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

Fig.5.10. Scheme of change of the coefficient of friction f from the speed V of the relative displacement of solid bodies.
The stationary section takes place in the range of speeds V' _cr and V'' _cr , i.e. V' _kr ≤ 0 ≤ V'' _kr , I-kind seizing takes place at φ < V < V' _kr , II-kind seizing occurs at V > V'' _kr .
Seizure of the first kind occurs during sliding friction with low relative displacement velocities and specific loads exceeding the yield strength in the actual contact areas in the absence of a lubricant layer or secondary structures separating the friction surfaces. Seizure of the second kind is also a process of unacceptable damage to friction surfaces, expressed in the formation of local centers of seizure, welding, and this process is due to softening, deformation and contact of the juvenile surfaces of rubbing bodies. This process occurs during sliding friction with high speeds and specific loads. Significant heat release can lead to a significant softening of the surfaces and even to their melting, so that a layer of molten metal can form between the rubbing bodies, as a result of which friction even decreases (the area to the right of section III in Fig. 5.10). In the stationary section, the friction force practically does not change with time; in sections I and III, the friction force changes abruptly with time.
Dependence f = φ(V) can shift up or down when the process conditions change, and the stationary section can expand or narrow, which is determined by the conditions for the formation of secondary structures that ensure the existence of the stationary section.
One of the factors most strongly affecting friction is the frictional interface temperature , both generated during friction and obtained from an external heat source. As the temperature rises, the values of HB, τ ₀ , p _{r decrease} , and the penetration depth h increases. As a rule, with an increase in the bulk temperature T, _{the volumetric} adhesive component of friction f _adg decreases, and the deformation component f _def increases. In the general case, as the bulk temperature increases, the friction coefficient passes through a minimum (Fig. 5.11).