Experimental Research on Microscopic Shear Failure and Acoustic Emission Characteristics of Coal or Rock
|Course||Safety Technology and Engineering|
|Keywords||rock mechanics shear microscopic failure acoustic emission crack evolution|
Macroscopic rupture instability of rock is closely related to the distribution of microfissure and initiation, extension and aggregation of crack during the deformation of rock. And the alteration of acoustic emission signal intensity can reflect the degree of microscopic damage of rock during the deformation. Therefore, experimental study is made on microfracturing progress of crack of sandstone and moulded coal, their distribution characteristics after failure and acoustic emission characteristics under shear loading condition by independent developmental coal or rock microscopic shear testing device and PCI-2 type of acoustic emission testing system. Simultaneously,it is also researched on temporal and spatial evolution law of crack and acoustic emission characteristics of sandstone and moulded coal under the different loading rates, the different moisture states, and the different normal stresses in shear loading. The main results obtained are as follows:(1) The surface fracturing of sandstone is after peak stress under different loading rates, but it will be appear before peak stress in moisture contents of 50.03%, 89.17% and 100.00%, as well as normal stresses of 1.5MPa, 3.0MPa, 4.5MPa and 6.0MPa. Crack of sandstone generally produced in the end of specimen. Furthermore,in the process of rupture failure of sandstone,it is produced both intergranular fracture and transgranular fracture,however,the main microfracturing progress is produced in grain boundary and cement. The conspicuous microfracturing progress of moulded coal is different from sandstone under different loading rates, crack initiate in the end or middle of specimen, but the rupture pattern is unconspicuous.(2) The spreading direction of microcrack of sandstone and moulded coal has irregularity,which has bias in some degree compared with predetermined shear plane. There are also some secondary cracks formed in the proximity of main crack, but the width and length of which are smaller. However, the crack shape of moulded coal is more complex, and the width of fracturing is larger than sandstone.(3) The peak of acoustic emission hit rate of sandstone and moulded coal always appears later than peak stress does. For sandstone, the time difference between them decreases with the increase of loading rate, but increases with the increase of moisture content and normal stress. Although the result of moulded coal is the same with sandstone in different loading rates, the lag is much larger than sandstone. (4) Most acoustic emission signals appear after peak shear stress of sandstone and moulded coal. The leap point of acoustic emission signal of sandstone is in advance when loading rate and moisture content increase, but it will delay with the increase of normal stress. The percentage of AE number increases with the increase of loading rate, but decreases with increase of moisture content and normal stress at peak stress and surface fracturing point of sandstone. Then the acoustic emission signal of moulded coal is lower. There is not specially conspicuous leap point during the failure. The larger the loading rate is, the earlier the acoustic emission activity occurs, but the acoustic emission activity of moulded coal falls behind sandstone.