Abstract: To study the microstructure change of coal and its damage and fracturing mechanism under temperature shock, cold impact and hot-cold impact tests were carried out on dry granular coal. The micro-morphology, fracture distribution, cracking and extension of coal samples before and after temperature impact were analyzed and compared by scanning electron microscopy (SEM). The cracking mechanism and propagation direction of micro-cracks in coal samples were analyzed based on fracture mechanics theory. The distributions of stress and displacement fields during micro-crack propagation were simulated by ANSYS finite element software to reveal the fracturing mechanism of coal samples. The results showed that the structure of coal was destroyed by two types of temperature shocks, and the thermal stress induced by temperature shocks eventually led to the expansion and extension of the original crack and the new crack. The main types of cracks induced by temperature impact were intergranular crack, transgranular crack, airfoil crack, cross crack, dendritic whisker crack and mesh crack. It is revealed that a bigger temperature difference results in a higher thermal stress. Hot-cold impact can generate more cracks and more extensive crack propagation than cold impact, leading to more serious damage of coal samples. Therefore, the hot-cold impact has better coal breaking effect than the cold impact.

Key words: thermal shock, microstructure, fracture mechanism, stress intensity factor, coal breaking effect