Time-varying multifractal of acoustic emission about coal samples subjected to uniaxial compression

To explore the causes of acoustic emission (AE) mechanisms during different loading stages, the collected coal samples were subjected to uniaxial compression, and the AE counts signals were collected to analyze time-varying AE laws during loading process. Based on the time-varying multifractal theory, the multifractal characteristics with load and time were researched. The results showed that time-varying characteristics of AE corresponded well with load - time, which could reflect cracks evolution and loading process. And during different loading stages (from 20%σc to 80%σc), Δα narrowed gradually, which were related with the number and mode of fractures evolution. The time-varying multifractal characteristics revealed AE mechanisms and the proportion relation between strong and weak AE signals. Δα changes with time explained fractures compaction in different scales at the initial stage, cracks sliding and friction during the elastic deformation stage, and cracks expanding and linking at the fracture stage, while the other multifractal parameter (Δf) with time could reflect strong AE signals dominated at the initial and later stages, and the proportion of strong AE signals was almost equal to that of weak AE signals during the elastic deformation stage. The time-varying multifractal laws of AE counts about coal loading will provide significant guide to the early warning of coal deformation or fracture underground coal mines.