三轴高周载荷下煤岩疲劳损伤破裂演化特征研究OA

To investigate the effects of stress level and loading frequency on the evolution of fatigue damage and fracture in coal,triaxial high cycle load tests with acoustic emission(AE)monitoring were conducted.The AE responses and macro-meso fracture characteristics of coal under different conditions were analyzed.The results indicate that with a fixed lower-bound stress,a higher upper-bound stress leads to more significant fatigue crack development and more active AE responses.The specimen successively undergoes initial damage in the linear loading stage,followed by slight,moderate,and severe fatigue in the cyclic loading stage ultimately leading to failure.An increase in loading frequency accelerates the initiation,propagation and coalescence of microcracks,and significantly enhances AE activity,with the energy count rate and ringing count rate exhibiting highly synchronous variations.In contrast to conventional triaxial compression,coal under high cycle load presents multi-directional shear failure,with more complex crack distribution,more uniform fragmentation and more dispersed deformation at the microscale.AE parameters can effectively characterize the evolution process of fatigue damage in coal.