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A comparative analysis of the main types of greases and base oils for their manufacture that are used for lubricating mechanisms operating in space is performed. Their differences in terms of chemical composition, volatility, and operating temperature range are analyzed. The research results on the tribological properties of lubricating greases and on the effect of the base oil and additive types on their life are presented. The main techniques for testing the volatility, the lubricating ability, and the life of greases are reviewed.

The results of the tribological properties studies of composite materials at cryogenic temperatures are presented in the present paper. Test equipment has been developed, friction and wear tests have been carried out at a temperature of T = - 196 °C. The test results showed a significant dependence of the composite material wear rate on the load.

This paper presents the methodology and test results of rolling bearings of low-flow electric pump units used to ensure circulation of the thermal liquid in the active thermal control system of spacecraft. A multi-position stand has been developed for testing bearings within 40 days in a thermal liquid at a speed of 6000 rpm with the possibility of registering the separator rate speed. As a performance criterion, the clearance in the bearing is used. The conditions of the onset of pitting are investigated.

This article presents a methodology for the study of the relative lifetime of lubricating greases operating in rolling friction. An experimental assembly is described for testing lubricating greases in order to determine the friction coefficient and relative resource. A criterion for assessing the relative resource of lubricating greases has been proposed. The test results of the proposed method were obtained and presented.

This research paper presents the results of studies of the tribological properties of materials manufactured using the “KARBUL” technology, modified with powders of various compositions. The tests were carried out according to the “disk-disk” friction pair on a modern friction machine SMT-1. The structure and wear mechanism of materials manufactured using the Karbul technology have been investigated.

An attempt is made to summarize studies of the erosion-corrosion wear fracture of materials, which proceeds by a complex mutually determining mechanism. Parts of submersible pumps and pipelines of nuclear power plants, as well as members of shutoff gate valves, which are subjected to this mode of fracture are considered. Basic methods and test equipment used in the experimental studies are described.

The purpose of the presented work is to increase the lifetime of space mechanisms bearings. The authors reviewed the studies of the bearings and linear mechanisms operating in air and in vacuum. A testing equipment is developed to assess the lubricity and lifetime of greases in the air. Criteria for the evaluation of relative lifetime are defined. Four types of space greases are tested.

The effect of additions of nanostructured tungsten carbide powder into a sinter mixture with compaction of sintered hard alloy VK8 on its tribological properties has been studied. Physicomechanical properties of the material obtained have been estimated. The produced hard alloy shows elevated wear resistance to abrasive wearing.

The study deals with tribological properties of the nanostructured WC-12%Co coatings deposited by the detonation method. It is found experimentally that their wear resistance depends on the concentration of monocarbide WC. The dependence of the WC concentration in the coating on deposition conditions is obtained. The microstructure of the coatings, their physical-mechanical properties, phase composition, porosity, hardness, and modulus of elasticity are studied. The advantage of the nanostructured coatings over the coatings deposited from micropowders is shown.

The problem of hydraulic fracture formation in a porous medium is investigated in the approximation of small fracture opening and inertialess incompressible Newtonian fluid fracture flow when the seepage through the fracture walls into the surrounding reservoir is asymptotically small or large. It is shown that the system of equations describing the propagation of the fracture has self-similar solutions of power-law or exponential form only. A family of self-similar solutions is constructed in order to determine the evolution of the fracture width and length, the fluid velocity in the fracture, and the length of fluid penetration into the porous medium when either the fluid flow rate or the pressure as a power-law or exponential function of time is specified at the fracture entrance. In the case of finite fluid penetration into the soil the system of equations has only a power-law self-similar solution, for example, when the fluid flow rate is specified at the fracture entrance as a quadratic function of time. The solutions of the self-similar equations are found numerically for one of the seepage regimes.

For a set of comblike polymers manufactured by polymer-analogue conversions, nonlinear optical and photosensitive properties are investigated. On the basis of the chemical modification, the interaction between polyamidoimides with side carboxyl groups with glycidyl ethers of commercially manufactured azo dyes (DR-1, DO-13, DY-7) is used. It is shown that transparent films of these polymers have a reasonably high electrophotographic photosensitivity (at a level of 104 cm2/J), and the coefficient d 33 of second-harmonic generation describing nonlinear optical properties is within 4.5–6 pm/V.

