AE-infrared Characteristics And Damage Evolution Generated From Rock Under Variable Angle Shear

Instability prediction and damage assessment are important issue for urgent solution in therock mechanics, and shear failure is one of the most common forms of rock mass catastrophe. Alarge number of experimental and theoretical studies show that transfer phenomena betweenmechanical and thermal energy appears from rock accompanied by energy dissipation under theload. Acoustic emission (AE) is directly related to micro fracture generated from rock thatproportional relationship exists between the AE parameter and rock damage. Infrared radiationreflects the distribution characteristics of rock surface temperature field. Therefore, study ondamage evolution and stability of rock mass under shear load is particularly important, which canprovide the theory basis to the instability disaster monitoring and early warning for rock mass.In this paper, the granite and sandstone were as the object of study, and synchronousexperiment about acoustic emission and infrared radiation under three kinds of shear angle (45,60, and75) was started. Frequency characteristics of acoustic emission, changes of infraredradiation, and damage evolution in the loading process of rock were analyzed. The main resultswere as follows.1. Mechanical properties of granite and sandstone under different shear angle were studiedfrom the two aspects of shear strength and deformation characteristics. Coulomb yield conditionand shear failure characteristics of granite and sandstone could be obtained.2. Evolution characteristics of AE counts and energy in different stages of rock were summedup through the analysis of AE parameters under different shear angle. Under different shear angles,all the specimens had experienced four stages, which included pressure closed, elastic, plastic, anddestruction, and AE activities kept little difference in same stage. AE counts and energy were rapidgrowth when explicit cracks or damage appeared on rock, and AE energy showed a "quiet period"before rock failure. With the increase of shear angle, AE energy was better able to predict the rockfailure than AE counts.3. Based on Welch power spectrum estimation and empirical mode decomposition (EMD),the evolution properties of AE peak frequency, energy factor and EMD energy entropy with theloading time under different shear angle.4. Characteristics of the average infrared radiation temperature (AIRT) and infraredthermography generated from rock rupture process under different shear angle were analyzed indetail. This paper studied the relationship between axial load, shear angle and AIRT-time curve. The results show that abnormal high temperature phenomenon was more apparent with theincrease of shear angle.5. By using AE ringing cumulative count, temperature change point cumulative countrespectively to determine the overall damage variable and surface damage variable of rockmaterials, damage characteristics of granite and sandstone under different shear angle wereanalyzed. At the same time, relationship between the ultimate shear load and damage variablewould be clear. Based on internal connection between the overall damage and surface damage ofrocks in the shear load, the point that stage and precursor of overall damage were more obviousthan these of surface damage was proposed.