冲击荷载下Ⅰ型裂纹与圆孔缺陷相互作用

采用数字激光动态焦散线和超动态应变测试系统,对含圆孔缺陷的有机玻璃板三点弯曲梁进行冲击断裂实验,开展Ⅰ型扩展裂纹与不同直径圆孔缺陷相互作用实验研究。结果表明：冲击载荷下预制裂缝尖端焦散斑不断增大,圆孔缺陷左、右边缘应变片测点表现出竖直受压、水平受拉的应力状态。裂纹起裂后沿直线扩展,主要表现为Ⅰ型断裂。初始裂纹扩展速度和动态应力强度因子大小相似,变化趋势相近,应变片测点水平和竖直方向均表现出拉应力状态。初始裂纹与圆孔缺陷贯通时止裂,贯通瞬间应变片测点的水平和竖直拉应力均达最大值。随着圆孔缺陷直径增大,次生裂纹起裂速度和起裂韧度均变大,起裂难度增高。研究结果为揭示动荷载下含缺陷岩石断裂机理提供借鉴。

Study on the Interaction between Type-I Crack and Circle Hole Defect under Impact Loading

The digital laser dynamic caustics and ultra-dynamic strain test system were used to conduct impact fracture experiments on three-point bending beams of polymethyl methacrylate specimen with circle hole defects. The interaction characteristics of type-I propagating crack and different diameter circular hole defects were studied. The experiment results show that the caustics spot continued to increase under impact loading. The left and right edges of the circle hole defect, strain gauge tested points, are in the stress state of vertical compression and horizontal tension. After the crack starts to initiate, it propagates in a straight line, mainly grows as type-I mode. The initial crack propagating velocity and the dynamic stress intensity factor are similar in magnitude, and the change trend is similar. Both the horizontal and vertical directions of the strain gage tested points show tensile stress state. When the initial crack and the circle hole defect coalesce, the crack arrests. Meanwhile the horizontal and vertical tensile stresses of the strain gauge tested points reach the maximum value. The bigger the diameter of the circle hole defect increases, the larger the secondary crack propagating velocity and the initiation toughness become. It is more difficult for the secondary crack to initiate. The research results provide a reference for revealing the fracture mechanism of rock with defects under dynamic loading.