Journal of Friction and Wear最新文献

Based on the proposed loading model of a sliding bearing, the dependence of the load-bearing capacity of reinforced metal fluoroplastic sliding bearings on their geometric characteristics and force factors was studied using the finite element method. A calculation of stresses and deformations in the most pliable antifriction layer was carried out. It is shown that the distribution of stresses and deformations in the bearing is extremely uniform and depends on the thickness of the antifriction layer and the height of the bearing. Criteria for assessing the performance of sliding bearings under load were introduced and based on these criteria the results were compared with experimental data. The agreement between calculated and experimental data allows us to use the resulting methodology to determine the load-bearing capacity of slide bearings. The solutions make it possible to move from the experimental method of determining the load-bearing capacity of metal fluoroplastic sliding bearings to the calculated one and to design bearings with predetermined strength characteristics. This will help specialists designing bearing units improve the quality and speed of their development.

It is shown that friction fracture surfaces can be self-affine with a local fractal dimension. However, the intersection of such a self-affine surface with a plane gives similar contour lines, which are undoubtedly self-similar. The above considerations regarding the fractal properties of fracture surfaces give reason to believe that a rough surface in contact with metallic bodies in the process of friction is also self-similar. This article presents the fractal dimensions of the transient contact regimes (from elastic to elastoplastic and from elastoplastic to plastic contact) for self-affinity curves, which are the curves of the reference surface at various combinations of material parameters: Poisson’s ratio, hardness, and modulus of elasticity. In the calculations, the Minkowski dimension, calculated by the cellular method, was taken as the fractal dimension of curved reference surfaces. This method, based on the consideration of contact interaction, formed the basis of the method for calculating the contact characteristics of bodies, taking into account their macroshape and the roughness of friction surfaces. The results of the study are of great importance for the development of engineering methods for calculating homogeneous and inhomogeneous rough bodies.

This paper presents the results of tests of EPAN coatings, a composite material based on carbon–carbon fibers. It uses fine molybdenum disulfide as the main lubricant and for binders, phenol, peroxide, and silicone resins. The tests were carried out on microarc oxidation (MAO) coatings. For comparison, the tribological characteristics of EPAN under friction on steels, as well as molybdenum disulfide composites are given. The friction coefficients of EPAN coatings on MAO coatings according to the “shaft–bushing” scheme do not exceed 0.05 at pressures of 10–20 kg/cm² and shaft rotation speeds from 130 to 600 rpm. The advantage of such combinations of materials is the use of a light alloy, aluminum with MAO coating, for the counterbody to the EPAN coatings, which is important for space products. The creation and testing of solid lubricating coatings for modern space technology is a task of extreme importance, because in many developments of space products, low-temperature plastic lubricants continue to be used, which are operable up to subzero temperatures of –90 to –110°C. Such solutions require the use of thermal insulation and heating for mobile interfaces and friction units of machines, mechanisms, and devices. The result is a serious complication of structures and an increase in their weight. The tests of EPAN coatings on MAO coatings carried out in the work open new possibilities in the combination of materials for space technology. Having a coefficient of friction of 0.05 and high wear resistance, they allow you to create movable joints, first of all, sliding bearings, for operation on Earth sensing satellites, as well as mechanisms on the Moon.

The evaluation of the corrosion wear rate was carried out using the Norsok Standart M-506 method for oilfield production tubing in Belarus. The method is based on a model that takes into account the speed of the gas-liquid flow, its pH, the volumetric flow rate of water, oil, gas, pressure, temperature, immersion depth, pH, density and viscosity of these media, and diameter and wall thickness of tubing. A feature of the model is the consideration of the friction of the gas-liquid flow on the walls of the tubing and the resulting shear stresses near them, which allows taking into account the corrosion-mechanical component of the metal degradation process of the tubing. The characteristics of well media and operating conditions of equipment in fields are given. Empirical coefficients of the considered model for typical conditions of Belarusian oil fields have been determined and a predictive calculation of the corrosion rate of 32Mn1A tube steel strength group N80 (Q) of the API Specification 5CT has been carried out. Data on actual values of corrosion wear of tubing from more than 100 production wells have been collected. The results indicate a high convergence of calculated and actual data. The adapted Norsok Standart M-506 method of predicting corrosion wear is recommended for use at oil fields in Belarus. It is shown how the proposed approach can be extended to other oil-bearing regions.

