Вестник Научно-исследовательского института железнодорожного транспорта (Dec 2019)
Dehesion-deformational nature of friction and wear-out
Abstract
Two friction theories are compared: generally recognized adhesion deformation theory and alternative dehision deformation theory, founded by Prandtl and Deryagin. Concepts and peculiarities of effect of adhesion and cohesion forces of interatomic attraction are clarified. The concept of dehesion forces of interatomic repulsion is instroduced; their features are specified. Dehision deformation theory basic provisions are as follows: Compression of solid bodies results in occurrence of the interatomic repulsion forces, which after reaching the unstable equilibrium point (bifurcation point) can be instantaneously replaced with the cohesion attraction forces. Inversion (replacement) of forces forming new compounds are rare during friction, as bifurcation pressure (processes splitting) in the most pairs of substance is higher than the plasticity limit. Friction forces of solid bodies result from engagement of irregularities of the atomic-molecular roughness at the spots of actual contact. The proportionality of friction force to the normal force (Coulomb’s law) is ensured by increase of the depth of engagement of the atomic roughness, and by increase of the area of spots of actual contact. Displacement results in the cut-out of the contact surface areas. The cut-out particles of wear and tear act as the solid bodies; the particles are pressed in solid conglomerates and scratch the surfaces. Dry friction force is determined by the contact pressure, by the interlayer fragments strength, and by the strength of their links between each other and with the friction surfaces. In case of liquid friction, molecules are moved in a barrier-free irregular field of cohesion forces, thereby determining absence of friction of rest and dependence of friction forces on the flow velocity (Newton’s law), in contrast to gas friction resulting from collision of the freely moving molecules (Maxwell’s law). Liquids, which do not include polarized molecules, are pressed out of the friction area and do not affect the friction force. If lubricant includes SAS, then the friction force can change from maximum solid to minimum liquid depending on viscosity, SAS content, pressure, contact area, and slide-to-roll ratio (Stribeck dependence).
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