Experimental research of mechanical properties on grading cycle loading-unloading behavior of coal-rock combination bodies at different stress levels

To research the mechanical properties of coal-rock combination bodies under multistage and cyclical loading-unloading, a multistage and cyclical uniaxial loading-unloading test (consisting of repeated loading and unloading) was conducted by using the MTS815 System. The results show that the shear failure is the main failure type occurring in the coal-rock combination bodies under multistage uniaxial cyclical loads. Crack propagation in the coal-rock combination bodies under multistage cyclical loads reduces the overall strength of the samples, resulting in more severe failure than in uniaxial compression test. At the first stage of the testing, the strain curve and energy dissipation curve of the samples for a single cycle tend to drop sharply and then go into a slower decline. Moreover, the initial stress shows a positive correlation with dissipate energy and strain. © 2016, Central South University Press. All right reserved.