半圆盘构件冲击断裂特性的动态焦散线实验研究

采用动态焦散线实验系统，对有机玻璃（PMMA）在冲击载荷下的I型和I-II混合型裂纹在起裂和扩展时的动态断裂特性进行了研究。结果表明：随着PMMA由I型断裂转变为I-II混合型断裂，从落锤作用在试件上到裂纹起裂所需时间不断增加，说明裂纹起裂需要的能量有所增加，同时从裂纹起裂到最终贯通所需时间不断减少，说明裂纹平均扩展速度也不断增大；在I型断裂中，PMMA的断裂韧度KIC为2.04 MN/m3/2，而在I-II混合型断裂中，PMMA的断裂韧度KIC低于I型断裂时的断裂韧度KIC，但是KIIC有所增大；对于I-II混合型断裂，PMMA极限扩展速度约为366m/s，当达到极限扩展速度后，裂纹尖端出现微裂纹增韧现象，使裂纹的表面能迅速增大，随后裂纹的扩展速度迅速减小。

Dynamic Caustics Experiments with Semi-Circular Specimen under Impact loading

The initiation and propagation of mode I and mixed mode I-II crack in Polymethylmethacrylate (PMMA) subjected to impact loading was studied by using dynamic caustics experimental system. It was shown that the initiation needed more energy from pure mode I to mixed mode I-II for PMMA, because the time-interval before crack initiation increased. The time-interval decreased from crack initiation to crack arrest, and it indicated that the average propagation velocity increased. Fracture toughness KIC of PMMA was 2.04 MN/m3/2 for mode I fracture. For mixed mode I-II fracture, the fracture toughness KIC was lower than one of mode I fracture, but the fracture toughness KIIC was higher. For mixed mode I-II fracture, the maximum propagation velocity PMMA was about 366m / s, then micro-cracks toughening phenomenon appeared at the crack tip. The surface energy of crack increased, and its propagation velocity decreased rapidly.