Journal of Friction and Wear最新文献

To study the wear and friction force of a solid surface during friction with the ground, a carousel-type laboratory stand was created. The main task was to measure friction forces under various parameters of model soil and speeds of relative movement close to real ones during field agricultural work. Traditional electronic dynamometers are designed for static or slowly varying loads. Laboratory stands with such sensors have a linear design, a limited friction path (up to 2 m), and very low relative movement speeds (up to 0.15 m/s). The short friction path complicates the running-in process at the beginning of the experiment. Integral friction forces depend on speed. The adhesion component depends entirely on the presence of soil water at the interface and, thus, on the time required for water to move to the friction surface. With a carousel design of the stand, the friction path is infinite, and the speed can be increased by an order of magnitude (up to 1.5 m/s). Since studies usually compare the influence of different materials or soil compositions on the results of experiments, the systematic error due to the difference in the friction path from a straight line is insignificant. To measure rapidly changing loads, a force measuring station was developed based on a flat spring and a small displacement mechatronic sensor. The advantage of mechatronic linear displacement sensors is high sensitivity, ease of switching on, and high reliability. Disadvantages include dependence on temperature conditions and consequently the need for calibration in each experiment.

Friction is often accompanied by local fracture at the boundary of the contacting bodies. The gap between the bodies usually contains moving particles of different origin (“third body”), a change in the effective friction conditions may be associated with some changes in the structure of the third body. This paper presents a new series of experiments in which the process of rearrangement of intermediate layer particles interacting with various elastic materials (glass-rubber and steel) is modeled at different scale levels. A technique for visualizing the effect of mutual influence that occurs when two balls are pressed into a layer of rubber is proposed. It is the mutual influence that causes the effect of convergence or separation of the balls or particles during reciprocating frictional loading. The velocity of these processes depends on humidity and, in case of contact with the rubber layer, on the thickness of the layer. At high humidity, the configuration of the particles changes faster, and the friction force decreases. Replacing sand with an abrasive leads to an increase in the coefficient of friction and wear with a change in the microrelief of the surface. The minimum roughness is obtained for a humidity of 30%.

The work sets the task of determining the conditions for tribological testing of coatings in which the coating realizes its potential of physical, mechanical, and tribological properties regardless of the substrate. A standard method of tribological testing was used on a friction machine according to the pin–disk scheme with a circular motion of a spherical indenter pin. Experimental data are presented on the study of the structure and properties of vacuum ion-plasma nitride coatings of TiN, TiAlN, and CrAlSiN. The coatings had a thickness of 0.8–4.0 μm and were applied to plate steel samples intended for testing in a friction machine. The wear process of coatings is considered from the perspective of contact fracture mechanics and fatigue theories. A calculation and analytical model is proposed for quantitative assessment of contact and wear parameters during friction tests: the size of the contact area; the depth of contact approach; the depth of the plastic zone; stresses in the coating; fatigue limit; and critical thickness of the coating, which excludes its deflection. To assess the wear of coatings in this case, it is recommended to use fatigue failure models with the construction of a Woehler fatigue curve and determination of the fatigue limit based on the Murokami–Endo theory. The implementation of the recommended approach was carried out for the nitride coatings using a database of the authors’ experimental data.

The influence of the abrasive particle size and modifiers (low molecular weight liquid rubbers (LMWRs), sulfidosilane) on the rate of wear on abrasive paper of rubbers based on natural rubber (NR), carbon black (CB), and polyoxadiazole (POD) fiber is studied as a function of structure and mechanical properties of rubbers. Model rubber blends were prepared in a closed-type mixer, the abrasive wear tests were conducted on a drum-type machine, the structure and the mechanical properties of rubbers were characterized by DMA, static tensile tests, hardness measurements, and tear resistance. The wear surfaces were analyzed by SEM. Tests have shown that the addition of fiber does not affect the rate of abrasive wear of the original NR/CB rubber regardless of the grain size of the abrasive. Addition of modifiers that increase tensile modulus M10, hardness H_Sh, tear resistance T_R, tensile strength A, and degree of crosslinking γ reduces the wear rate under friction on coarse abrasive, which is characteristic of abrasive wear with a predominance of micro-cutting. The greatest influence, judging by the value of the correlation coefficient, is exerted by the value of M10, dependent on the bond strength between the matrix and the fiber, which allows predicting the wear rate of rubbers based on the results of mechanical tests. When worn on a fine abrasive paper, the increase in M10, H_Sh, T_R, and γ on the contrary, raises the wear rate of rubber, and the tensile toughness has practically no effect on it. This is attributed to the predominance of the fatigue wear mechanism, in which the wear rate increases with contact stresses, in proportion to the strength properties, with tear resistance exerting the greater effect on the wear rate.

The results of a study of the tribological properties and microstructure of rapidly solidified Al–12.2 wt % Si–0.2 wt % Fe (AK12vp) and Al–12.5 wt % Si–0.8 wt % Mg–0.4 wt % Mn–0.7 wt % Fe–0.9 wt % Ni—1.7 wt %, Cu (Al–Si–M) alloys are presented. The effect of multicomponent alloying on the microstructure of near-eutectic silumin was studied using scanning electron microscopy and X-ray spectrometry. Multicomponent alloying of the Al–Si eutectic alloy with magnesium, manganese, iron, nickel, and copper leads to a reduction in the size of the primary α-Al dendrites to 3–4 μm. Tribological tests carried out under conditions of dry friction with reciprocating motion of the indenter showed that alloying by metals of rapidly solidified eutectic silumin leads to a reduction in the coefficient of friction by 25%. An analysis of the surface state of the track showed that, as a result of deformation heating, the oxidation of the α-Al phase occurs, the destruction of the oxide film, which represents the third body, and its removal beyond the track. The fragmentation of silicon plates in the track area into nano-sized particles was also obtained. The impact of the indenter also leads to a uniform distribution of equiaxed particles of intermetallic compounds while maintaining their phase composition.