Within the framework of physicochemical mechanics (the Rehbinder effect), the problems of the plasticizing and strengthening effect of the lubricating medium on the near-surface layers of metal tribomaterials are analyzed. The influence of modeling (petroleum jelly oil, glycerin, mineral oils, glycerin-based hydraulic fluids) and industrial (Buksol, Puma, and M-14V2) lubricant media that contain surfactants, is investigated on the main tribological (coefficient of friction, wear intensity), strength (yield strength, microhardness) and microstructural (broadening of X-ray lines, dislocation density and crystal lattice parameter) characteristics, as well as on the processes of diffusion redistribution of alloying elements in surface layers of tribomaterials, such as copper, brass, and bronze, when they are rubbed together with steel. The analysis of the conditions of formation and stable functioning of the regime of “non-wear” friction in these tribomaterials is carried out. It is shown that among industrial copper alloys, brass of the L90 type, aluminum bronzes BrA5 and BrA7, and tin bronzes BrSnP4-0.25 and BrSnP6.5-0.15 have the greatest wear resistance in surface-active lubricants. Examples of the implementation of the selective transfer mode in tribo-pairs used in railway and motor transport are given.

The tribological properties of carbon–carbon antifriction composite materials reinforced with carbon fabric based on polyacrylonitrile and viscose raw materials have been studied. Tribological tests were carried out according to the ring–disc scheme paired with silicon carbide ceramics under dry friction conditions with different orientations of the composite fabric layers relative to the friction surface in the temperature range of 80–100°C. Dependences of the friction coefficient and wear rate on the fabric orientation relative to friction surface, structure of the composite, and properties of its structural components were obtained at a fixed load and sliding speed. The surface of composites was analyzed after tribological tests using scanning electron microscopy and optical profilometry. The composites friction and wear mechanisms for different contact configurations and different material properties have been revealed. The characteristic features of composite individual structural (fibers, fiber bundles, layers of reinforcing fabric) frictional destruction have been determined. It has been established that the film of wear products formed on the friction surface has a decisive influence on the tribological characteristics of the studied materials. Combinations of the fabric base of the composite, its orientation relative to the friction surface, and the heat treatment mode of the material were determined, which simultaneously provide increased wear resistance and reduced friction in tandem with a ceramic counterbody.

Samples of fasteners were studied: bolts, nuts, and washers with a zinc coating applied in various ways, namely galvanic, thermal diffusion, gas thermal, hot galvanization in molten zinc and in melt galfan (Zn + 5% Al), as well as with zinc lamellar coating. Data on roughness, microhardness, and friction coefficient of zinc coatings were obtained. It has been established that the thermal diffusion coating has the greatest hardness, and the coating obtained by hot-dip galvanizing in molten zinc has the least hardness. Maximum roughness R_a is observed in gas-thermal and thermal-diffusion coatings. The lowest roughness is found in coatings obtained by hot-dip galvanizing and galvanic deposition. The friction coefficients of coatings were studied in finger-disk geometry for all types of coatings. It has been established that zinc-lamella and thermal diffusion coatings have the highest coefficient of friction, and the lowest, gas-thermal coating and those obtained by hot-dip galvanizing. The nominal tightening torques for M3, M10, and M16 bolts are calculated. It has been established that the tightening torque of coatings applied by hot-dip galvanizing in molten zinc and gas-thermal spraying complies with the standards of RD 37.001.131–89. For other coatings, the friction coefficient requires adjustment through the use of lubricants or the application of additional coatings. The results can be used when choosing a zinc coating for fasteners.

