Relationship between fractal meso-structural and mechanical characteristics of lump coal under uniaxial compression at different temperatures.

Coal breakage characteristics have significant effects on the clean utilization of coal. The mechanical properties of Shenmu (SM) coal, Hongshaquan (HSQ) coal and Wucaiwan (WCW) coal under uniaxial compression were tested by a self-designed bench at 90 °C, 120 °C, 150 °C and 180 °C. The results show that the mechanical parameters overall decrease with the increase of temperature (T, °C) except that SM coal has an increasing trend from 120 °C to 180 °C due to thermal expansion of coal matrix and moisture inside closed pores. The compressive strength (σ m , MPa) of SM coal at 120 °C decreased by 43% compared with it in 90 °C. By means of fractal theory, these mechanical properties can be reflected by the meso-structural characteristics of coal surface. The fractal dimension (D) generally possesses a positive correlation with the stress (σ, MPa). In initial segments, the curves of some coal samples are relatively stable due to compaction and compressive resistance. Two dimensionless parameters, relative fractal dimension (D r) and relative stress (σ r), were introduced to represent the relationship of meso-structural and mechanical properties quantitatively. It is shown that the relative fractal dimension rises quickly when the relative stress is above 0.75, and the relationship of the two dimensionless parameters can be described. • Mechanical properties of three kinds of coals at different temperatures were studied. • The evolution of coal surface during the loading process was calculated with the help of high speed camera and fractal theory. • The nonlinear relationship between meso-structural and mechanical properties was formulated. [ABSTRACT FROM AUTHOR]