Damage evolution of rock containing prefabricated cracks based on infrared radiation and energy dissipation

This study aims to study the damage evolution characteristics of rock mass containing prefabricated cracks with different angles. First, similar material proportioning tests were carried out referring to the composition and mechanical properties of coal seam roof in Xin-ji No. 1 Coal Mine based on the analog simulation theory. Af-terwards, macroscopic cracks with different angles were prefabricated on the specimens. During the uniaxial loading experiments, the infrared radiation information of the specimen surface was obtained using an infrared monitoring system. Moreover, the damage variables were defined based on the accumulated infrared radiation temperature and the proportion of dissipative strain energy in the energy evolution. The results show that with the increase in prefabricated crack's dip angle, the brittleness of the rock mass diminishes; the closing strain of the prefabricated crack decreases; the stress concentration location of the crack tip starts to spread outward from the center of the specimen; and the failure changes from a tensile-shear composite mode to a tensile splitting mode. The infrared radiation temperature on the specimen surface fluctuates; specifically, it falls first and then rises. The abrupt change of the maximum infrared radiation temperature near the peak stress is significant, and this change reaches the maximum when the dip angle of the prefabricated crack is 45 degrees. In addition, the damage evolution process of the rock mass can be roughly divided into three phases: initial damage, stable damage and accelerated damage. The stresses calculated from the defined damage variables have the same trend with the measured stresses, with a correlation of over 0.9, so it can well characterize the progressive evolution process from the crack emergence, expansion to failure. The research presented in this paper can provide a theoretical support for the early warning of coal-rock dynamic disaster.