冲击倾向性对煤体动态断裂行为的影响研究

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

为了探明冲击倾向性对煤体动态断裂特性的影响,对3类煤体进行了变上限循环加卸载试验及动静态I型动态断裂试验。结果表明:3类煤体变应力上限循环加卸载过程中的应变能U^(n)_(e)与输入能U^(n)_(in)之间存在近似线性函数关系,其统一表达公式为U^(n)_(e)=1.032U^(n)_(in)−5.536;同时测定以上3类煤体剩余弹性能指数C_(EF)分别为25.35、30.34、33.26 kJ/m^(3);通过单边缺口梁三点弯曲试验测得的以上3类煤体静态I型断裂韧度值K_(IC)值分别为0.249、0.291、0.347 MPa·m^(1/2),同时测得的冲击载荷作用下动态K_(IC)分别为0.344、0.416、0.527 MPa·m^(1/2),随着C_(EF)的增加,煤体动态K_(IC)增长倍数逐渐增大,表明煤体冲击倾向性将直接影响其动态断裂力学响应,煤体冲击倾向性越大,其动态断裂参数提高越多;此外,随着煤体冲击倾向程度的增加,动载荷作用后煤体破碎分形维数随之增大,表明煤体受冲击后断裂崩解的更加复杂破碎,动态断裂响应变得更加显著。

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 U^(n)_(e) and input energy U^(n)_(in) in the cyclic loading and unloading process of three types of coal,and the unified expression formula is U^(n)_(e)=1.032U^(n)_(in)−5.536;the residual elastic energy index C_(EF) of the above three types of coal is 25.35,30.34 and 33.26 kJ/m^(3),respectively.The K_(IC) 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•m^(1/2) through the three-point bending test of the single-side notched beam,and the dynamic K_(IC) values under the impact load are respectively 0.344,0.416,0.527 MPa•m^(1/2).With the increase of C_(EF),the growth ratio of coal dynamic K_(IC) 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.