Dynamic characterization of pressurized coal under cyclic weak impact loading.

12 , the counting box-counting dimension with the number of changes in the number of weak impacts showed a trend of decreasing and then increasing, which is consistent with the trend of cumulative damage, indicating that the first three weak impacts are dominated by compression and densification, the internal densification of the specimen increases, the degree of impact fragmentation reduces, and the complexity of the profile decreases; while the fourth weak impact is dominated by the role of the damage, the specimen cracks increase, the pore increases, the degree of impact fragmentation increases, and the complexity of its profile rise.

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It is analyzed that there are macroscopic and microscopic cracks in the specimen, which are mainly compressed under the action of stress wave and three-dimensional static loading, so that the mineral crystallites inside the specimen occlude to enhance the spacing and further reduce the spacing, which inhibits the microcracks from sprouting and expanding, and the external manifestation of the overall stiffness rises, and the modulus of elasticity shows an increasing trend.

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