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hidden periodicities of the first and second orders and to determine their base

frequencies. The Fourier coefficients of mean and variation functions, as well as their

amplitude spectra, were calculated from the estimates of the fundamental frequencies.

Graphs of time dependences of deterministic oscillations and powers of stochastic

components are also presented. An analysis of the dependence of the correlation

components on the time lag was carried out, which reflects the properties of the high-

frequency modulation of the rotating harmonics of the disc. It was established that the

essential difference between dry and liquid friction vibrations is the frequency range

of vibrations, which, in turn, causes differences in the correlation of harmonics. Such

correlations are the result of spectral transition, which is occurring during high-

frequency modulation. The appearance of high-frequency vibrations during dry

friction in the second stage of the experiment is due to the nucleation of local damage

to the surfaces, which are already well developed in the third stage. The status

indicator value for this stage is greater than twenty. At the same time, for friction

with lubricated surfaces, the value of the condition indicator at the third stage is less

than seven, which corresponds to the beginning of the interval that determines the

average level of damage. Thus, a change in the interaction conditions of the contact

pairs significantly changes the vibration structure and affects the tribological

characteristics of the friction pair.

The main results of the work are formulated in the conclusions.

Keywords: periodically non-stationary random process, vibration signal,

stochastic modulation, friction, state indicator.