Dyrda V.I., Grebenyuk S.M., Sokol S.P., Slobodian S.B., Ahaltsov H.M. Some problems of investigation of nonlinear effects in elastomers with long cyclic destruction

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Parent Category: Geo-Technical Mechanics, 2019

Category: Geo-Technical Mechanics, 2019, Issue 144

Geoteh. meh. 2019, 144, 77-88

https://doi.org/10.15407/geotm2019.144.077

Some problems of investigation of nonlinear effects in elastomers with long cyclic destruction

¹Dyrda V.I., ²Grebenyuk S.M., ³Sokol S.P., ⁴Slobodian S.B., ¹Ahaltsov H.M.

¹Institute of Geotechnical Mechanics named by N. Poljakov NAS of Ukraine, ²Zaporizhzhya National University, ³Dnipro State Agrarian and Economic University, ⁴State Agrarian and Engineering University in Podilia

UDC 678:539.736

Language: Russian

Abstract.

In elastomers (rubber, polyurethane), there is a geometric non-linearity caused by the shape of the sample or asymmetric application of the load, and physical non-linearity caused mainly by the destruction and recombination of the filled structure. The latter form of nonlinearity is well known to technologists and is widely used in engineering practice: when filling rubber with technical carbon or other fillers (textile fibers, copper balls, etc.), the nonlinearity of its mechanical characteristics increases abruptly. Nonlinear effects in filled elastomers are expressed mainly in the dependence of shear modulus and energy dissipation coefficient on the amplitude of deformation. With very small deformations, rubber has a high rigidity, as deformation increases, its elasticity increases. This phenomenon is known as the Mullins effect and is explained by thixotropy, i.e. destruction and recombination of the filled structure. For weakly filled rubbers, thixotropy is practically not observed. Traditionally it is thought that such rubbers belong to the linear, and this linearity is maintained throughout the entire period of operation. That is, it is thought that in the linear rubber throughout the cyclic deformation until the failure of the samples, the linear dependence of the main informative parameters is preserved and the rubber completely obeys Hooke’s law.

At the same time, on the basis of numerous and long-term experimental studies of lightly-filled rubbers with their long-term cyclic loading, a regularity has been established, namely, that rubber with initially linear mechanical characteristics at a phase jump from the metastable to the labile state acquires significantly non-linear properties.

Such a regularity was confirmed experimentally in the study of the mechanism of cyclic destruction of lightly filled rubber: in the initial state in the range of relative shear deformations of 0-40 %, rubber obeyed Hooke’s law, i.e. possessed linear properties of the main informative parameters - shear modulus and energy dissipation coefficient. It is shown that in such a rubber, when moving from a metastable state (gradual-kinetic nature of destruction) to a labile one, initially linear mechanical characteristics become substantially non-linear.

The explanation for this is within the framework of the thermodynamics of irreversible processes. From a thermodynamic point of view, elastomers in the process of long-term cyclic loading are in a metastable state, i.e. in a strongly nonequilibrium state; for such systems, stability is provided by an increase in energy dissipation, which is observed experimentally. Moreover, the process of destruction of elastomers, as evolutionary in its essence, is characterized by the following: the presence of an autocatalytic mechanism for the growth of damage, which is the basis of the strong disequilibrium of the process of destruction and evolution of the material; lack of periodicity of the autocatalytic process, which ensures a unidirectional evolution of the material.

Keywords:

elastomer, amplitude effects, energy dissipation, shear modulus, phase transition, cyclic failure

References:

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About the authors:

Dyrda Vitalii Illarionovych, Doctor of Technical Sciences (D. Sc.), Professor, Head of Department of Elastomeric Component Mechanics in Mining Machines, Institute of Geotechnical Mechanics named by N. Poljakov NAS of Ukraine (IGTM NASU), Dnipro, Ukraine, This email address is being protected from spambots. You need JavaScript enabled to view it.

Grebenyuk Sergii Mykolayovych, Doctor of Technical Sciences (D. Sc.), Head of the Department of Mathematical Analysis in Zaporizhzhya National University (ZNU), Zaporizhzhya, Ukraine, This email address is being protected from spambots. You need JavaScript enabled to view it.

Sokol Sergii Petrovych, Candidate of Technical Sciences (Ph. D.), Senior Teacher of Dnipro State Agrarian and Economic University (DSAEU), Dnipro, Ukraine, This email address is being protected from spambots. You need JavaScript enabled to view it.

Slobodyan Sergii Borysovych, Candidate of Technical Sciences, Associate Professor of Department of General Technical Disciplines and Physics, State Agrarian and Engineering University in Podilia, Kamianets-Podilskyi, Ukraine, This email address is being protected from spambots. You need JavaScript enabled to view it.

Ahaltsov Hennadii Mykolaiovych, Master of Science, Junior Researcher of Department of Elastomeric Component Mechanics in Mining Machines, Institute of Geotechnical Mechanics named by N. Poljakov NAS of Ukraine (IGTM NASU), Dnipro, Ukraine, This email address is being protected from spambots. You need JavaScript enabled to view it.

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