Mechanical heterogeneity characterization of coal materials based on nano-indentation experiments

Abstract

To investigate the complex macro-mechanical properties of coal from a micro-mechanical perspective, we have conducted a series of micro-mechanical experiments on coal using a nano-indentation instrument. These experiments were conducted under both dynamic and static loading conditions, allowing us to gather the micro-mechanical parameters of coal for further analysis of its micro-mechanical heterogeneity using the box counting statistical method and the Weibull model. The research findings indicate that the load – displacement curves of the coal mass under the two different loading modes exhibit noticeable discreteness. This can be attributed to the stress concentration phenomenon caused by variations in the mechanical properties of the micro-units during the loading process of the coal mass. Consequently, there are significant fluctuations in the micro-mechanical parameters of the coal mass. Moreover, the mechanical heterogeneity of the coal at the nanoscale was confirmed based on the calculation results of the standard deviation coefficient and Weibull modulus of the coal body’s micromechanical parameters. These results reveal the influence of microstructural defects and minerals on the uniformity of the stress field distribution within the loaded coal body, as well as on the ductility characteristics of the micro-defect structure. Furthermore, there is a pronounced heterogeneity in the micromechanical parameters. Furthermore, we have established a relationship between the macro and micro elastic modulus of coal by applying the Mori-Tanaka homogenization method. This relationship holds great significance for revealing the micro-mechanical failure mechanism of coal.

Keywords

nano-indentation experiment / micromechanics / heterogeneity characterization / coal

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