Fig.5.4. Scheme and calculation of the deformation component of the friction coefficient.
and for the elastic contact of this conjugation according to the formula:
(5.7)
where α t is the hysteresis loss coefficient (α = 22α*, where α* is the hysteresis loss in uniaxial tension, and for metals α g * = 0.01 ... 0.14; for plastics and rubbers α g * = 0, 09...0.35).
The adhesive component of the friction coefficient obeys the binomial law:
(5.8)
where τ 0 - specific shear strength of molecular bonds at zero actual pressure; β is the coefficient of strengthening of adhesive bonds under the influence of normal compressive stresses; p r - actual contact pressure.
The binomial law of friction follows from the concept of the existence of a “third body”, which, during friction, is in a state of continuous form change, “flows” like a liquid in a narrow gap between two bodies moving one relative to the other. In this case, they proceed from the assumption that the resistance to shear of a single particle of the “third body” is proportional to the time of its settled life according to the Frenkel-Zhurkov equation (Fig. 5.5).
It should be borne in mind that in a slightly different form and from completely different ideas, the binomial law of friction was derived by B.V. Deryagin back in 1934.
Fig.5.5. Dependence of the adhesive component of the friction coefficient (specific shear resistance) and f adg on the actual pressure p r .
The values of τ 0 and β are determined experimentally.
The values of τ 0 and β for a number of common materials are tabulated (Table 1). This makes it possible to calculate the friction coefficients of these materials for different contact conditions and different microgeometry of the surfaces of the contacting bodies.
Table 1. Parameters of shear strength of molecular bonds during friction on hardened steel (according to I.V. Kragelsky and N.M. Mikhin)
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