Study on the influence of impact tendency on dynamic fracture behavior of coal

In order to investigate the influence of impact tendency on dynamic fracture characteristics of coal, cyclic loading and unloading tests with variable upper limit and dynamic and static type I dynamic fracture tests are carried out on three types of coal. The test results show that there is an approximate linear function relationship between strain energy Un e and input energy Un in in the cyclic loading and unloading process of three types of coal, and the unified expression formula is Un e =1.032Un in−5.536; the residual elastic energy index CEF of the above three types of coal is 25.35, 30.34 and 33.26 kJ/m3, respectively. The KIC values of the static type I fracture toughness of the above three types of coal mass are respectively 0.249, 0.291 and 0.347 MPa•m1/2 through the three-point bending test of the single-side notched beam, and the dynamic KIC values under the impact load are respectively 0.344, 0.416, 0.527 MPa•m1/2. With the increase of CEF, the growth ratio of coal dynamic KIC increases gradually, indicating that the impact tendency of coal will directly affect its dynamic fracture mechanical response. The greater the impact tendency of coal, the more the dynamic fracture parameters increase. In addition, with the increase of the impact tendency of coal, the fractal dimension of coal crushing under dynamic load increases, indicating that the fracture disintegration of coal under impact becomes more complex and the dynamic fracture response becomes more significant.