition and combustion is considered. An analysis of the processes of ignition of kerosene with nanoadditives (nanotubes, graphene) demonstrated that a strong change in the flame structure is conditioned by electrodynamic effects, rather by heat effects.
It is shown that the introduction, into a polymer matrix, of filler particles, whose initial dimensions are in the nanometer range do not necessarily lead to the formation of a true nanomaterial (nanocomposite). To achieve this object, a definite structure of the filler in the polymer matrix is required. In the case of nanostructured polymer/organoclay composites, the true nanocomposite can be obtained only on condition there is an exfoliated organoclay structure. The transition from microcomposites to true nanocomposites under other things being equal is accompanied by a great (several times) increase in the elastic modulus.
An efficient process of milling and activation of highly dispersed graphite with the use of the energy of ultrasonic vibrations in the mode of acoustic cavitation in the presence of ammonia, hydrogen peroxide, and iodine has been developed. As a result, the lamellar structure of graphite is split with subsequent deposition of the laminated form of graphite from this dispersion onto the surface of glass, quartz, and aluminum-borosilicate fibers by attraction forces originating between the graphite surface, activated in an alkaline medium, and the glass. This technical solution ensures obtaining and recovering (after the aging of dispersions in aqueous and aqueous-alcoholic solutions) alkali-activated nanosized graphite particles. Ultrasonic treatment improves the properties of dispersions, often called activated colloidal-graphite preparations (CGP). The CGP treated according to the proposed regime, increase the electric conductivity and thermal-shock stability of composite fibers. CGP-coated quartz, aluminum-borosilicate, and basalt fibers can be used for fabrication of volumetric, thermally stable, wide-range, radioabsorbing materials for telecommunication systems of aviation, rocket, and space modules.
