The differences of nanoscale mechanical properties among coal maceral groups

Tectonically deformed coals are critically important in coalfield geology structure, coalbed methane exploration and exploitation, and coal and gas outburst. The mechanical property of coal macerals plays a key role in the deformation characteristic of tectonically deformed coals. However, it has not been well investigated the differences of nanoscale mechanical properties among coal macerals. In this work, by employing the depth-sensing nanoindentation, and establishing theoretical analysis and experimental verification, the paper finds the following results: 1) both hardness and elastic modulus are in the order of exinite < vitrinite < inertinite, and the creep displacement follows the order of exinite > vitrinite > inertinite, which correlates closely with macerals’ relevant origin. 2) recovery resistance, Rs, is in the order of exinite < inertinite < vitrinite, which is inherently related to hardness and elastic modulus; according to the differentce of Rs, it can be discovered that the exinite is more prone to produce ductile deformation under the same tectonic stress, while the vitrinite is more likely to develop brittle deformation. 3) based on the difference of energy dissipation ratio, vitrinite < exinite < inertinite, the vitrinite concentration area in coal seam shows higher stability than the other two maceral groups before failure. Therefore, it is necessary to accurately measure the mechanical property differences among coal maceral groups at the nanoscale to better understand the deformation characteristic of tectonically deformed coals.