Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2023 number 5

The results of a numerical study of the equilibrium parameters of a one-dimensional chain consisting of three dust particles levitating in the electric fields of a gas-discharge plasma are presented. A numerical model is considered in which the motion of dust particles is simulated taking into account the action of the Coulomb repulsion force, external electric field, gravity, electrostatic force induced by the space charge of the plasma, as well as the ion drag force described analytically. A comparison has been made of the spatial distributions of the plasma space charge and potential around dust particles, as well as the equilibrium structural parameters of a chain of dust particles, depending on whether the ion drag force is taken into account analytically or not. It is shown that when the force of ion drag is taken into account analytically, the chain of dust particles as a whole is displaced in the direction of the ion flow. In this case, the distances between dust particles turn out to be smaller than in the case of neglecting the force of ion drag.

The paper described further development of a gas-jet method of synthesizing diamond coatings with the use of a high-velocity jet for transporting the gas mixture (hydrogen, methane, and argon) activated in a microwave discharge to a silicon substrate. A substrate holder is developed, which ensures substrate integrity under thermal loading under conditions of chemical vapor deposition. The diamond synthesis rate in the present experiments is higher than that obtained previously in microwave plasma-assisted chemical vapor deposition experiments without addition of argon.

The generation of a low-frequency low-pressure inductive discharge with ferromagnetic enhancement of the magnetic coupling between the inductor and plasma is investigated. The main features and advantages of this plasma generation method for surface ion-plasma treatment technologies are considered. New experimental data on electrophysical and dynamic characteristics of ferromagnetic-enhanced low-pressure inductive discharge in argon with the addition of oxygen are presented. It is shown that the radial distribution of plasma parameters in a gas-discharge chamber can be controlled using distributed discharge generation. Significant fluctuations in the electron temperature during the period of oscillations of the discharge electric field are found, and the mechanism of their occurrence is analyzed.

A method for measuring the temperature of the silicon melt during plasma-chemical electron-beam refining is proposed. The method is based on measuring the radiation intensity from the melt in the infrared range and comparing it with the temperature. It is established that the refined silicon temperature can be varied from 1500 K to 2600 K by changing the refining conditions, in particular, the electron beam current.

This study demonstrates that the surface roughness of a copper sample can be controlled by treating it with glow discharge plasma. It is established that the main process affecting the morphology and composition of the surface is oxidation. Treatment causes various copper oxide nano- and microstructures on the surface of a copper sample. It is shown that, in the parameter range studied, the working gas pressure has a more significant effect on the formation of various structures than the glow discharge current density. As a result of the treatment, various stages of the surface oxidation are observed, caused by differences in the surface temperature.

Electron beam annealing of a thin film of amorphous silicon suboxide with a stoichiometric coefficient of 0.5 was carried out in a vacuum chamber. The exposure time was 10~min at an accelerating electron beam voltage of 1000 V and a current strength of 75 mA. Using probe measurements and calculations, the transverse distribution of the current density in the electron beam was obtained, which was in good agreement with normal distribution. The current density on the beam axis was 0.8 mA/mm². It was found that the electron beam annealing of the thin film of amorphous suboxide silicon led to the formation of crystalline silicon nanoparticles with a size of (4.1±0.1) nm. The crystallite sizes do not depend on the electron beam current density, in contrast to the degree of crystallinity, which decreases from 40% on the beam axis to zero (amorphous structure) on the periphery. It is assumed that in the process of formation nanocrystalline silicon, a liquid phase is formed.

This paper presents a brief overview of experimental studies carried out at the Institute of Thermophysics of the Siberian Branch of the Russian Academy of Sciences, to investigate the gas dynamics of low-density supersonic jets, including the creation of a vacuum gas-dynamic complex, the development of electron beam and laser methods diagnostics, studies of the influence of viscosity and nonequilibrium effects on the region of free supersonic expansion and the shock-wave structure of underexpanded jets. Problems are considered, and examples of using vacuum stands to model the power, thermal, and polluting effects of full-scale jets of orientation engines on the structural elements of spacecraft and orbital stations are presented.

