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Outline
To reveal the loading rate effect of roof fracture behavior, typical mine roof sandstone was taken as the research object. Brazilian splitting tests of five loading rate levels were carried out in the loading rate range of 0.001-10 kN/s. The mechanical behaviors such as tensile strength, fracture characteristics, initiation stress, acoustic emission characteristics and fracture microstructure were analyzed. Based on the distribution of acoustic emission sources, the evolution law of internal damage cracks in the samples under different loading rates was explored. The results show that the tensile strength increases by 0.64 MPa when the loading rate increases by one order of magnitude, but the ratio of crack initiation stress to tensile strength decreases. With the increase of loading rate, this ratio is 40.13%, 36.59%, 32.53%, 26.17% and 15.81% in sequence. When the loading rate increases by one order of magnitude, the average size of the fragments decreases by 0.229 mm, the degree of fragmentation increases, and the size distribution of the fragments develops towards homogenization. The acoustic emission source at low loading rate mainly appears along the macroscopic fracture surface, while at high loading rate, the distribution of acoustic emission source is more dispersed due to the initiation and propagation of cracks from multiple dispersed stress concentration areas. With the increase of loading rate, the transgranular phenomenon at the fracture surface becomes more and more significant, transitioning from a single crack and straight form at low loading rates to multiple cracks and complex forms at high loading rates.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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