Nanoindentation at temperatures of 23 and 150°C is used to study the coating of molybdenum disulfide doped with silver and calcium fluoride. The Nanoscan-4D scanning nanohardness tester was used for the experiments. A method is presented for determining the elastic properties of a coating from elastic indentation curves, taking into account the real shape of the indenter head, which is determined by optical profilometry. The elasticity modulus of the coating is determined based on the exact solution of the contact problem for a two-layered elastic foundation, taking into account the calculated compliance of the measurement system. Newton’s method is used for the inverse problem solution. The input parameters of the problem, in addition to the geometry of the indenter head and the load, are the elastic properties of the head and substrate materials. The elastic type of indentation was provided at maximal load of 10 mN for both temperatures. The loading–unloading curves at room temperature and at 150°C turned out to be close (within the experimental error), which proves the stability of the elastic properties in the considered temperature range. The calculated elastic modulus of the coating was 326 GPa. Using the same device, equipped with a lateral force sensor, the sliding friction coefficient of the coating was determined under different loads (5, 10, and 20 mN). Such a study can be considered as a physical model of the contact of the coating with a single asperity. The experiments were carried out on straight tracks 1 mm long at a speed of 11 µm/s. It is shown that the coatings are antifrictional (with friction coefficients in the range 0.033—0.078). The coefficient of friction increases with increasing load, which may be due to the dissipation of energy for plastic deformation of the coating material at relatively high loads. The conclusion about the presence of plastic deformation is based on the results of optical profilometry, which showed plastically deformed and pushed material along the edges of the friction track under relatively high loads. At low loads, this phenomenon is not observed. This coating can be used in sliding friction units that require one or two applications with a low friction coefficient.

The study of the structural-phase state and tribotechnical properties of antifriction gas-thermal coatings made of aluminum alloy AlSi12, welding bronze CuSi3Mn1, as well as composite material CuSi3Mn1 + AlSi12 and a coating of bronze CuSn10P1 obtained by centrifugal induction surfacing was carried out. It is shown that composite gas-thermal coatings from CuSi3Mn1 + AlSi12 after spraying include Cu, Al, Cu₉Al₄, CuAl₂, Cu₃Al, Si, and Al₂O₃ phases. The matrix phase of the bronze interlayers is doped with aluminum, while the Al interlayers are doped with copper. It has been established that annealing of coatings CuSi3Mn1 + AlSi12 at temperatures of 175 and 225°С for 2 h leads to the release of an additional amount of intermetallic compounds in them and an increase in their microhardness. It is shown that composite gas-thermal coatings have ≈1.2–1.7 times higher wear resistance in the environment of I-20A and Litol-24 lubricants compared to coatings of CuSn10P1 bronze. Annealing of composite coatings from CuSi3Mn1 + AlSi12 leads to an increase in their wear resistance in the environment of I-20A liquid lubricant up to 30% and Litol-24 up to 20% compared to the initial state. The coefficients of friction of all antifriction coatings based on copper in the environment of the I-20A lubricant did not exceed 0.08, and in the environment of the Litol-24 lubricant, 0.10.

The article presents the results of experimental studies on the effect of circulation pump operating modes on the wear of a double reciprocating slit throttling hydrostatic bearing operating in a lead coolant environment. The experiments were conducted on a high-temperature circulation test bench at a lead coolant temperature of 420–450°C. Results were obtained for operation modes with a high number of start-stop cycles (approximately 100 cycles per 100 h of operation), sustained operation with a low number of start–stop cycles and nominal speeds of 1000–1100 rpm (not exceeding 8 cycles per 100 h of operation), with 25 start–stop cycles per 100 h, and at low pump speeds below nominal values of 600–700 rpm with a maximum of 8 start–stop cycles per 100 h of operation. Data on the wear of the bearing bush and shaft are presented in the article. Processing and analysis of the research results led to the conclusion that this type of bearing can be used in low-pressure axial pump systems only under conditions where the pump creates a head exceeding 1.1 m of liquid lead.