Low-rank hard coal was studied in order to characterize its propensity to formation of fine particles under vertically applied loading at micro- and nanoscales. To this end, micro- and nanoindentation tests were used. The vitrinite microcomponents of the selected coal were investigated due to their variations in mechanical properties with coal rank and type. Values of elastic moduli measured at micro- and nanoscales were similar. On the other hand, the scaling effects were observed during measuring of low-rank hard coal micro- and nanohardness, namely, the hardness linear decrease with growth of applied force. The effect of ‘strain hardening’ was found during repeatable (cyclic) nanoindentation with the increasing of the maximal load applied to the same area at the coal surface. This effect consists of rapid growth of hardness and elastic moduli values during repeatable indentation along with the increase of the applied maximal force. In the view of the previous investigations on mechanical behavior of brittle materials such as ceramics, and with the observations on coals crushing during nanoindentation, it was concluded that the aforementioned effects (scaling and ‘strain hardening’) are connected with the propensity of loss of the vitrinite structure integrity under vertically applied loads (at micro- and nanoscales).

Authors thank the Russian Science Foundation (grant #18-77-10052) for financial support of this work.


Сoal, mechanical properties, microhardness, nanohardness, elastic modulus, scaling effect, crushing.

Issue number: 2
Year: 2019
ISBN: 531+620.17
DOI: 10.25018/0236-1493-2019-02-0-69-77
Authors: Epshtein S. A., Kossovich E. L., Minin M. G., Prosina V. A.

About authors: Epshtein S.A. (1), Doctor of Technical Sciences, Head of Laboratory, Senior Researcher, e-mail:, Kossovich E.L. (1), Candidate of Physical and Mathematical Sciences, Senior Researcher, e-mail:, Minin M.G., Junior Researcher, Institute of Physics and Technology, Ural Federal University, 620002, Ekaterinburg, Russia, Prosina V.A. (1), Student, Laboratory Assistant, 1) National University of Science and Technology «MISiS», 119049, Moscow, Russia.


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