The contact problem of free rolling on a rigid foundation of a cylindrical body consisting of a non-deformable central part and an elastic rim is considered. A technique for an analytical solution is developed on the basis of a second-order asymptotic approximation. The contact interaction of the composite body with a non-deformable foundation under the action of a vertical force is investigated as a calculation example assuming a small rolling resistance moment. The calculated distributions of normal and tangential contact stresses, the distribution of the stress tensor intensity in the rim near the contact area, and the “force–displacement” dependence are obtained. These data are compared with the estimates obtained by the authors on the basis of finite element modeling and the results of using an alternative version of the asymptotic approximation. A conclusion is made about the advantages of the developed technique in comparison with the known asymptotic approach in terms of the accuracy of calculating the contact parameters and the simplicity of the applied mathematical apparatus. It is shown that the maximum of the stress tensor intensity is localized on the line of action of the vertical force (axis of symmetry) for a deformable rim material with Poisson’s ratio ν less than 0.4 and on the inner surface of the rim near the boundary of the adhesion and slip zones for ν > 0.4. The data derived are used to analyze the loading of roller interfaces of mining equipment.

One of the options for solving the scientific and applied problem of the predicted formation of ion-plasma coating tribological characteristics is presented. The problem is solved by creating and analyzing a carbon coating database. The object of research in this work is ion-plasma diamond-like coatings (DLCs) deposited on a steel substrate. It is shown that the use of nitrogen instead of hydrogen to stabilize carbon coatings not only ensures stable thicknesses of DLCs at the level of 1.0–1.5 μm, but also serves as an important and convenient technological parameter for regulating the tribological coating characteristics during deposition. Based on the predicted and experimental values of friction coefficient μ and data on sample path length L, the intervals of optimal values of technological parameters %N and λ are determined. The studied ion-plasma DLCs, obtained according to the established optimal application modes, can be recommended for application under friction conditions equivalent to the tribological tests carried out at friction load F ≈ 10 N.

Friction and wear of polyoxymethylene upon friction against polyoxymethylene and polyetheretherketone have been analyzed. It is shown that wear exponentially increases upon growth of contact pressure and sliding velocity in the homogeneous friction pair polyoxymethylene–polyoxymethylene. In the heterogeneous pair polyetheretherketone–polyoxymethylene the wear of POM is small and exhibits no registered dependence on sliding velocity and contact pressure. Mass-spectrometric analysis shows that the macromolecular decomposition products are not detected for polyetheretherketone–polyoxymethylene pair. However, for thermodynamically compatible polyoxymethylene–polyoxymethylene pair their formation, accompanied by the growth of friction force, is detected already at the levels of friction power as low as 10^–2 MPa m/s. These differences have been interpreted to result from interpenetration of polyoxymethylene macromolecules across the interface and their rupture in the shear field in homogeneous polyoxymethylene–polyoxymethylene friction pair and its absence in polyetheretherketone–polyoxymethylene pair. Thermally activated interpenetration of macromolecules for polyoxymethylene–polyoxymethylene pair and its absence in polyetheretherketone–polyoxymethylene pair has been visualized by means of molecular dynamics simulations. The experimental approach and the results of its application will be useful in detailed studies of molecular level friction mechanisms of friction and wear of industrially used polymers and their composites.

The study compared properties of carbon–carbon composites for manufacturing aircraft brakes. Composites based on various graphitized and carbonized fibers, coal, tar pitch, and pyrocarbon matrices were considered. Friction tests were carried out on full-size brake discs (three-disk stand) and on model samples (UTM-2168 testing machine). A significant wear increase of composites based on a pyrocarbon matrix was found during taxi braking in the temperature range of 50–250°C. Wear of composites based on a coal tar pitch matrix did not depend on the temperature of the friction surface. It was found, that the “third body” of composites based on pyrocarbon has a coarse rough structure with distinct individual abrasive particles; its hardness is more than twice as high as the hardness of the third body of composites based on pitch matrix. The size distribution of pores for composites based on different matrices is given, the difference in the quantity and size of structural defects is illustrated. The variation in wear of materials during taxi braking is explained. The increase of degree of anisotropy of the pitch matrix, provided the decrease of wear of the material. The wear was measured during taxi braking of specimens with a hybrid matrix having a different ratio of coal tar pitch and pyrocarbon components. Carbon–carbon composites containing 45% or more of the pitch component in matrix have stable reduced wear during taxi braking, regardless of the reinforcement scheme. The possibility of reducing wear during taxi braking of composites on pyrocompacted matrices by modifying the matrix with pitch is shown.

The paper considers wear-free friction of ShKh-15 (ShKh) steel balls on the surface of quartz glass (QG) and borosilicate glass (BG) vessels in organic liquids and water. It is shown that it is impossible to accurately predict which material will wear out faster: hard or soft, ball or substrate. The highest correlation between the wear of coupling friction surfaces is found for balls and the total wear of working bodies (r ≈ 1). In the group of glass balls, the balls wear out more often (19 out of 21 tests) than in the group of steel balls (5 out of 9 tests). Wearless friction is more often observed in coupled pairs BG/ShKh (5 cases) than in pairs QG/ShKh (1 case). Coupling surfaces containing only one terminal SiOH group do not provide wear-free boundary friction. The usefulness of the work is in the fact that the results of studies of wear-free friction obtained for the ShKh/H₂O pair can find practical application in the creation of bearings and large human joints.