Cement mortar specimens are used to simulate the fracture of rock material under uniaxial compression test, using the ultrasonic instrument measurement test process, the waveform and wave velocity results along with the change of specimen fracture extension are obtained. Experimental results show that at 0 MPa, there are micro-defects in the specimen, leading to the irregular change of the waveform of the measuring points 4# and 5#;At 1 - 4 MPa, there is no crack on the surface of the specimen, the waveform of ultrasonic wave is stable, and the velocity of each point increases with the increase of the strain, but the measuring point increases the wave velocity when the load is applied;When the specimen surface cracks, expect the waveform of measuring point 4# and 5# change in irregularities, the measuring point 2# waveform also changes irregularly and measuring point of the wave velocity has decreased;At the crack propagation stage, ultrasonic wave also changes irregularly along with the expansion of crack, wave velocity with the increase of the strain is also obvious downward trend;When the crack penetrates the whole specimen, the waveform of each measuring point changes abnormally, the continuity is bad, the waveform is irregular and the measured wave velocity is low.
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