Micromechanical properties of coals and the response to changes in nanocarbon structure

Abstract

The micromechanical properties of coals are key parameters affecting the development of coalbed methane (CBM). In order to understand the relationship between the micromechanical properties and the nanocarbon structure of coals, high resolution transmission electron microscopy (HRTEM) and nanoindentation were used to investigate the micromechanical properties of vitrinite in different coals and the response to changes in nanocarbon structure. Coals with higher coal rank have greater elastic modulus and hardness. The end-of-loading displacement and creep displacement decrease with the increase of coal rank, both of which have a good negative correlation with the elastic modulus and hardness. Fringe length, degree of orientation, proportion of straight fringes, and proportion of stacks all increase with increasing coal rank. The curvature of the fringes decreases with increasing coal rank. The variation of the nanocarbon structure has an important effect on the micromechanical properties. The nanocarbon structure parameters of fringe length, proportion of straight fringes, degree of orientation, and proportion of stacks have good linear relationships with the micromechanical parameters of elastic modulus and hardness. In addition, this study analyzes the effect of the micromechanical properties of coal on the effectiveness of the proppant. Therefore, the evolution of the nanocarbon structure should be emphasized in future studies on the micromechanical properties of coal.