Institute of Problems of Mechanical Engineering of the Russian Academy of Sciences (RAS) (Russia), REC «Mekhanobr-Tekhnika» (Russia):

Blekhman I. I., Doctor of Physics and Mathematics, Professor, Head of Laboratory, iliya.i.blekhman@gmail.com
Blekmman L. I., Ph. D. in Enginering Sciences, Leading Researcher, liblekhman@yandex.ru
Vasilkov V. B., Doctor of Enginering Sciences, Leading Researcher, vlvasilkov@yandex.ru

Wear of nominally fixed joints of machine parts, being in contact through dry friction and operating under conditions of impact loads, is considered. The machines in question are exemplified by screens, crushers, mills; while the joints in question are exemplified by flanged connections, bolt – nut connections, etc. This kind of wear is of paradoxical character: at first glance, it should not occur. The paper considers two directly contrary mechanical models of this kind of wear, that may be termed vibrationally-frictional: two-mass model and distributed parameter model. Normal force oscillations, caused by impact momenta, result in short-duration moderation of contact force that presses parts to each other, and microslip occurs. Exactly these phenomena are described by the proposed models. Microslip magnitude estimates, required for wear rate assessment, as well as the formulas, describing negative effective dry friction, were obtained. It is worthy of note that with respect to the both models, essentially different one from another, the respective estimates related to the made assumptions prove to be analogous. So, decrease of pressure at right angle between the parts in question in both cases is equal to product of impact momentum and natural frequency (for the second model — base frequency). It has been noted that the investigation results are applicable to the theory of man-induced seismic incidents. It was shown and verified by experiment that even a relatively slight impact action may cause body displacements, significantly decreasing negative effective dry static friction. So, drop of steel ball weighing 8 g from 20 cm height on steel plate weighing 2225 g decreases negative effective dry static friction almost by the factor of two.
The work was performed with the financial aid from the Ministry of Education and Science of the Russian Federation for the Project No. 14. 607.21.0120 UIPNI RFMEFI60715X0120.

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