Problems of Tribology

Determination of Limiting Deformations at Testing Cylindrical Samples for Tension

I. Iu. Kyrytsya — 2024-03-19

This paper proposes a method for calculating limiting deformations under conditions of localized deformation during tensile testing. The method for calculating limiting deformations was used to construct plasticity diagrams under conditions of strain localization under uniaxial tension.

The plasticity diagram is one of the material functions that forms the technological map of the material. The plasticity diagram displays the properties of a material depending on the degree of deformation and the stress state scheme.

According to the studies carried out in this work, it was established that the critical increase in plasticity with increasing stress state indicator is explained by the influence of three factors: the strain gradient, the history of deformation and the third invariant of the stress tensor.

The obtained dependencies make it possible to construct plasticity diagrams for materials whose destruction is preceded by localized deformation in the form of a "neck".

This work establishes the quantitative influence of these three factors on the magnitude of the limiting deformations of a sample stretched to the point of failure.

Application plasticity diagrams constructed using the proposed methods for cold plastic deformation processes, depending on the type of deformation path and the features of metal rheology, clarifies the value of the used plasticity resource of the metal, which allows to reduce the number of defective products for processes whose modes are calculated according to limit deformations.

Modeling surface structure of tribotechnical materials

I. Drach — 2024-03-19

Modern tribology makes it possible to correctly calculate, diagnose, predict and select appropriate materials for friction pairs, to determine the optimal mode of operation of the tribo-joint. The main parameter for solving friction problems and other problems of tribology is the topography of the surface. The main purpose of the models in these tasks is to display the tribological properties of engineering surfaces. In the framework of the classical approach, the topography of the surface is studied on the basis of its images from the point of view of functional and statistical characteristics: the evaluation of the functional characteristics is based on the maximum roughness along the height and the average roughness along the center line, and the statistical characteristics are estimated using the power spectrum or the autocorrelation function. However, these characteristics are not only surface properties. They depend on the resolution of the device for measuring the surface geometry and the length of the scan. However, the degree of complexity of a surface shape can be represented by a parameter called the fractal dimension: a higher degree of complexity has a larger value of this parameter. Fractal dimensionality is a characteristic of surface relief and makes it possible to explain tribological phenomena without the influence of resolution. This article provides an overview of mathematical approaches to the description of the relief of engineering surfaces, in particular statistical, stochastic and topological modeling, their limitations, advantages and disadvantages. The implementation of the principles of the theory of fractal structures is discussed, which makes it possible to introduce the degree of imbalance of the tribological system into the analysis of structure formation in the surface and near-surface layers of materials and to describe the development of friction and wear processes. This is the basis for controlling the structure of the surface layers of materials with given properties. The concept of fractals, used for the quantitative description of the dissipative structure of the tribojunction zone, makes it possible to establish a connection between its fractal dimension and mechanical properties, as well as critical states of deformation of metals and alloys. The course of research and stages of fractal modeling, the classification of methods of fractal analysis of the structure of engineering contact surfaces are considered. A critical analysis of modern models based on the energy-spectral density function, which are quite similar to fractal models, is presented. Readers are expected to gain an overview of research developments in existing modeling methods and directions for future research in the field of tribology

Study of Wear Resistance of Cylindrical Parts by Electromechanical Surface Hardening

D.D. Marchenko — 2024-03-19

The work scientifically substantiates the use of an effective technology for increasing the wear resistance of cylindrical parts, using the example of protective sleeves of cantilever pumps, due to electromechanical surface hardening. A review of research was carried out and it was established that the achievement of the highest values of microhardness of the surface layer at a depth of up to 1.2 mm is possible during electromechanical processing of protective sleeves of cantilever pumps. The application of various modes and schemes of electromechanical surface hardening (EMSH) is accompanied by a change in structure and, as a result, an increase in the hardness of the surface layer of the bushings. The actual contact area of the tool roller with the processed surface and the depth of the temperature-deformation effect depend on the physical and mechanical properties of the materials and the pressing force. The formation of a temperature gradient in the hardened zone at a depth of up to 1.2 mm from the surface has been proven. Metallographic analysis of the surfaces of the sleeves treated by EMSH shows the formation of a white layer with reduced etchability and increased hardness in the hardening zones. The results of the X-ray structural analysis confirmed the formation of the martensite phase in the hardening zone. The microhardness of the hardened steel zone increased by 2.6...3.6 times compared to the initial values at a depth of up to 1 mm from the surface, depending on the materials. In the case of their overlap, the alternation of a fully hardened zone, a partially hardened zone, and a self-relief zone is observed. At the same time, the microhardness of steels along the surface depends on the hardening scheme.

