Title: evolution law of internal microstructure and surface crack of coal sample under local load
Authors: Zhao Hongbao 1,2, Wang Tao 1, Su Boyi 1, Cheng Hui 1, Liu Shaoqiang 1, Li Yang 1
Author:
1. College of energy and mining, China University of mining and technology, Beijing 100083;
2. Key Laboratory of mine geological disaster mechanism and prevention and control, Shaanxi Geological Survey Institute, Xi'an 710054, Shaanxi Province
Abstract:
In order to study the internal microstructure and surface crack evolution of raw coal and briquette samples under local load, the compression tests of raw coal and briquette samples under different loading areas were carried out, and the real-time images of ultrasonic wave velocity and surface crack change of samples during loading were obtained, based on the defined damage factor and fractal theory, The results show that the stress-strain curves of the two samples under local load have typical stage characteristics, and the deformation of the coal sample in the compaction stage is larger than that of the coal sample, and the compressive strength of the two samples increases linearly with the increase of the loading area, The ultrasonic wave velocity curve of briquette specimen under uniaxial compression is short of the initial loading strengthening stage, which only includes two stages: loading weakening zone and loading instability zone; local load does not change the three-stage characteristics of coal specimen damage, but only shortens the duration of each stage; under local load, the surface crack propagation direction of raw coal specimen is approximately parallel to the loading direction, The main crack is located in the interface area between the loading area and the non loading area; the direction of the surface crack growth of the briquette sample is at a certain angle with the loading direction, and the cracks are all in the loading area; the surface cracks of the two kinds of coal samples have obvious fractal characteristics under the local load, and the fractal dimension of the raw coal surface and the strain have a cubic function law, The relationship between the fractal dimension and the strain of the briquette surface is a quadratic function law. The fractal dimension and the loading area of the two samples are quadratic function law near the failure time, Et al. Internal microstructure and surface fracture evolution of coal samples under local load [J]. Journal of China University of mining and technology, 2020,49 (2): 227-237
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