Vol 37, No 4 (2016)

A model of the contact of an elastic indenter with an elastic half-space with adhesive attraction has been proposed. The adhesive attraction has been specified as an arbitrary dependence of the adhesive pressure that acts outside the contact zone on the gap between the indenter and the half-space. The shape of the indenter has been described by a power function with an arbitrary exponent. The constructed model has been used to study the applicability of a model with the single-step adhesive potential (the Maugis–Dugdale model). The results of calculations carried out using the Lennard-Jones potential have been compared to the results obtained using linear and exponential potentials.

This article describes the calculation-experimental approach to determining friction stresses based on an experimental dependence of friction force on the displacement of compressed surfaces. As an example of the approach application, analysis of Bowden’s mechanical model of friction is presented. In the approach implementation, we use the results of Courtney-Pratt experiment. Solutions are given in the power form.

The regularity of the self-setting of forces of friction during rolling has been established; i.e., an increase in the reduction ratio leads to an increase in the moment of forces, which hampers the rotation of a billet and is self-compensated with an increase in the moment of forces that favor the rotation of the billet due to the rise in the slippage of the billet against the tool. The linear dependence of Amonton’s coefficient of friction on the slippage of the billet against the tool has been obtained. The effect of the self-setting of forces of friction has been confirmed by the theoretical solution of a problem on the pressing of a ridge into a perfectly plastic solid, which is moved perpendicular to the direction of pressing.

The friction process is considered in this work from the viewpoint of chemical transformations, which occur in liquid lubricating medium and on the friction surface during the friction interactions. The results of tribotechnical tests of a conventional latten brass–glycerol–steel tribosystem are given and an attempt has been made to rationalize the evolution of tribotechnical characteristics of the tribosystem in the context of tribochemistry. The results of tunneling and IR spectroscopies indicate the formation of complex organic and organometallic films on the friction surface, which differ in chemical composition from the initial lubricating medium, which proves its deep triboconversion upon friction engagement. Chromato-massspectrometry studies of the products of tribotransformations of the lubricating medium enabled its identification. Based on this identification, chemical reactions, and a general scheme according to which tribochemical transformations take place in the lubricating medium have been suggested.

Unlike aliphatic polyamides, the friction coefficient of polyaramides depends not only on the relative concentration of hydrogen bonds in a macromolecule unit, but also on the structural factor, which is related to various positions of the hydrogen bonds in a phenylene nucleus, in this case, the para- and metapositions. During dry friction, aramide organoplastics are characterized by a high coefficient of friction, while for materials based on polyoxadiazole fibers, a low and stable coefficient of friction is retained.

The positive effect of the additional alloying of cast Fe–Cr–C steels on the formation of a secondary structure in the steels and their tribological characteristics under boundary friction has been shown. This effect leads to a decrease in the wear rate of the cast steel 1.2–5.2 times compared to that of the commercial 95Kh18 steel depending on the alloying system of the steels.

The results of investigations directed at improving the operational properties of composite materials of the diamond–(Fe–Cu–Ni–Sn) system have been presented. The computational procedure of optimal structural parameters of the diamond–metallic binder transient zone at which maximal mechanical and tribological properties of composites formed by sintering in hot molds with the subsequent additional hot pressing has been presented. Regularities of varying the structure of the transient zone diamond–metallic binder in compositions after sintering depending on parameters of hot pressing and their influence on mechanical and tribological properties of prepared composites have been revealed by X-ray structural analysis, scanning electron microscopy, and transmission electron microscopy. Ways of controlling structure formation processes for improving mechanical properties and wear resistance of composites have been shown.

This work represents the results of testing roller bearings for wear. In this study, we have measured vibration overloads and analyzed them with regard to the occurrence of damage in bearing parts. We have determined the relationship between the vibration intensity and the type of damage in working surfaces of roller bearing parts.

It has been suggested that the wear characteristics of a cultivator tip during tillage and a finite-element model based on the combination of the Euler and Lagrange methods be studied. The results of simulations show that surfaces with the largest contact loads correspond to the surfaces with greatest wear. It has been noted that the lower point of the front edge at a cultivator tip is under the action of the greatest contact load (120 N).