冲击载荷作用下圆孔缺陷对裂纹动态扩展行为的影响规律

空腔和裂纹缺陷通常共存于深部地下岩体中，它们共同影响着岩体的结构安全性与稳定性。为了探究动力扰动载荷下圆形空腔对裂隙岩体内裂纹扩展行为的影响规律，提出了不同圆孔倾角的直裂纹空腔圆弧开口试件（circular opening specimen with straight crack cavity, COSSCC），利用自制大型落锤冲击实验装置进行动态加载实验，同时采用裂纹扩展计系统测试了裂纹的动态起裂时刻与裂纹扩展速度等各种断裂力学参数，随后采用有限差分软件Autodyn进行裂纹扩展路径与圆孔周围应力场的数值分析，并采用有限元软件Abaqus计算裂纹的动态起裂韧度与裂纹扩展过程中的动态扩展韧度。结果表明:（1）当圆孔倾角θ小于10°时，裂纹扩展路径会偏折并穿过圆孔表面；当圆孔倾角θ为20°与30°时，裂纹扩展路径向圆孔方向发生偏折但不会穿过圆孔，圆孔具有明显的裂纹扩展引导作用； 当圆孔倾角θ为40°与50°时，裂纹扩展路径不会发生偏折，圆孔引导作用明显减弱。（2）当裂纹扩展路径达到圆孔空腔附近时，裂纹尖端的拉伸应力区与圆孔边缘的拉伸应力区发生重合，此时裂纹扩展速度显著增大，裂纹动态断裂韧度显著减小。（3）裂纹的偏折方向与裂纹尖端最大周向应力的方向基本一致。（4）裂纹动态断裂韧度始终小于裂纹起裂韧度，且裂纹动态断裂韧度与裂纹动态扩展速度呈负相关关系。裂纹动态扩展速度越大，裂纹动态断裂韧度越小。

Influence of circular hole defect on dynamic crack propagation behavior under impact loads

Cavities and crack defects usually coexist in deep earth rock mass structures, which together affect the structural safety and stability of rock masses. In order to study the effect of circular cavity on crack propagation behavior in rock mass under dynamic loads, circular opening specimens with straight crack cavity (COSSCC) specimen were proposed in this study, and a large-scale drop hammer impact device was applied to conduct impact tests. Crack propagation gauges were implemented to measure fracture mechanics parameters, such as dynamic crack initiation time and crack propagation velocity. Then a modified finite difference code Autodyn was applied to carry out the numerical simulation analysis of crack propagation path and stress field around the circular hole. The traditional finite element code Abaqus was also used to calculate the dynamic initiation toughness and dynamic propagation toughness. The results indicate that: (1) when the inclination θ of the circle hole is less than 10°, the crack propagation path deflects and passes through the surface of the circle hole; when the inclination θ of circle hole is 20° and 30°, the crack propagation paths deflects in the direction of the hole but does not pass through the circular hole, indicating that the circular hole has obvious guiding effect on crack propagation; when the inclination θ of circle hole is 40° and 50°, crack propagation path does not deflect, and the guiding effect of the circular hole is obvious weaken. (2) When the crack propagation path reaches the vicinity of the circular hole, the tensile stress zone at the crack tip coincides with the tensile stress zone at the edge of the circular hole. At this time, the crack propagation speed increases significantly, and the dynamic fracture toughness of the crack decreases significantly. (3) The deflection direction of the crack is basically the same as the direction of the maximum circumferential stress at the crack tip. (4) The dynamic fracture toughness of the crack is always smaller than the crack initiation toughness, and the dynamic fracture toughness of the crack has a linear relationship with the dynamic crack growth rate. The larger the dynamic crack growth rate, the smaller the dynamic fracture toughness of the crack.