Experimental Study On Failure Characteristics Of Large-scale Rock-like Rocks Under Cyclic Loading

During the mining process,the rock is often subjected to cyclic loads and accumulated damage,resulting in the phenomenon of fatigue failure.Many scholars at home and abroad have carried out a series of experimental studies on the mechanical failure characteristics of rock under cyclic loading,but the main research objects are small-sized specimens,and there are few experimental studies on large-sized rock specimens.In this paper,the self-made impact disturbance surrounding rock test system CX-8568,combined with the acoustic emission monitoring system,is used to explore the failure characteristics of large-sized rock-like rocks under cyclic loading.The main conclusions obtained are as follows:(1)The uniaxial compression test was carried out on the large-sized rock-like specimens,and the mechanical parameters of the large-sized rock-like specimens were obtained.The fatigue threshold of large-sized rock-like specimens is calculated by the ratio of yield stress to peak stressσ_c.(2)When the stress amplitude remains unchanged,the axial deformation characteristics of large-scale rock-like specimens under static stresses of 0.8σ_c,0.85σ_c,and 0.9σ_care explored.The results show that when the static stress is 0.8σ_c,the axial deformation characteristics of the specimen are divided into the initial stage,the uniform velocity stage and the instability failure stage.When the static stress is 0.85σ_cand 0.9σ_c,the development characteristics of axial deformation are divided into uniform stage and unstable failure stage.Axial deformation characteristics of the specimen.The results show that the axial deformation of the specimen with a stress amplitude of 0.15σ_cis divided into the initial stage,the constant velocity stage and the instability failure stage.When the stress amplitudes are 0.2σ_cand0.25σ_c,the axial deformation is divided into a uniform stage and an unstable failure stage.(3)The ultimate deformation of large-size rock-like specimens under uniaxial compression is close to the ultimate strain of large-size rock-like specimens under cyclic loading.Different static stresses and different stress amplitudes have little effect on the ultimate strain of large-sized rock-like specimens when they fail.(4)Under the condition of constant stress amplitude,the fatigue life of large-sized rock-like specimens shortens with the increase of static stress;under the condition of constant static stress,the fatigue life of large-sized rock-like specimens varies with the stress amplitude.decreases as the value increases.The reduction of fatigue life of large-sized rock-like specimens is not proportional to the increase of static stress and stress amplitude.The fatigue life of large-sized rock-like specimens under cyclic loading can be roughly estimated based on the strain rate of the specimen.(5)The failure mode of large-size rock-like specimens under cyclic loading is mainly splitting failure.Under the condition of constant stress amplitude,the number of main cracks increases with the increase of static stress when the large-size rock-like specimen fails,and the degree of fracture increases with the increase of static stress;The fracture degree of rock-like specimens increases with the increase of stress amplitude.(6)Acoustic emission monitoring results show that there are two stages in the change of AE cumulative ringing counts during the failure process of large-sized rock-like specimens under cyclic loading,namely slow growth stage,violent growth stage and initial stage,stable stage,stage of rapid growth.The acoustic emission localization results of large-sized rock-like specimens under cyclic loading show that when the static stress remains unchanged,the specimens with three stress amplitudes of 0.15σ_c,0.2σ_c,and 0.25σ_chave cracks in the middle,and the acoustic emission event The number increases as the stress amplitude increases.