Experimental investigation on the spatio-temporal-energy evolution pattern of limestone fracture using acoustic emission monitoring

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.…”

“…The spatial evolution of AE events reflects the crack initiation and propagation inside specimens, and the internal microcracks can be determined by the location of AE event sources. 39,41 To study the internal crack propagation of coal specimens under cyclic loading, the endpoints of the initial loading phase (A), load holding phase (B) and cyclic disturbance phase (C), the peak stress point (D), and the end point of loading (E) were selected for analysis, respectively. According to the Geiger localization algorithm, AE event location was obtained.…”

“…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.…”

Experimental studies of instability process and energy evolution of tunnels under true triaxial stresses: The role of pre-existed flaws

“…Scholars usually use AE (Worley et al, 2019;Zafar et al, 2020), DIC (Fakhimi et al, 2018;Afrazi et al, 2022;Xue et al, 2023a) and energy evolution (Chen et al, 2019;Wang et al, 2020c;Wang et al, 2022) to facilitate the study of crack propagation. The energy evolution analysis of rock is based on the assumption that there is no heat exchange in this process after the external work is done on the rock, and the deformation of the rock is converted into elastic energy and dissipated energy (Xie et al, 2005).…”