Mechanical Behaviors and Acoustic Emission Fractal Characteristics of Bump-Prone Coal under Different Loading Rates

Abstract

Coal and rock dynamic disasters occur frequently in deep coal mining. The loading rate affects the mechanical properties and behaviors. Uniaxial compression acoustic emission (AE) tests of bump-prone coal under various loading rates were carried out, and the mechanical properties, AE spatiotemporal evolution, and spatial fractal characteristics were analyzed. The experimental results indicate that the uniaxial compressive strength is positively related to the loading rate, and the elastic modulus increases before decreasing with the loading rate. The failure strain is positively related to the loading rate, and the percentage of the compaction phase relative to the pre-peak phase decreases with the loading rate. The hit rate, absolute energy, AE events, and amplitude evolution of coal samples under various loading rates are the same, and the maximum of AE absolute energy and hit rate is positively related to the loading rate. The spatial evolution of AE events of coal samples under various loading rates is the same, showing a “slow increase → slow increase → fast increase → rapid increase → slow increase” trend. The spatial fractal dimension ranges from 2.1 to 2.9, and the evolution of coal samples under various loading rates is the same, exhibiting a downward trend.

Failure characteristic and acoustic emission spatio‐temporal evolution of coal under different cyclic loading rates

“…The cylindrical‐covering method is commonly used to obtain the spatial fractal dimension of cylinder samples, 24,41,44 and the spatial fractal dimension of coal under various cyclic loading rates was obtained. Figure 11 shows that the spatial fractal dimension of coal samples under various cyclic loading rates was the same, and generally presented a downward trend, which is the same as previous results under the uniaxial compression tests 24,41,44 . The fractal dimension of the initial loading phase was high, mainly distributed in 2.7–2.9, indicating that the initial fissures and pores in the coal sample were evenly distributed, and the AE events generated were evenly distributed.…”

“…25,42,43 The spherical covering method, projection circle covering method, and cylindrical covering method are used to obtain the spatial fractal dimension of AE events. The cylindrical-covering method is commonly used to obtain the spatial fractal dimension of cylinder samples, 24,41,44 and the spatial fractal dimension of coal under various cyclic loading rates was obtained. Figure 11 shows that the spatial fractal dimension of coal samples under various cyclic loading rates was the same, and generally presented a downward trend, which is the same as previous results under the uniaxial compression tests.…”

“…Figure 11 shows that the spatial fractal dimension of coal samples under various cyclic loading rates was the same, and generally presented a downward trend, which is the same as previous results under the uniaxial compression tests. 24,41,44 The fractal dimension of the initial loading phase was high, mainly distributed in 2.7-2.9, indicating that the initial fissures and pores in the coal sample were evenly distributed, and the AE events generated were evenly distributed. At the load-holding phase, the fractal dimension decreased slowly, mainly distributed in 2.6-2.8, which is mainly due to the microcrack initiation inside the coal sample.…”

Investigation and Application of Fractals in Civil Engineering Materials

“…Coal and rock dynamic disasters occur frequently in deep coal mining. In the work conducted by Liu et al [2], the uniaxial compression acoustic emission (AE) tests of bumpprone coal under various loading rates were carried out, and the mechanical properties, AE spatiotemporal evolution, and spatial fractal characteristics were analyzed. The results indicate that the uniaxial compressive strength is positively related to the loading rate, and the elastic modulus increases while the loading rate decreases.…”