Specific features of gas flows exhausting from supersonic nozzles to a submerged space under conditions of clusterization are considered. Radiation of particles in the flow is initiated by a well-focused high-voltage electron beam. Radiation is measured by a high-resolution camera and a spectrometer with a wide range of wavelengths. For characteristic sizes of jets of condensing gases in the entire range of examined stagnation pressures and background ambient space, it is possible to use the same dependence on the parameters as that in the case with a correction factor for taking into account the influence of condensation, which, in turn, depends on the cluster size. The form of the correction factor is presented. The dependence of the previously detected process of formation of a secondary external jet in flows of easily condensing gases (“cluster wake”) is studied. The reasons and conditions for the emergence of this effect are considered. The processes of formation of the traditional spindle-shaped jet and the new secondary jet are compared. The results of measurements of the diameters of the traditional and secondary jets in the maximum cross sections by means of photometry in various exhaust regimes are reported. The reasons for the differences in formation of the traditional and secondary jets under conditions of developed condensation of particles are considered. The “cluster wake” is found to affect the process of gas penetration from the ambient space to the supersonic flow. Specific features of radiation of the particles of the “cluster wake” are considered, and the time of existence of radiation in the excited state is estimated.

Supersonic gas flow from an annular nozzle into a low-pressure chamber is studied numerically using kinetic and continuum approaches. Such flows are used in gas-jet plasmachemical technologies based on the use of an electron beam passing through an axial channel. The study is performed by the direct simulation Monte Carlo (DSMC) method and by solving continuum equations using ANSYS Fluent software. It is shown that the solutions obtained are in good agreement with each other even in low-density regions of the electron beam channel. This leads to the conclusion that ANSYS Fluent software is suitable for simulating flows of this type.

Wettability of textured surfaces of copper and carbon substrates is under study. It is revealed that the geometric parameters of the textures being created (e.g., depth and regularity) significantly affect the surface lyophilicity and the manner in which a water droplet spreads and moves. The contact angles obtained experimentally are consistent with the angles obtained via molecular dynamics simulations.

Dimensionless parameters and similarity laws that describe the geometric dimensions of a cermet weld bead formed during direct metal deposition are determined. A VT-6 titanium alloy and ceramics (silicon carbide, SiC) with different volume fractions are used as a powder mixture. A model for estimating the thermophysical parameters of a heterogeneous material is proposed. It is shown that, regardless of the volume fraction of ceramics, the dimensionless geometric parameters of a single track (depth, width, and height) depend on two dimensionless parameters: normalized enthalpy and the Peclet number. Also, these dependences can be approximated by algebraic expressions.

Results of a numerical simulation of an unsteady flow in an axisymmetric intake with internal compression tested in a hotshot wind tunnel with a fixed-volume settling chamber are discussed. The present simulations reveal the main features of various modes: unsteady processes of wind tunnel and intake starting, quasi-steady flow over the started intake with a supersonic flow velocity in the intake duct, and subsequent ulterior transition to the flow with a detached bow shock wave in front of the air intake with a subsonic flow velocity in the duct. A previously unknown mode of the flow over the intake with pulsing motion of the bow shock wave is observed. It is shown that pulsations decay with time, and the bow shock wave position in the incoming flow becomes stabilized at a certain distance from the leading edge of the intake with the test flow in the wind tunnel being preserved.

The problem of instantaneous injection or withdrawal of Newtonian fluid through an injection or production well into an infinite reservoir with a vertical main fracture of constant width at a given constant bottomhole pressure and constant reservoir pressure is considered. Analytical solutions are obtained for the pressure fields in the fracture and reservoir during injection or withdrawal of fluid, as well as for the flow velocity in the fracture. An explicit expression for the fluid leak-off (leak-in) from the fracture into the reservoir (from the reservoir into the fracture) and equations of particle trajectories in in the fracture and reservoir are obtained. For the solutions obtained, graphs are plotted for the pressure fields, fluid velocity distributions in the fracture, and fluid leak-off from the final fracture into a finite reservoir for different reservoir permeabilities.

Direct numerical simulation of interaction between a laminar boundary layer and a shock wave at a Mach number of 1.45 is performed. The influence of a periodic thermal source on the nature of this interaction is described.

The aim of this research to assess the thermal performance of a locally developed two-phase closed thermosyphon system charged with methanol. The performance of the system is examined through experiments to determine the impact of changes in the electrical heat power, liquid charge, flow rate, inclination angle, and cooling water temperature on the output temperature. Temperatures at various points of the heat pipe, as well as cooling water, are recorded. Several fluid loadings are examined, ranging from 4 to 9 ml, which corresponds to the limits of the half full and overfilled evaporator. Different flow rates in the interval 0.2-0.7 kg/min, heat input in the interval 13.0-41.4 W, and cooling water temperature in the interval 15-35 °C are considered. According to the findings, the ideal liquid fill ratio provides the best results in terms of the output temperature, and the heat transfer coefficient is between 64 and 71%. The impact of the adiabatic zone insulation on the temperature distribution along the heat pipe is illustrated.

