Experimental study on compression-shear fracture evolution process of locked segment of rock-like based on multivariate parameters

Abstract Locked segment of rock-like material specimens with different brittleness index were prepared by combining materials in different ratios. Compression-shear tests of rock-like material specimens with different brittleness degree were carried out by acoustic emission and Laser Doppler Vibrometer measurement. The fracture evolution process of the specimen was divided into three stages through the displacement-time curve: compaction stage and elastic deformation stage, constant deformation stage and accelerated deformation stage. The natural frequency responded obviously at the boundary point of the constant deformation stage and accelerated deformation stage, the point of natural frequency steeply dropped corresponds to the starting point of constant deformation stage, which is defined as the damage point. The point of substantial increase in the natural frequency corresponds to the starting point of accelerated deformation stage, which is defined as expansion point. There were obvious critical instability information before the failure of specimens: The natural frequency showed rise, steep drop and stable jitter; The ringing count rate and energy rate increased near the critical instability point; The b-value continued to decrease at a low level before the peak strength. Tensile failure was the main failure mode of the three specimens with different brittleness degree, the tensile failure degree increased with the increase of brittleness degree. The energy released by the specimen at failure moment increased with the increase of brittleness degree, and the b-value decreased with the increase of brittleness degree. The degree of brittleness is one of the important indexes to study the locked segment.