Mechanical characteristics and dynamic damage evolution mechanism of coal samples in compressive loading experiments

To achieve the qualitative and quantitative damage expression, coal samples within original cracks were selected to conduct uniaxial compressive loading experiments. During this process, acoustic emission signals were collected by AEwin Test for Express-8.0 and cracks evolution were captured by video camera. The results showed that the larger the initial damage, the lower the uniaxial compressive strength and elastic modulus of coal samples. When coal samples were subjected to uniaxial compression, the primary cracks closed firstly. Then friction phenomenon might generate due to sliding along the cracks surface and the deflection might occur at the center of cracks. Finally, original cracks expanded and new cracks formed and propagated to cause sample fracture, all which leaded to acoustic emission events. AE counts and accumulated counts changed with time, which corresponded well with stress-strain. Therefore, the value of AE counts and the trend of accumulated counts qualitatively explained the damage evolution laws of loaded coal. Further, based on the damage theory of acoustic emission counts, the quantitative damage variable was proposed and calculated. What's more, the force analysis near the cracks surface at the initial loading process was explained and the cracks dynamic evolution during the whole compressive loading process was discussed. It was helpful to understand the damage evolution mechanism of coal samples.