Study on the evolutionary characteristics of strain energy on crack propagation in coal and rock under bending load

Abstract

The failure of coal mine overburden is mainly caused by fractures under bending loads. The energy evolution characteristics of coal and rock fractures are closely related to coal mine disasters such as rock burst. To obtain the characteristics of energy release and accumulation of coal and rock under bending load, three‐point bending tests of coal, mudstone, and sandstone were carried out respectively. The strength characteristics and fracture propagation process of coal and rock under bending load were studied. The strain energy evolution rules of coal and rock were calculated and obtained. The fracture mechanism of coal and rock was discussed by analyzing the critical strain energy release rate. The results show that the fracture complexity of sandstone and mudstone is greater than that of coal. The microstructure and its directivity in coal and rock indirectly affect their fracture characteristics through the elastic modulus characteristics. The distribution of parameters such as peak load of fracture, fracture energy, and crack length of coal and mudstone samples is discrete, while that of sandstone samples is concentrated. The deformation energy density of coal and rock basically shows a linear increase trend at the prepeak stage. The deformation energy density evolution characteristics at the postpeak stage are mainly affected by the load drop. It is important to establish the internal relationship between the meso structural characteristics and macro mechanical properties for solving engineering problems.