Mechanical properties instructural planes of tectonic coal and primary coal through nano-indentation
Coal and gas outbursts,alongside other dynamic hazards within mines,are known to pose a severe threat to both mine safety and the efficiency of production.Consequently,the re-search into the micro-scale strength,deformation,and rheological properties of various coal types takes on substantial importance in the context of enhancing mine production efficiency and averting potential disasters.In this study,nano-indentation technology was employed to conduct tests on the structural planes of typical tectonic coal and primary coal specimens,with a focus on investigating the micro-scale strength,deformation,rate sensitivity,and creep characteristics of these coal varieties.The results show that,under equivalent loading condi-tions,tectonic coal exhibits greater deformability compared to primary coal,accompanied by weaker elastic recovery.The deformation dissipation energy in tectonic coal is approximately double that observed in primary coal,and certain structural similarities between the two are evident.As the loading and unloading rates are reduced,there is an associated increase in the proportion of elastic energy,while dissipation energy,elastic modulus,and stiffness decrease.It is noteworthy that when the loading and unloading rates fall below 100 μN/s,significant fluctuations are observed in the strength characteristics.Conversely,for loading and unloading rates exceeding 100 μN/s,strength characteristics display reduced fluctuations with varying rates.Moreover,when the loading rate significantly exceeds the unloading rate,stress hystere-sis is observed during the initial unloading moments.Furthermore,greater creep deformation capacity is exhibited by tectonic coal in comparison to primary coal under varying loading con-ditions.The creep trends of coal under nanoindentation conditions are described by the Burgers model,although it is unable to accurately capture the phenomenon of elastic recovery.In con-trast,the creep process of coal under nano-indentation conditions is precisely described by the Fractional Maxwell model.
nano-indentationtectonic coalstructural planerate-dependentcreepcoal and gas outburst
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