Journal of Friction and Wear最新文献

This article presents the results of tests of the BrA5 bronze–45 steel reverse sliding friction pair in dispersion-lubricating media characterized by different degrees of surface activity with respect to bronze. Changes in the microstructural characteristics during metal tribodeformation are analyzed from the standpoint of the Rehbinder effect, which determines the possibility of selective transfer (wear-free mode) in tribological conjunction. It is shown that during friction of bronze in lubricating-dispersion media characterized by relatively low surface activity, the effect of the medium on the surface structure of the tribomaterial is based on the implementation of the surface-hardening effect, the total density of dislocations in the deformed near-surface layer increases. The wear intensity in this case is I_h ≈ 1.5 × 10^–7 to 4.0 × 10^–8. When bronze is subjected to friction in moderately surface-active media, both surface-plasticizing and surface-hardening effects are realized, with the latter predominating. In this case, the wear intensity decreases slightly, taking values in the range of I_h ≈ 1.2 × 10^–7 to 1.5 × 10^–8. During tribotesting of bronze in media with increased surface activity, the wear intensity of bronze remains at a fairly low level: I_h ≈ 2.2 × 10^–8 to 3.0 × 10^–8. However, in this case, two crystallographically isostructural solid solutions are formed in the near-surface layer of the tribomaterial, one of which is enriched with copper. Based on the concepts of physicochemical mechanics of contact interaction, the systemic and structural foundations of the materials science approach are presented, which underlie the analysis of the tribological efficiency of liquids used as dispersion media for plastic lubricants.

The evaluation of the determination of the friction coefficients and the wear intensity of an anti-friction material based on silver with the addition of molybdenum disulfide is given. The results of studies of the friction coefficients in the contacting pair are presented: SHX-15 steel and antifriction material based on silver with the addition of molybdenum disulfide. The average value of the coefficient of friction at a run of 1200 m, in a pair, a ball made of SHX-15 steel and a ring with a cover made of an antifriction material containing 94% silver and 6% molybdenum disulfide is 0.128 with a standard deviation of 0.006. At a run of 15 000 m, the average coefficient of friction was 0.129 with a standard deviation of 0.01. For a friction pair of an anti-friction material containing 94% silver and 6% molybdenum disulfide and SHX-15 steel, the coefficient of wear intensity of the antifriction surface at a contact voltage of 330 MPa is I = 0.86 × 10^–6 mm³/m, and for a counterbody in the form of a steel ball, I_b = 2.85 × 10^–8 mm³/m. Since the wear rate of the ball is two orders of magnitude lower than the wear rate of the friction material, the wear of the ball can be ignored in resource calculations. The obtained dependence of the coefficient of wear intensity on the maximum contact stresses will allow us to develop a calculation method for wear spherical articulated bearings.

The influence of the elastic-plastic properties of the coating-substrate system on the mechanical and tribological properties of coatings is investigated in the present work. The mechanical and tribological properties of the coatings were obtained by tribological testing and indentation. A screening experiment for vacuum ion plasma coatings of nitride systems of TiAlN and CrAlSiN deposited on steel substrates (38X2MYA, 12X2H4A) was performed. The mechanical properties of the coatings were determined using the NanoTest 600 continuous indentation method. The microstructure of the coatings and their surface topography were studied using a high-resolution ZEISS CrossBeam 340 scanning electron microscope (SEM). Tribological tests of the nitride coatings were performed on a TRB friction machine (Anton Paar Tritec) according to the methods of DIN 50 324 and ASTM G99. In addition, the indentation process of nitride coatings was studied based on the solution of the quasi-static contact problem when introducing a rigid indenter into an elastoplastic two-layer half-space. The mechanical characteristics H/E and H³/E² of the considered coatings and the conditions of adhesion failure between the layers have been determined. Theoretical studies are compared with the results of laboratory experiments. It is shown that when setting up laboratory experiments on indentation and tribological tests of coatings it is necessary to control not only the permissible depth of penetration of the indenter, but also the ratios of elastic-plastic properties of the coating and the substrate. It has been found that the service life of tribo-conjugate elements with coatings of a certain thickness can be increased by combining the elastic-plastic properties of the layered medium adapted to the given loading modes. This will prevent the localization of tensile and compressive stresses and delamination and cracking at the interface of two materials.

The dynamic response of a layered medium (using road pavement as an example) to a dynamic impact for the conditions of cohesive contact between individual layers and complete slippage is analyzed. To solve this problem, a mathematical model of the dynamic stress-strain state of a layered half-space is used, based on solving the Lamé equation in displacements, using the Hankel integral transform, amplitude–frequency characteristic (AFC) of accelerations on the medium surface under study, obtained directly from the displacement AFCs. In the course of a numerical experiment on this model, it is found that the case of adhesive contact between the layers of the road pavement corresponds to the presence of one clearly expressed frequency extremum on the acceleration AFC. The case of “complete slippage” corresponds to the presence of a number of frequency extrema on the acceleration AFC. In this case, when modeling the full slip at the boundary of the half-space lower layer and the underlying half-space and varying the elastic modulus of the half-space, the presence of a clearly defined frequency extremum in the range of 426–531 Hz is noted, presumably corresponding to oscillations of the underlying half-space itself. The established patterns can be used to improve the methods and means of non-destructive testing of layered media, in particular to increase the information content of their structural state, which is necessary for making decisions on repair or overhaul.

