Journal of Friction and Wear最新文献

The results of experimental studies of solid lubricating coatings for space applications, in particular, one of the most effective coatings EONIT-3, are presented. The coefficients of friction of coatings and wear resistance at temperatures from minus 150 to plus 400°C in air and in vacuum 10^–6 mm Hg were studied for various combinations of antifriction materials depending on the contact pressure, sliding speed, indenter—disk and shaft—sleeve test patterns. It is shown that in tribochemical process molybdenum disulfide, the main industrial solid lubricant, plays the role of an active catalyst. Optimal and stable antifriction and physico-mechanical properties of the EONIT-3 coatings are observed after two hours of heat treatment at 200°C.

The work of tillage machinery is accompanied by a natural process of abrasive wear of soil-cutting parts, which leads to a decrease in the quality of technological operations and requires consideration in the development of new designs of such parts. The application of the method of paired modeling of the tribological process of abrasive wear makes it possible to obtain the necessary data for choosing the forms of hardening of the friction surfaces of soil-cutting parts, providing them with the required working life. The pair model proposed here is based on a combination of the results of simulation modeling on bench equipment and the values of the measured pressures in real soils in the zones of subsequent operation. Simulation modeling was carried out on a soil background corresponding to medium loamy soils, and during loading, the values of normal pressures were measured at different points of the friction surfaces and geometric shapes of normal pressure plots were built on the entire friction surface of the part. The measurement of the pressures of real soils was carried out by dynamometry of soil-cutting parts on soils intended for operation with the determination of power equivalents of total loading cutting parts on soils intended for operation with determination of power equivalents of total loading. In the paired model, a combination of simulation data and force equivalents of loading obtained under dynamometry conditions is performed, which allows us to have reliable values for the exact selection of materials and geometric shapes of soil-cutting parts focused on the guaranteed service life.

The structure and properties of powder steel–copper alloy antifriction pseudo-alloys infiltrated with materials of various compositions are studied, it is shown that mechanical and tribological properties are determined both by the composition and structure of the steel skeleton and, to a large extent, by the composition and structure of the infiltrate. It has been established that the limiting content of lead in the infiltrate, which ensures the absence of lead deposits on the sample surface and a large (10–15%) residual porosity, should not exceed 3%. The use of a mixture of copper powders and alloying additives for infiltration is more technologically advanced than atomized bronze powders. It is shown that the wear resistance of pseudo-alloys with a chromium steel skeleton depends to a lesser extent on the composition of the infiltrate, since the main contribution to wear resistance is made by a hard steel skeleton. The introduction of 3–5% ultrafine aluminum oxide powders into the infiltrate leads to an increase in the seizure pressure by 1.2 MPa and wear resistance by 20–30% due to the refinement of the copper alloy structure and the deceleration of dislocations that arise during deformation due to friction. It is shown that during the wear of pseudo-alloys in the surface layer the structure is refined, martensite is formed in the skeleton, and, accordingly, the microhardness increases by 720–760 MPa.

The following carbon nanostructures (CNSs) are used: shungite nanocarbon (Sh), multilayered graphene oxide (GO), multiwalled carbon nanotubes (Taunit-M), and fullerene C60. Medical Vaseline (MV) free from any additives or thickeners is used as a lubricant base. Tribological tests are carried out using a 2070 SMT-1 friction machine at a load of 2000 N. The roughness parameters of steel rollers before and after the tests are studied by profilometry. Detailed characteristics of contacting surfaces before and after friction are obtained by scanning and transmission electron microscopy. The experimental data are analyzed using the Hertz and Johnson–Kendall–Roberts models. According to the data on efficiency coefficients k_ef, the studied dispersions are ranked as follows in the order of deterioration of antiwear properties: MV/GO (0.5 wt %), k_ef of 50% > MV/Taunit-M (1.5 wt %), k_ef of 40% > MV/C60 (0.5 wt %), k_ef of 15% > MV/Sh (0.5 wt %), k_ef of 5%, which is in agreement with the above-mentioned sequence of CNSs at low loads. The reason for the best and worst wear factors upon using CNSs in the dispersions under study and factors affecting the values of wear in the hard friction mode are considered. The results of the study can be a basis for the development of new plastic lubricating compositions with carbon nanostructure additives for use in heavily loaded friction units.

Analytical and numerical modeling approaches for the contact-working system of turbo- and electric machines have been developed. The simulation allows determining some dynamic characteristics and loads in the rotor–stator system when there is a loss in clearance between them and there occurs subsequent motions with impacts or without separation from each other. In the system, the rotor and stator are deformable, the stiffness of rubbing surfaces is variable, and the working clearance between them is extremely small (50–500 times less than the rotor radius at the contact point). It is shown that the effect of the absolute elasticity for stator generates a significant change in natural oscillations of the coupled rotor–stator system, that is, a significant change in its eigenfrequencies and eigenmodes. It is noted that the elastic deformation of rubbing surfaces leads to a nonlinear increase in their contact stiffness, which consists of quasi-static and dynamic components. The consequences of an extremely small clearance are an elastic deformation of the contact surfaces commensurate with it (up to half the clearance size at the point of contact) during whirling with slipping of rotor over stator, as well as the disappearance of pure rolling, which is accompanied by the actual absence of rotary speeds even at low frequencies of contact whirling. The resulting diagrams of changes in the contact stiffness and whirling frequencies and the XY trajectories can serve as sources of initial information for identifying the operation of a real rotary machine on the threshold of a dangerous whirling with slipping and whipping and for further studies of contact oscillations of rotors.

The total resource of the assembly unit, as well as the post-repair resource of the unit, depend on the specified resource for critical joints. The main problem of calculating the joint accuracy is to determine the margin of accuracy or the margin of material for wear since an increase in the estimated fit tolerance will lead to a decrease in durability, and its decrease will entail an increase in costs due to an increase in rejects or the need to introduce a technological operation. In this regard, a method for calculating the joint fit tolerance depending on the specified or design wear characteristics was developed based on the analysis of the parametric failure model. When modeling various wear rates, it is recommended to use the relative wear resistance of the joint in the obtained dependences only if the wear function is approximated in a linear form. An expression for calculating the relative wear resistance of a joint is obtained depending on the wear resistance of the surfaces of the parts that form it. Using the example of calculating the fit tolerance of a rolling bearing operating under hydrodynamic friction conditions, the resulting fits are analyzed at a certain resource of no-failure operation of the joint for cases of increasing the wear resistance of the joint by 10 and 20%. The scientific novelty of the research lies in obtaining a theoretical relation between the fit tolerance and the probabilistic characteristics of the wear process at a specified probability of failure-free operation. The practical significance of research is expressed in the possibility of calculating the accuracy parameters of a particular joint at a specified resource.