Wear tests under friction conditions of parts of cantilever pumps paired with stuffing boxes showed that the wear resistance of protective sleeves after EMSH increased by 3.1 times for 45 steel, 1.9 times for U8 steel, 2.5 times for SHKH15 steel, for cast iron by 1.9 times compared to the initial values. The use of U8 steel samples after EMSH, instead of serial bushings made of steel 45, allows to increase the wear resistance of parts by 6.1 times, which allows us to recommend U8 steel for use in the manufacture of protective bushings for console pumps. On the basis of the research, recommendations are given for the application of EMSH for the formation of a surface layer with increased wear resistance of protective sleeves during their production and during repair of console pumps in workshops or service centers of agribusiness companies.

Experimental installation for wear tests of materials and coatings

M. Stechyshyn — 2024-03-19

On the basis of the analysis of existing tribological testing methodologies, which includes the selection of controlled wear parameters, the influence of the type of friction, contact geometry, surface roughness, the scheme of tribological research, the choice of a machine 2168UМТ for friction testing of materials is substantiated. The friction machine allows you to install three samples at the same time, change the pressure in the contact zone in a wide range, control the moment of friction, the rotation frequency of the counterbody, the number of revolutions (friction path), change the rotation frequency, respectively, the sliding speed, automatically limit the distance traveled and other functions. The method of wear is adopted according to the finger-ring scheme, linear wear is monitored using an indicator rack with a value of divisions of the measuring device of 0.001 mm. To fix the samples on the machine caliper, holders were designed and manufactured, which ensure the self-fixation of the sample on the counterbody - a spherical joint made of the rolling body of the bearing. due to the fact that the samples were pressed against the counterbody with a force corresponding to the nominal contact pressure, they were self-aligned. After the sample was self-assembled, the whole structure was fixed by tightening the nuts. The counterbody is made of a rolling bearing ring, the material is steel SHX15, the hardness of the base is HRC 61. Three devices are mounted on the caliper for permanent lubrication of the running track immediately before the approaching sample. Thus, at certain values of pressure and speed, the mode of marginal friction can be reached, which was marked by a low coefficient of friction.

Determination of the regularity of the rate of wear of the working hydraulic cylinder of the mechanism of the sealing plate of the garbage truck from the pressing force

O.V. Bereziuk — 2024-03-19

The article is dedicated to the study of the influence of the pressing force on the wear resistance of the working hydraulic cylinder of the mechanism of the sealing plate of the garbage truck. The usage of a mathematical dependencies and appropriate software programs for regression analysis made it possible to determine the exponential regularity of the change in the rate of wear of the working hydraulic cylinder of the mechanism of the sealing plate of the garbage truck depending on the pressing force. A graphical dependence of the change in the rate of wear of the working hydraulic cylinder of the mechanism of the compacting plate of the garbage truck on the pressing force was made up, which confirmed the sufficient convergence of the obtained regularity. Graph of the influence of pressing force on wear rate of working hydraulic cylinder of the mechanism of the compacting plate of the garbage truck demonstrates the expediency of its increase. It was established that for the garbage truck of Ukrainian production of serial model KO-436, the rate of wear of the working hydraulic cylinder of the mechanism of the sealing plate of the garbage truck according to the obtained regularity will be 0.257 μm/h. The expediency of conducting additional studies to determine further ways to increase the wear resistance of the working hydraulic cylinder of the sealing plate mechanism of the garbage truck has been established.

Optimization of technological parameters at discrete strengthening of steel cylindrical surfaces

O. Dykha — 2024-03-19

The technologies of continuous strengthening of technological surfaces have practically exhausted their capabilities, which calls for the creation of fundamentally new approaches. The application of the principles of discrete-oriented strengthening of tribosystems has wide prospects for improving existing methods of strengthening due to the selection of modes and control of the geometric structure of the surface layer. The essence of the discrete-oriented strengthening method is the application of combined electromechanical processing and electrocontact cementation of cylindrical surfaces. The purpose of the work is to determine the parameters of discrete processing of cylindrical steel parts that are optimal according to the surface hardness criterion. Using the Statistica program, a factorial experiment was implemented according to the Box-Behnken plan, and the results of dispersion and regression analysis of the influence of processing parameters on microhardness were obtained. It was established that the following optimal parameters of DOZ processing are necessary to achieve the maximum values of microhardness (5950 MPa): current strength-500A, force-350 N, contact time-0.3 s.

