Energy distribution and fractal characterization of acoustic emission (AE) during coal deformation and fracturing

In this paper, the acoustic emission (AE) signals of coal ruptures were evaluated under the condition of uniaxial compression, and then the spectral, energy and fractal features of the AE waveform under different stress levels were analyzed. Results show that coal damage is progressive under loading and that the corresponding AE is paroxysmal. The AE signals are closely related to the load and deformation of coal rock. AE counts reaches the maximum at the peak stress and it reduces once the coal ruptures. During the compaction load stage, the coal structure is stable, it produces only bits of AE events with low frequency and spectrum. In addition, the proportion of low-frequency band energy is greater, and the correlation dimension is the maximum. However, as the loading progresses, the coal becomes unstable, the frequency and high-frequency band energy increase. Whereas, the correlation dimension decreases. Near the dilatation of coal volume, the AE frequency, amplitude and high-frequency band energy reach the peak values, and the correlation dimension decreases to a minimum value. At the stress peak, coal ruptures, the AE frequency reduces, low-frequency band energy increases, and the correlation dimension reaches to a low value. During the initial load time, AE is primarily influenced by small energy events. Near the dilatation of coal volume, the proportion of large-energy incidents primarily affects the AE characteristics. At the stress peak, the crack size primarily influences these characteristics. Before the peak load, the main deformation of coal is fracturing, and frictional force dominates. The AE waveform characteristics can be used to evaluate the process of coal rupture and the form of ruptured coal. (C) 2018 Elsevier Ltd. All rights reserved.