Hrechanyi O. Improvement of models of elements of mechanical systems reliability at their complex damage on examples of rolled rolls resource and their drive

The dissertation is concentrated on the research of complex diagnostic indicators and the rules of their combination, under the conditions of action on a separate element of the mechanical system of the complex of damaging processes. In the dissertation work, new scientifically substantiated theoretical and experimental results were obtained, which in aggregate are important for solving the urgent problem of assessing the technical state of units suffering from a combination of damaging processes, which ultimately ensured an increase in the reliability of rolls and their drive elements. Scientific novelty of the results obtained: - for the first time, a new rule was obtained for combining individual reliability indicators into an indicator of the reliability of the entire system based on the resource safety index and based on the Lindley distribution. - for the first time, the process of gradual mixed destruction of rolls with the development of circular defects in them is considered. At the same time, for the first time, a sequence of changes in the tangential and normal stresses from the force parameters of rolling in the volume of the roll for one revolution was formed - the method of taking into account the nonstationarity of the load during crack growth by determining the equivalent stress was further developed. - for the first time, a model of fatigue mixed rupture was developed and experimentally confirmed, which follows from the rule for combining resource safety indices. The practical significance of the developed technique lies in the possibility of its use in diagnostics of the operational state of complex mechanical systems, which include the main technological units of sheet-rolling equipment. The resulting technique was introduced into practice when carrying out repairs in the hot rolling department of a thin sheet of PJSC «Zaporizhstal» (implementation act dated 09.16.2020) and in the educational process in the preparation of bachelors and masters in specialty 133 - Industrial engineering at the Zaporizhzhya National University (act of use dated 03.09.2020). A new rule was obtained for combining individual reliability indicators into an indicator of the reliability of the entire system based on the resource safety index and on the basis of the Lindley distribution. The process of gradual mixed destruction of rolls with the development of circular defects in them was considered. In this case, for the first time, a sequence of changes in the tangential and normal stresses from the force parameters of rolling in the volume of the roll for one revolution is formed. For the first time, attention is paid to the cyclic change in shear stresses from the rolling force relative to a circular defect, which leads to the appearance of a mode II fracture mechanism. A scenario has been developed for the loss of rolls operability associated with the alternation of the action of destruction mechanisms according to the formula II → II + III → II + III + I. The characteristics of resistance to fatigue fracture of roll steels for modes I and II have been obtained experimentally, and schematized kinetic diagrams of fatigue fracture have been developed for them. Diagnostic models for sliding liners of universal spindles of sheet rolling mill have been developed, based on experimental industrial research. Due to the continued operation of the liners at the stage of accelerated wear, it is possible to increase their overhaul period guaranteed by 20 hours.