O’zbekistоn respublikasi оliy va o’rta maxsus ta`lim vazirligi

Fig.5.3. Areas of localization of external and internal friction (according to Polzer and Meisner)
The process of external friction is influenced by a large number of factors. but ultimately the main role is played by the interaction of solids with each other in the areas of tribological contact. This interaction consists in overcoming the forces of molecular attraction (adhesion) between the contacting bodies on spots (elementary areas) of the actual contact area, as well as in the shape change of the relief of the contacting bodies as a result of their elastic and plastic deformations of their surface layers. Thus, friction is determined by the processes of deformation of surface layers and the adhesion of contacting bodies as a result of their intermolecular interaction.
According to the molecular mechanical theory of I.V. Kragelsky, the friction force can be considered as the sum of the adhesive and deformation components
F = F _adg + F _def , (5.4)
where F _adg and F _def - adhesive and deformation components of the friction force acting on elementary contact patches.
Friction coefficient calculation
The most common characteristic of the friction process is the value of the friction coefficient f, which is equal to the ratio of the friction force F of two bodies to the normal force N pressing these bodies to each other. In this case
(5.5)
those. the friction coefficient has two components - deformation and adhesion. Let us consider the calculation of the coefficient of friction of two bodies in relation to the contact of a single roughness with a deformable half-space and the coefficient of friction in multiple contact.
The calculation of the friction coefficient at the contact of a single unevenness is reduced to the determination of its deformation and adhesive components.
The deformation component for a single contact is determined by the relative penetration depth h/r, i.e. the ratio of the depth h of the introduction of a spherical roughness to the radius r of this roughness (Fig. 5.4). The value of the deformation component is calculated for the plastic contact of a single roughness with a deformable body according to the formula:
(5.6)