| Acoustic emission of rock is an acoustic signal that reflects the occurrence and development of rock internal micro damage.It plays an important role to study the rock’s inner damage.Due to the difficulty of direct tensile process,therefore,a large number of study about rock compression and indirect tensile acoustic emission were conducted.However,many rocks’ state in the engineering practice is under tension,it is need to research that the direct tensile properties of rock and its acoustic emission characteristics in the tensile process.Discovering the rock direct tension control device,using SANS servo universal testing machine,DS5.0 acoustic emission analyzer and the XL2101 C programmable static resistance strain acquisition system,4 kinds of rock(A group pelious fine grain marble,B group white coarse marble,C group yellow coarse sandstone and H group pink coarse marble)were under direct tensile experiment with acoustic emission,and conducting the single axis and Brazil splitting acoustic emission experiment using the RMT150 test machine,which compared and analyzed under direct experiment,the conclusion is as follows:(1)The uniaxial compressive strength of four type rocks is significantly greater than the direct tensile strength and splitting strength of Brazil.The ratio of pressure and tensile strength is about 10~36 times.The direct tensile strength and splitting strength of Brazil is relatively close,but no obvious correlation,the strength ratio is about 0.6~2 times.There is a big difference about the modulus and Poisson’s ratio under tension and compression,both the deformation modulus and Poisson’s ratio under compression are littlely equal to that or larger than that of uniaxial tension.(2)Direct tensile AE activity law: Based on the different parameters’ size of AE,knowing that the rock internal’s failure severity under the loading process.Early tensile stage(0~10% tensile strength),only a very small sample AE event;In the middle of the stage(10~80% tensile strength),acoustic emission events increased;In the end(close to 100% tensile strength),AE increased rapidly,the amount of counts and a sudden increase in amplitude,amplitude far beyond all pre signal,high AE signal instantaneous energy in macro damage,accompanied by intense sound.Compared with the compression test,the acoustic emission is relatively late,the amplitude and the energy are small,and the signal is not easy to capture before destruction.(3)Based on the direct tension test,the tensile cyclic loading test and the tensile grading loading test were carried out,It is verified that the Kaiser effect and Felicity effect exist in rock under uniaxial tension,Felicity ratio has become a declining trend with the increase of stress,and the rock exists the memory effect under the loading and unloading process with two different path.(4)By using the method of 3D localization method,the arrival-time-difference location of the rock failure process is obtained.And we get the good positioning results.The rock damage’s AE location intensive area and its macro fracture location form a one-to-one relationship.Finally,the microscopic mechanism of rock failure is analyzed from the focal mechanism solution. |
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