Yu. Yu. Makhovskaya

Modeling of friction at different scale levels

We construct a model for studying the common influence of the imperfect elasticity of actual bodies, the microgeometry of their surfaces, and their adhesive interaction on the contact characteristics (the contact pressure distribution, the region of actual contact) and on the sliding friction force. The model is based on the solution of a plane contact problem of sliding of a rigid body with a regular relief on the boundary of a viscoelastic foundation with surface molecular attraction in the gap between the surfaces taken into account. We analyze the influence of the surface microgeometry parameters at different scale levels on the character of the surface interaction (the saturated or discrete contact) and the friction force for different sliding velocities of the contacting bodies.

Effect of aluminum-alloy composition on self-lubrication of frictional surfaces

The influence of the mechanical and geometric characteristics of the hard and soft phases of an anti-friction alloy (yield limits of these phases, size and concentration of inclusions) on the amount of the solid lubricant appearing on the frictional surface is analyzed. The results obtained are used both to describe the existing anti-friction aluminum alloys and to give the recommendations for creating new wear- and score-resistant alloys.

The combined effect of capillarity and elasticity in contact interaction

The interaction between an axisymmetric punch and an elastic base with a meniscus of fluid between them is theoretically investigated. The shape of the punch is described by a power function. Both the case of contact of the bodies and the case where the bodies are separated by the meniscus are considered. The models of an elastic half-space and the Winkler foundation are used to describe the elastic properties of the base. The results are used to analyze the effect of elasticity of the interacting bodies on the capillary adhesion forces.

Experimental and theoretical evaluation of the deformation component of the coefficient of friction

An analytical model for the calculation of the deformation component of a friction force in sliding of a hard spherical indenter on a viscoelastic material that is modeled as a Kelvin solid is constructed. The influence of mechanical properties of a material and slip velocity of an indenter on the contact characteristics and deformation component of the coefficient of friction is studied. An experimental method for estimation of deformation loss under friction of a high-elasticity material is proposed. A comparison of the results obtained with the use of theoretical model with experimental data is performed.

Sliding of a wavy indentor on a viscoelastic layer surface in the case of adhesion

The contact problem of constant velocity sliding of the doubly periodic wavy surface of a rigid indentor along a viscoelastic layer on a rigid foundation is considered with the adhesive attraction between the surfaces taken into account. A method is proposed for calculating the configuration of the contact regions and adhesive interaction regions, the pressure distribution on the contact surface, and the deformation component of the friction force for various values of the viscosity, adhesion, velocity, and microgeometry parameters of the surface. We study how these parameters affect the merging of contact spots and the transition from discrete to saturated contact as the external load increases.

Modeling of soft phase transfer to the surface of multicomponent aluminum alloy in friction

A model for calculating the dependence of the amount of solid lubricant formed on the surface of a multicomponent aluminum alloy in friction is proposed. The constructed model is applied to analyze how the properties of the matrix and soft structural components as well as the alloy structure influence the amount of the soft phase transferred to the friction zone which provides for self-lubrication. Recommendations are given concerning the structural composition of the alloy (size and density of phase inclusions) in order to increase the thickness of formed lubricant film in specified friction modes.

Modeling frictional heating of fibrous composite brake disk

A model for calculating a nonstationary temperature field in a brake disk made of a fibrous composite material has been proposed. The calculation procedure includes solving the heat conductivity problem for a disk with averaged effective thermal conductivities and determining these effective coefficients with account for the structure of the composite at different scale levels, i.e., the structure of a bundle consisting of individual fibers at the microlevel, the dimensions and concentration of the bundles at the mesolevel, and the orientation of the bundles relative to the macroscopic shape of the disk. An example of the calculation of the temperature for a carbon–carbon composite brake disk under conditions of braking implemented in a friction machine is presented. An analysis of the effect of parameters that characterize the structure of the composite and properties of its components on the heating of the disk during braking is carried out.

Elastic contact between nominally plane surfaces in the presence of roughness and adhesion

The solution of the problem of interaction with regard to the forces of adhesive (molecular) attraction of two nominally plane half-spaces one of which is elastic and the surface of the other has a regular relief is presented. The surface mutual approach dependence on the applied nominal pressure and the effective specific work of adhesion are analyzed for various parameters of adhesive interaction and micro-geometry of the surfaces.

Modeling contact of indenter with elastic half-space with adhesive attraction assigned in arbitrary form

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.

Adhesive Component of Friction Between Rough Surfaces

Adhesion forces associated with molecular attraction have substantial influence on the characteristics of contact and the friction force between highly smooth and chemically pure surfaces. Bodies coated by surface liquid films can also experience significant adhesive attraction due to capillary pressure in liquid menisci formed in the gap between such surfaces.Copyright