Damage evolution and failure behavior of coal-rock combination subjected to different cyclic loading paths and loading rates: Insights from energy-driven effects

Abstract

In this study, a uniaxial cyclic compression test is conducted on coal-rock composite structures under two cyclic loads using MTSE45.104 testing apparatus to investigate the macro-mesoscopic deformation, damage behavior, and energy evolution characteristics of these structures under different cyclic stress disturbances. Three loading and unloading rates (LURs) are tested to examine the damage behaviors and energy-driven characteristics of the composites. The findings reveal that the energy-driven behavior, mechanical properties, and macro-micro degradation characteristics of the composites are significantly influenced by the loading rate. Under the gradual cyclic loading and unloading (CLU) path with a constant lower limit (path I) and the CLU path with variable upper and lower boundaries (path II), an increase in LURs from 0.05 to 0.15 mm/min reduces the average loading time by 32.39% and 48.60%, respectively. Consequently, the total number of cracks in the samples increases by 1.66-fold for path I and 1.41-fold for path II. As LURs further increase, the energy storage limit of samples expands, leading to a higher proportion of transmatrix and shear cracks. Under both cyclic loading conditions, a broader cyclic stress range promotes energy dissipation and the formation of internal fractures. Notably, at higher loading rates, cracks tend to propagate along primary weak surfaces, leading to an increased incidence of intermatrix fractures. This behavior indicates a microscopic feature of the failure mechanisms in composite structures. These results provide a theoretical basis for elucidating the damage and failure characteristics of coal-rock composite structures under cyclic stress disturbances.

Keywords

coal-rock composite samples / cyclic loading / loading and unloading rates / RA-AF correlation / macro-micro damage features / failure behavior

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