Depressurization of high-pressure vessels filled with a liquid coming to the boil with a decrease in pressure is investigated. After depressurization, which takes less than 1 ms, a rarefaction wave propagates into the vessel. Experiments [1–5] demonstrated that the pressure behind the wave goes over to a constant value, which is independent of the vessel diameter and lies between the saturation point and atmospheric pressure. The correspondence between the experiments and different bubble formation theories (bubble formation on the vessel walls, due to rupture of the bonds between the water molecules or boiling on foreign particles) is analyzed. A “ mechanical nucleation” theory is proposed, in which it is assumed that the liquid comes to the boil on a limited number of foreign particles, and the bubbles formed on the nucleation centers undergo multiple fragmentation due to the instability developing under the action of centrifugal accelerations of the bubble surface in the course of bubble growth. The calculations demonstrated that, after depressurization, bubble fragmentation occurs at the vessel outlet. Due to the growth of the phase interface in the course of fragmentation, the boiling intensity increases, the pressure grows, and a shock wave propagates into the vessel, following the rarefaction wave. Multiple fragmentation of the bubbles occurs on the shock front. This wave is followed by a series of waves with smaller amplitudes. The pressure in the vessel attains a stable level, without any shocks. This level is characterized by the metastability or superheating of the liquid, i.e. the difference between the liquid temperature and the saturation point. It is demonstrated that the resultant pressure in the vessel is independent of the number of initial boiling centers or the initial pressure in the vessel and is determined only by the initial temperature. For water, the dependence of the superheating of the liquid on the initial temperature is found and compared with experimental data.

The problem of thermal growth of a vapor bubble moving in a superheated liquid is solved for two models of the phase interface, namely: a “rigid” (no-slip condition) and a “pliable” (slip condition) spherical surface. The second self-similar solution of the problem of the motion of a vapor bubble with a pliable surface is found. On the basis of this solution, an approximate dependence of the nondimensional heat flux into the bubble on the Jacob and Peclet numbers is constructed. For two limiting cases, namely, for a bubble growing at rest and a moving bubble of constant radius, this dependence coincides with the known solutions. The calculation results are compared with the experimental data obtained for vapor bubbles rising in a superheated liquid.

The depressurization of a high-pressure vessel initially filled with water heated to below the saturation point is investigated. After depressurization, the pressure in the vessel drops and the boiling fluid flows out into the atmosphere. The experiments [1–3] showed that, when the first rarefaction wave passes through the fluid and the pressure falls below the saturation point, a two-phase mixture with a small steam volume fraction (below 20%) is formed in the vessel. Intense boiling starts only after the arrival of a rarefaction wave traveling at a speed ∼ 10 m/s called the "boiling shock" in [4]. To explain the specific features of this process we developed a mathematical model which takes the difference in the phase velocities into account. Although in bubbly flows this difference is only ∼ 1 m/s, it is enough to cause bubble fragmentation. The calculation showed that the fragmentation proceeds like a chain reaction, i. e. one fragmentation event creates the conditions for the succeeding events. The avalanche-like bubble number growth leads to sharp boiling intensification and the rapid transition of the non-equilibrium mixture to the equilibrium state. This process occurs in a narrow region, namely, in a slow boiling wave which, in the numerical calculations, looks like a shock. The model developed has made it possible to obtain numerical solutions which agree well with the experimental data, to study the wave structure, and to explain the wave mechanism.

The rate of evaporation of liquid oxygen depends upon the density distribution of gaseous oxygen in the vicinity of the phase interface. The paper represents theoretical and experimental study of the problem. An analytical self-similar solution is obtained for the system of unsteady one-dimensional equations describing the flow of heat conducting mixture of mutually diffusing gases above the thermally destructing surface. The rate of evaporation, concentration and temperature profiles for various times are determined theoretically and compared with the experimental data.

A comprehensive program has been developed for calculating the optical characteristics and chromaticity of multielement optical systems. An analysis is given of how the chromaticity of multilens telescopes for endoscopes depends on the optical characteristics of the glasses that are used and the design of the antireflection coating. It is established that the main reason that chromaticity appears in the telescopes is the selective absorption of glasses that are used. A stepwise technique has been developed for choosing the antireflection coating to correct the spectral characteristics of the transmittance of the telescopes in such a way as to minimize the chromaticity while maximizing the total transmittance. Using the results of the calculations under production conditions, colorless multilens telescopes containing thirty-eight and thirty antireflection-coated surfaces have been fabricated.

The rate of layer-by-layer combustion of a monolithic solid unitary fuel is relatively slow, and depending on the external conditions equals -lO-S-lO "~ m/seco The mechanism of [lame propagation from layer to layer is determined by heat conduction in the condensed phase. In porous fuels, in the presence of longitudinal cracks and channels with small diameter, the velocity of propagation of the flame for separate compositions equals -10=-10 3 m/sec. In this case, the mechanism of flame propagation is qualitatively different: inflammation of subsequent layers is determined by convecti~a heat transfer as a result of leakage of hot reaction products into the channel. Depending on the composition of the fuel and the dimensions of the channel different mechanisms of propagation of convective combustion are possible. For relatively low rates of leakage into the channel the walls ignite as a result of direct contact with the hot reaction products; for high rates of leakage into the channel a shockwave (SW) forms, whose intensity is high enough for the flow of shock compressed gas to ignite directly the surface of the channel.