Systematic approach to the study of working surfaces wear of automotive and tractor equipment parts

M.I. Chernovol — 2024-03-19

The paper uses the principles of the system approach to establish the relationship between wear of individual surfaces on the example of a gear drive of the GP type pump. The hierarchical structure of the part is considered, its individual functional parts are classified as subsystems, and the working surfaces are classified as system elements. A systematic approach to the study of part wear condition included, in addition to identifying the relationships between the wear of individual elements of the part, the creation of a mathematical statistical model of the worn part as a whole, as a system. The main types of wear of the gear working surfaces were determined. The laws of wear distribution of gear working surfaces and their main numerical characteristics were found. The established relationship between the wear of individual gear elements has become the basis for the system quality of the technical system "gear drive of the GP pump" in relation to the wear of its elements. A mathematical statistical wear model was obtained in the form of linear regression equations system of gear elements wear dependence on their outer diameter wear. This makes it possible, using the principles of a systematic approach based on the data of a single defect – gear wear along the outer diameter, to create a complete statistical image of the worn part, i.e., to determine the wear of other elements of the drive gear. The results obtained allow us to reasonably approach the issue of choosing a method for restoring parts and forming routes for the technological process of restoring a part.

Tribotechnical coatings

A.O. Zemlyanoy — 2024-03-19

Wear and tear limits the possibilities and shortens the operational life of modern technical systems. Therefore, the importance and necessity of consideration of issues aimed at reducing frictional forces and increasing wear resistance cannot be doubted. The paper summarizes the theoretical and applied results of triboresistance studies of detonation coatings of the Nb-Zr-V-Si-C-MgC2 system under conditions of constant loading in the field of sliding velocities. It has been established that the ratio of the quality of the components that make up the surface modified structures changes. It is noted that at the initial test speeds the presence of lower metal carbides that are part of the coating dominates, with an increase in speed under the current load due to solid-phase and diffusion processes, higher ones are formed in the graphite matrix carbides with enhanced thermodynamic properties.

Substantiating the mechanisms of electronic and phonon friction in the conjugation of materials of samples (parts) by the methods of solid state physics

V.V. Aulin — 2024-03-19

The article elucidates the essence of the mechanisms of electronic and phonon friction in the coupling of samples (parts) using the methods of solid state physics.

It is shown that in the triboconjugation of samples made of metallic materials, the flow of fluctuation-electromagnetic and electron-phonon processes should be distinguished. Fluctuation-electromagnetic interactions have long-range effects, and electron-phonon interactions have short-range effects. Based on Lifshitz's fluctuation-electromagnetic theory, the force of friction in moving couplings of metal samples is substantiated, taking into account the frequency ratio in the atomic absorption spectrum and the plasma frequency. A formula for estimating the friction force was obtained, taking into account the dielectric function and the Clausius-Mossotti formula.

The electronic friction force was estimated using the "jelly" model and the generation of electron-hole pairs in the quantum perturbation theory of solid-state physics.

The mechanism of electronic friction was discovered based on the phenomenological theory of braking losses of slow ions in solids. The scheme of the model of the electronic friction mechanism is close to the Persson model, which connects the braking force with the electron scattering process. A refined formula for estimating the electronic friction force is proposed.

The strength of phonon friction is justified on the basis of structural effects that can be induced by the mechanism of breaking adhesive bonds, and perturbation theory. A formula was obtained for estimating the force of phonon friction, taking into account the frequency of phonons, the inverse decay time and the function of the two-dimensional Fourier image of the force of interaction between the atoms of the conjugated surface of the triboelement.

Cases of static and dynamic phonon friction are considered.

Electronic and phonon frictional forces are considered at the nanolevel. The Debye low-temperature approximation and refinement of the expressions for estimating the electronic and phonon friction forces are given, taking into account the type of interatomic potential

A comprehensive method of researching the tribological efficiency of couplings of parts of nodes, systems and aggregates of cars

V. Aulin — 2024-03-19

In this work, a universal tribometer is proposed to study the tribological efficiency of the couplings of samples and parts. The design of the tribometer made it possible to carry out experimental studies in a wide range of force parameters of the load with their smooth change. A set of characteristics and parameters determined on tribometers during the study of couplings of samples according to the "disk-finger" scheme is given: wear intensity, coefficient of friction, temperature in the contact zone, specific work of destruction, specific energy capacity according to the heat index, electrical criterion for evaluating the structural adaptability of tribo couplings. Modes of friction and wear were determined by the characteristics of changes in the contact electrical resistance parameters: run-in, normal friction and wear, volume destruction. The results of the research of tribological efficiency according to the specified characteristics and parameters are given. For a comparative effect, the samples were strengthened by a complex chemical-thermal method, serial technology and boronization . The results made it possible to identify the characteristic zones of run-in regimes, normal friction and wear, and volumetric destruction. They are confirmed by the received electron microfractographies.