Crack propagation law of mode Ⅰ dynamic fracture of coal：Experiment and numerical simulation

In order to study the influence of impact speed,bedding angle and notch length on the speed and path of crack propagation of model Ⅰ dynamic fracturing of coal,the split Hopkinson pressure bar test and numerical simulation based on continuum-discontinuum element method are carried out.The notched semi-circular bending specimens with different bedding angles and three notch lengths are impacted under various loading rates.The whole fracturing process from the initiation,the propagation to the failure of the specimen is monitored.The simulation results also agree well with the test results.It is proved that the CDEM numerical simulation method can better simulate the progressive failure process of coal from continuous to discontinuous.The experimental results indicate that the instantaneous crack propagation speed of coal specimen fluctuates greatly,and the crack propagation is fast at the early stage and slow at the later stage.The crack propagation of the specimen can be divided into a high-speed expansion phase and a steady-speed expansion phase.The impact speed has the greatest influence on the average crack propagation speed,the second is the notch length,and the least is the bedding angle.The crack propagation speed increases with the increase of impact speed,and the growth gradually becomes gentle,and decreases with the increase of notch length.If the influence of the bedding angle is ignored,the two-factor prediction model of the impact speed and notch length on the average crack propagation speed can be obtained.It is found that the greater the impact speed,the shorter the crack initiation time.But the impact speed has little effect on the crack propagation path.The bedding angle has a greater effect on the crack propagation path.Moreover,the crack propagation path is more curved due to the crack expansion along the beddings when the bedding angle is 22.5°,45.0° and 67.5°.