Study On Strain And Damage Temporal And Spatial Evolution And Fracture Precursor Identification Of Rock

In this paper,the time series characteristics of strain and acoustic emission signal under different loading conditions are studied by setting up strain-acoustic emission testing system,and the damage model based on acoustic emission counting is established,The relationship between damage and stress is studied,and the crack evolution process in the failure process of specimen is described experimentally.An elastoplastic constitutive model based on D-P criterion is established and verified by numerical simulation.Critical slowing-down theory is used to identify the failure precursor information of strain,and R/S theory is used to identify the failure precursor information of AE count and energy.The following basic conclusions can be drawn:(1)Based on the results of the strain test,under uniaxial loading conditions,the strain is greatly influenced by the fluctuation of external load.When the load fluctuates,the strain also changes violently.The spatio-temporal characteristics of the strain at the measured points can be divided into three categories: 1.The strain increases gradually with the increase of load or time.2.As the load or time increases,the strain decreases first and then increases;3.As the load or time increases,the strain increases first and then decreases.Under uniaxial loading conditions,in the stage of force loading,the measured strain changes with the change of external load,but in the stage of force holding,the strain tends to be stable.(2)Based on the results of acoustic emission testing,along with the loading,the AE signal becomes active gradually,and the AE and count increase suddenly when the specimen is unstable and damaged.At each stage of loading,the acoustic emission count and energy of the specimen first increase and then decrease with the increase of axial stress.At the force holding stage,the Acoustic emission count and energy of the specimen decrease to zero.The developing direction is similar to the loading direction,the sample eventually showed brittle failure..According to the established damage assessment model,the damage and load of the specimen are in accordance with the exponential function.(3)Based on the numerical simulation results,it is shown that the volumetric strain and the elastic strain energy density increase with the loading.Under the same condition of static load,the area of strain localization zone,the strain intensity,the elastic strain energy and the damage degree of the model increase with the increase of the disturbance intensity.(4)Based on the critical slowing-down principle,the variation of the time sequence of the Quantitative analysis strain variance,and the identification of the premonitory information of the instability and failure of the specimen using the rescaled range(R/S)method are studied.The variance of the strain at the test point begins to increase or the volatility of the test point increases,and then increases rapidly or suddenly when the adjacent sample ruptures,The feasibility of rock burst monitoring and early warning research based on internal strain is verified.The "quiet period phenomenon" appears in the acoustic emission signal before instability and failure,and the "quiet period phenomenon" can be used as the "precursor information point",At the same time,the number of AE and Hurst exponent increased to the maximum and the fractal dimension DF decreased to the minimum.It can be used as a precursor to the instability of the sample.