Study of the delay time in stress relaxation by the structure of a lubricating film on a friction surface with fullerene compositions

Abstract

The paper presents theoretical studies of the change in the delay time in stress relaxation in the structure of the lubricating film on the friction surface with fullerene compositions in the lubricant. The study of the structural viscosity of various fluids using rheological equations allows us to conclude that it is necessary to use such an indicator as the lag time.
The dependences of the change in the values of the delay time in the relaxation of stresses in the structure of the lubricating film on the friction surface were obtained theoretically, which make it possible to assert that the physical quantity Тlag takes into account the inertial properties of the structure. Small values of the delay time characterize the absence of delays in the relaxation of stresses in the structure of the material and residual deformations. Large values of the lag time characterize the presence of delays and the presence of permanent deformations in the material after stress relief.
It is shown that the value of the delay time complements the physical value of the relaxation time. The difference between the indicated physical quantities is in the confirmation of permanent deformations in the structures under study. The physical value of the delay time can explain the presence or absence of an oscillatory process of changing the friction coefficient, or a mode that called stick-slip. A decrease in the delay time in stress relaxation with increasing load indicates that the gel structure acquires elastic properties.
It has been proven that factors such as sliding speed, load on the tribosystem and tribological properties of the base lubricating medium have a significant effect on the lag time parameter, in the direction of increasing or decreasing. Conversely, factors such as the structure of compatible materials in the tribosystem, the magnitude of the friction areas and the concentration of fullerenes in the base lubricant do not significantly affect the value of the deformation lag time in the gel structure.