Energy distribution and criticality characteristics analysis of shale Brazilian splitting test

In order to clearly understand the energy statistical distribution of brittle shale during tensile test,a research has been conducted to obtain the distribution law of the destruction energy and energy statistics in the local stress,thus providing a theoretical foundation for the in-situ fracturing mechanism. This paper selects the calcareous shale from the Longmaxi Formation of the Southern Sichuan Basin to carry out Brazilian splitting ( indirect tensile) test detected by the acoustic emission probe (AE). There are three settled loading rates which are 0. 005,0. 05 and 0. 5 mm / min re- spectively. The results are as follows:① The probability density function of energy conforms to the power-law distribu- tion under different loading rates, that is and it follows the time scale-free distribution function as power-law form. ② The probability density function of energy in the local stress also conforms to the power-law distribution,which have a good fit of this distribution to the power-law distribution. The energy probability distribution curves under different stress stages flow towards overall energy probability distribution. ③ The system comes into a critical state when the ap- plied stress reaches about the 0. 9σmax . The energy distribution curve and exponent distribution curve are close to the energy distribution curve and exponent value distribution curve at this stage during the whole loading process,and a gradual overlap takes place. ④ The test results are in conformity with the numerical simulation results of fiber bundle model. When the applied stress σ reaches to 90% of the specimen failure stress,the branching ratio ξ increases sharp- ly until the rock failures. The results above can well validate the criticality characteristics.