Study on the acoustic and thermal response characteristics of coal samples with various prefabricated crack angles during loaded failure under uniaxial compression

In this study, uniaxial compression tests were conducted on coal samples with different-angle prefabricated cracks. Based on the test results, the effects of prefabricated crack angles on the mechanical properties, failure modes and acoustic and thermal characteristics of the samples during loaded failure were analyzed. The following research results were obtained: the prefabricated crack angle significantly influences the mechanical properties of coal samples. Both the peak stress and the peak strain increase with the increase of the prefabricated crack angle, and the relationships between them and the prefabricated crack angle satisfy quadratic functions. The fracture types of prefabricated fracture coal samples are wing-shaped cracks, inverse wing-shaped cracks and split fracture. For example, when alpha=90 degrees, the coal sample experiences splitting failure. The infrared radiation temperature (IRT) and acoustic emission (AE) responses exhibit obviously distinct characteristics in different stages. The states of crack propagation in the loaded failure process can be clearly obtained by means of infrared thermal images and AE location. With the increase of the prefabricated crack angle, the change in average infrared radiation temperature and the peak AE counts vary in a similar trend, both decreasing first and increasing later.