The effect of a hole radius in an elastic layer on a critical external load at the moment of the onset of fracture, determined by the energy criterion, is investigated. Using the free energy flow through an interaction arc as a fracture criterion makes it possible to describe the dependence of the critical external load on the hole radius. The length of the interaction arc constructed in the vicinity of a free energy peak point is determined using a linear parameter. The introduced linear parameter for a polymethyl methacrylate layer is obtained using known experimental data. The maximum value of the linear parameter can be taken as a material constant.

Based on the Timoshenko beam theory, the vibration properties of a bidirectional functionally graded carbon nanotube reinforced composite beam are investigated. The governing equation of free vibration for the composite beam is derived, which considers the main influential factors, such as the gradient index and the distribution, aspect ratio, and volume ratio of carbon nanotubes. The differential quadrature method is used to solve the governing equation. The natural frequency of the composite beam is obtained. It is found that the natural frequency and vibration mode shapes of the beam are dependent upon the gradient index, nanotube distribution, and volume ratio of nanotubes. However, it should be pointed out that the nanotube distribution in the height direction and the volume ratio of nanotubes have very limited effects on the mode shapes of the composite beam.

In order to study the hardening that occurs during the application of coatings obtained by spraying powder material, experiments were carried out on glass shot blasting of steel test strips using a CCDS2000 detonation complex. Experimental dependences of the cold hardening depth δ and the magnitude of residual stresses σ in the hardened layer on processing parameters (size, density and velocity of particles, strength of the test strip material) were obtained. Engineering formulas are proposed for calculating the values of δ and σ.

A model is proposed for assessing the durability of a bundle of identical fibers under conditions of brittle fracture in the region of tensile stresses located to the left of the Griffiths fracture threshold. It is shown that in the specified stress range, the average durability and the dispersion of durability values increase indefinitely with decreasing tensile stress. Estimates were obtained for the incubation period of durability, its confidence probability and the lower limit of the number of elements of a bundle of identical fibers that guarantee the required durability of the bundle.

Two models are considered, which describe the equilibrium state between an inhomogeneous two-dimensional body with two connected rigid inclusions. The first model corresponds to an elastic body with three-dimensional rigid inclusions located in regions with a constant width (curvilinear rectangle and trapezoid). The second model involves thin inclusions described by curves. In both models, it is assumed that there is a crack described by the same curve on the interface between the elastic matrix and rigid inclusions. The crack boundaries are subjected to a one-sided condition of non-penetration. The dependence of the solutions of equilibrium problems on the width of three-dimensional inclusions is studied. It is shown that the solutions of equilibrium problems in the presence of three-dimensional inclusions in a strong topology are reduced to the solutions of problems for thin inclusions with the width parameter tending to zero.

Using metallographic and ultrasonic pulse-echo methods, studies of the destruction process of St3sp steel under uniaxial tension and fatigue were carried out. Samples were cut from the welded joint, namely from the zone of the base metal and the area of incomplete recrystallization in the heat-affected zone. A comparative analysis of the evolution of rough slip bands in the heat-affected zone and in the base metal was carried out. A connection has been established between the Poisson's ratio, determined by the ultrasonic method, and the mechanical characteristics of the material. Methods have been proposed for estimating the plasticity life under uniaxial tension and the number of cycles before failure due to fatigue.

This paper presents a solution to the Gadolin problem of the evolution of stressed states during the shrink-fit assembly of two cylindrical pipes. The materials of the assembly parts are described using the mathematical model of an ideal elastic-viscoplastic material. The friction law is specified on the contact surface of the materials of the assembly. The yield criterion is taken to be the condition of maximum octahedral stresses (Mises condition) in which the yield stress depends significantly on local temperature. Calculations of time-varying thermal stresses are performed in successive time steps, depending on the temperature distribution reached by that time. The results of calculations of the residual stress and fit interference in the assembly are compared with the values obtained from a numerical-analytical solution of the one-dimensional problem. It is noted that the calculations neglecting the singularity in the boundary conditions predict the different behavior of the fit interference in the near-end region of the structure.