温度冲击下煤的微观结构变化与断裂机制

Microstructure evolution and fracturing mechanism of coal under thermal shock

为研究温度冲击下煤的微观结构变化及其损伤断裂机制,以干燥颗粒煤为研究对象,分别开展了煤样的冷冲击和热冷冲击试验。利用扫描电镜(SEM)观测图像结果,分析对比了两种温度冲击前后煤样微观形貌、裂缝分布、开裂和延伸情况,结合断裂力学理论分析了煤样内部微裂缝的开裂机制和扩展方向,并通过ANSYS有限元软件模拟了微裂缝扩展时的应力场和位移场的分布情况,揭示了煤样的断裂机制。研究结果表明,两种温度冲击对煤的结构均造成了不同程度的破坏,温度冲击所形成的热应力最终导致了原始裂纹和新生裂纹的扩展和延伸;温度冲击下所产生的裂纹形式主要有沿晶裂纹、穿晶裂纹、翼型裂纹、交叉裂纹、枝须状裂纹和网状裂纹;分析结果表明,温差愈大,所产生的温度热应力愈大,热冷冲击所产生的裂缝的数量更多、扩展更充分,对煤样的破坏更严重,因此,热冷冲击的破煤效果更好。

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.