Acoustic Emission Characteristics and Damage Evolution of Rock under Different Loading Modes

Acoustic emission characteristics and energy evolution law of rock damage process of different pore structures under cyclic loading

The AE and damage characteristics of three types of pore-structured rock under the same working conditions are studied by means of uniaxial cyclic loading and unloading tests. The results suggest that with repeated loading and unloading, AE ringing increases as a "jump", and the denser the structure, the earlier the "jump" occurs. The AE cumulative energy shows a "step" upward trend, but there is a significant difference in the "step" spacing. By comparing the energy distribution of rocks with different pore structures, it can be seen that the smaller the porosity and the smaller the pore size, the greater the energy input and storage, and the earlier the internal failure. Compared with the other two energy-based damage calculation methods, the damage calculation method defined in this paper is closer to the true internal damage level of the rock loading cycle. The NSE value of the modified damage variable calculation method was significantly improved and it was shown that the dissipated energy before pore compaction is the main energy causing damage, after pore compaction the combined effects of dissipated energy and plastic deformation energy result in rock damage.

Mechanical and Acoustic Emission Characteristics of Coal-like Rock Specimens under Static Direct Shear and Dynamic Normal Load

In underground engineering, shear failure is a common failure type in coal-rock mass under medium and low strain-rate disturbance loads. Analyzing the shear failure mechanical properties of coal-rock mass under dynamic normal load is significant. In order to reveal the influence of disturbance load on the shear mechanical properties of coal rock, a dynamic and static load coupling electro-hydraulic servo testing machine was used to conduct the shear tests of coal-like rock materials under dynamic and constant normal load. The amplitude of dynamic load is 10 kN and the frequency is 5 Hz. The damage process of the specimens was detected by the acoustic emission (AE) detection system. The results imply that the shear failure process of coal-like rock materials under constant normal load can be divided into four stages. The normal disturbance decreased the shear strength of the specimens and increased the shear modulus of the specimens. With the increase in normal load, the influence of disturbance on the shear strength of the specimen decreased. By analyzing the AE parameters, it was found that the dynamic load made the internal damage of the specimen more severe during the shear failure process. The damage variable was calculated by AE cumulative energy, and the damage evolution was divided into three stages. The shear failure mechanism of the specimen was judged by RA (rise time/amplitude) and AF (average frequency). It was found that from the elastic deformation stage to the unstable development fracture stage, the proportion of shear fracture increased. When the dynamic normal load was 10 kN and 30 kN, the fracture was mainly shear fracture; When the dynamic normal load was 50 kN, the fracture was mainly tensile or mixed fracture. The dynamic normal load affects the shear strength and failure mechanism. Therefore, the influence of disturbance load on coal-rock mass strength cannot be ignored in underground engineering.