Experimental study on damage and failure characteristics of similar materials with prefabricated fracture sandstone

In order to reveal the meso-damage mechanism of the physical simulation of coal and rock dynamic disasters,the YYW-Ⅱ uniaxial compression tester and PCIE-8 acoustic emission(AE) monitoring system were used to explore the mechanical properties,failure characteristics,and damage evolution characteristics of samples with different lengths of prefabricated single fracture under uniaxial compression. The results show that as the length of the prefabricated single crack increases：the peak strength and residual strength of the sample decrease linearly from 746.84 kPa and 199.117 kPa to 597.643 kPa and 110.375 kPa respectively,while the peak axial strain and initial compaction strain increase linearly from 0.018 18 and 0.002 40 to 0.023 61 and 0.005 32 respectively. The prefabricated fractures have an increasing influence on the failure mode and characteristics of the sample,and the dominant failure mode of the sample gradually changes from shear failure to longitudinal tensile failure through the middle of the fracture. The accumulative acoustic emission(AE) events and the accumulative energy of the samples showed a gradual decreasing trend,from 465 and 82 278 J to 306 and 54 152 J respectively,and AE event activity gradually weakened. The damage evolution of the sample has experienced three stages：initial damage accumulation,stable damage development and accelerated damage development and the damage increases during the stable development and accelerated development stages from 0.621 and 0.734 to 0.655 and 0.817，respectively. The prefabricated single crack has a greater influence on the damage evolution of the specimen in the accelerated development stage than in the stable development stage,and the maximum damage variable difference of each sample is 0.017 and 0.042，respectively in the stable development and the accelerated development stage of damage. During the loading process,the mechanics,AE,and damage characteristics of similar materials under load have a strong correlation,and the mechanical changes cause damage changes,which in turn have a strong causal relationship with the changes of AE parameters. The characteristic parameters of AE events can accurately describe the damage and failure characteristics of similar materials. The research results provide a basic reference for the exploration of the mechanism of coal and rock dynamic disasters.