冲击荷载下对称裂纹动态扩展规律研究

Study on Dynamic Propagation Law of Symmetrical Crack Under Impact Load

为研究冲击荷载下岩石等脆性材料中对称裂纹的断裂机理,利用数字激光动焦散试验系统,对含不同倾角对称初始裂纹有机玻璃板试件进行了冲击试验,研究了裂纹倾角对对称裂纹动态断裂力学行为的影响,并利用有限元程序ABAQUS对试验进行了模拟。试验研究结果表明:裂纹扩展轨迹受试件中初始裂纹倾角的影响,初始裂纹倾角为60°和90°时,裂纹扩展表现为相互排斥,初始裂纹倾角为120°和150°时,裂纹在扩展过程中逐渐汇聚;Ⅰ型应力强度因子的变化规律受初始裂纹倾角的影响,裂纹起裂时刻的应力强度因子随初始裂纹倾角的增大而减小;初始裂纹倾角会影响裂纹尖端应变能累积和释放的快慢,当初始裂纹倾角为90°时,起裂难度最小,裂尖应变能释放较为平缓;当初始裂纹倾角为锐角和钝角时,起裂难度加大,应变能释放都较为迅速。数值模拟研究表明:初始裂纹对称轴上的最大主应力与裂纹尖端到该点的距离呈负相关,模拟所得裂纹扩展路径与试验结果相符。

In order to study the fracture mechanism of symmetrical cracks in brittle materials such as rocks under impact load, the impact tests of PMMA specimens containing symmetric cracks with different inclination angles were carried out by digital laser dynamic caustics experimental system. The effect of crake inclination on the dynamic fracture behavior of symmetrical crack was studied, and the experiment was simulated by ABAQUS. The experimental results are concluded as follows. Firstly, the propagation path is affected by the initial crack inclination. When the initial crack inclination is 60° and 90°, the cracks propagation repel each other, and when the initial crack inclination is 120° and 150°, the cracks converge gradually during the propagation process. Secondly, the change law of mode I stress intensity factor is affected by the initial crack inclination. The stress intensity factor at the crack initiation time decreases with the increase of the initial crack inclination. Thirdly, the initial crack inclination will affect the speed of strain energy accumulation and release at the crack tip. When the initial crack inclination is 90°, the difficulty of crack initiation is the smallest, and the release of strain energy at the crack tip is relatively gentle. Finally, when the initial crack inclination is acute and obtuse, the crack initiation becomes more difficult and the strain energy is released more rapidly. The numerical simulation results show that the maximum principal stress on the symmetry axis of the initial crack is negatively correlated with the distance from the crack tip to the point, and the simulated crack propagation path is consistent with the experimental results.