An analytical method of calculating contact parameters during rolling of a cylindrical body, having a thin viscoelastic surface layer, over a rigid sideway was developed. The technique is based on elastic-viscoelastic analogy and asymptotic approximation of the exact solution of the elasticity theory problem for a thin strip. The mode of steady rolling at given normal force and speed of motion of the center of the rolling body is considered. In the example of calculation the initial parameters corresponded to rolling support of a mine skip with rolling elements in form of steel rollers with a polyurethane rim. The dependences of rolling resistance force (which is parallel to the supporting surface) on speed, friction coefficient during sliding, and Poisson’s ratio of the rim material were obtained. The dependence of rolling resistance force on speed has a maximum, which corresponds to a speed of 8 m/s in the example considered. The rolling resistance decreases as Poisson’s ratio of the rim material increases. The calculated values are compared with assessments of contact parameters obtained within the framework of a simplified Winkler’s base model. It is shown that the discrepancy of results does not exceed 5%. The developed technique can be used for designing and predicting the durability of metal-polymer rolling bearings.

Based on the mechanics of discrete contact of rough surfaces of machine parts, quantitative criteria are proposed that determine the boundaries of fretting wear regimes. The physical foundation of these criteria is the ratio of the amplitude of tangential oscillatory displacements of contacting bodies and characteristic linear quantities associated with the dimensions of the real contact areas of the contacting surfaces. It is convenient to characterize fretting wear regimes using maps on which the boundaries of the areas of the corresponding regimes are shown in the coordinates: oscillation amplitude/normal contact load (or nominal contact pressure). The influence of the wear regime on the life of one of the common types of connections subject to fretting wear, namely electrical contacts, has been shown experimentally. Using a map of fretting wear regimes, the influence of the amplitude of tangential oscillations and normal load on the dependence of the contact electrical resistance on the number of oscillation cycles under different regimes was analyzed. The fundamental difference between this dependence in the fretting wear regime and in the normal reciprocating sliding of contacting surfaces is shown. The proposed criteria of fretting wear regimes and their visual representation in the form of wear regime maps allow predicting the wear mechanism of a given contact joint. Understanding the wear mechanism allows for a reasonable choice of materials for contacting parts and contact joint parameters (contact pressure, contact rigidity) to ensure the reliability of friction joints, including electrical contacts, under fretting wear conditions.

Compositions of ashless thiophosphoric and thiocarbamine compounds were studied as a tribologically active additive. Studies of the anti-wear properties of compositions in both fresh and oxidized oil samples in comparison with the effectiveness of a similar functional effect of a traditional additive, zinc dialkyldithiophosphate, were carried out on a tribometer that implements the wear process of conjugated pairs under sliding friction conditions simulating the boundary lubrication mode. The results of tribotests of mixtures of these compositions with metal-containing detergents of various chemical nature in a solution of synthetic lubricating oil as model variants of the composition of engine oils are presented. The synergism of the action of the ammonium salt composition of dialkyldithiophosphoric acid and methylene bis-dibutyldithio-carbamate, which provides a reduced content of sulfate ash and phosphorus, factors of environmental safety of the use of oils, is noted.

A study was carried out on the influence of the cooling rate of gas-thermal coatings made of high-chromium 95Cr18 steel on their phase composition and tribotechnical properties. It has been established that preheating the steel substrate to 400°C before spraying the coating leads to a 2.7-fold decrease in its cooling rate in the region of bainite transformation and an increase in the content of retained austenite in the coating to 83.5 vol %. It is shown that the stabilization of austenite is due to the redistribution of carbon between the α- and γ-phases and the enrichment of austenite with carbon. It has been established that a coating made of 95Cr18 steel, sprayed onto a substrate heated to 400°C, is characterized by higher wear resistance under various friction conditions (by 12–24%) compared to a coating formed on a cold substrate. High wear resistance of coatings with a high content of the γ-phase is achieved due to the deformation-activated γ → α transformation, leading to a significant increase in microhardness and wear resistance of the surface layers of coatings.

The dependence of gear tooth wear on the angle of skew is investigated. It is noted that in gear mechanisms, due to elastic deformations of the elements, manufacturing and installation errors, the symmetry of the system’s compliance is violated, and instead of nominal contact between the teeth, edge contact takes place. As a result, there is a concentration of stresses in the places of initial contact of the teeth, contact stresses sharply increase in these places, which in turn cause increased wear of the teeth in these zones. Because of this, the load capacity of the transmission is reduced, and the durability of the entire mechanism is also significantly reduced. From what has been said, it is important to establish the dependence of the wear value on the transmission load parameters, primarily on the angle of skew. The problem was solved using the method proposed in the paper using an elastic base model. In order to increase the accuracy of matching the specified model with the real picture, a bed with a variable base coefficient is used in the work. Formulas are obtained in closed form for the amount of wear as a function of the skew angle. Verification of these formulas according to the experimental data available in the literature has shown good convergence. It was found that the misalignment significantly increases tooth wear. The results can be useful in the design of gearboxes with cylindrical gears.

The article discusses the factors affecting the operation of sliding bearings. It is shown that based on the fundamental principles of hydrodynamic lubrication theory, transitioning from the formula characterizing the load-carrying capacity of the lubricant layer in sliding bearings to the parameters of oil film thickness and clearance allows for the derivation of expressions to determine functional clearances within which the bearing will operate under conditions of hydrodynamic friction. As a result of the calculations conducted for the sliding bearing of the conveyor drive reducer the limiting functional clearances were defined for the use of bushings of various lengths in accordance with GOST ISO 4379–2006. A rational length for the sliding bearing trunnion is justified based on the value of the maximum functional clearance and its influence on the deviation of the center distance in the gear transmission of the reducer. A new H8/f7 fit is proposed instead of the recommended H8/g7 and H8/e7 fits according to GOST ISO 4379–2006, as this will ensure the presence of a hydrodynamic wedge at the beginning of operation and provide the most rational material reserve for wear. The practical significance of the research lies in the applicability of the proposed approach in the design of sliding bearings operating under conditions of hydrodynamic lubrication, aimed at determining the rational length and fit of the mating elements in the bearing assembly.