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石英玻璃杆Taylor撞击实验的数值模拟

NUMERICAL SIMULATIONS OF TAYLOR IMPACT EXPERIMENTS OF QUARTZ GLASS BARS

  • 摘要: 采用离散元方法模拟石英玻璃杆Taylor撞击问题,再现了其破坏过程:在撞击端,杆以压缩失效波的形式破坏;在自由端,出现了密集的拉伸层裂破坏. 分析表明:层裂是失效波阵面应力快速下降引起的追赶卸载波,与弹性压缩前驱波在自由端反射引起的迎面卸载波相互作用的结果;随着撞击速度的增大,撞击端失效波造成的压缩破坏区域损伤程度增大,反射端层裂破坏损伤区域减小. 进一步对失效波阵面的结构变化及其波速问题进行了研究,发现失效区域随着扩张变成一段裂纹逐渐由密到稀的区段,将此区段分为高损伤区和低损伤区,研究发现由稀疏微裂纹组成的低损伤区的前端面传播速度和弹性前驱波速基本相同,为固定值;而高损伤区前端面的裂纹密度随着传播距离的增加变稀,直至过渡为低损伤区,其传播具有显著的速度衰减、端面模糊直至停止的过程. 高损伤前端面的平均速度随着撞击速度的增大而增大,并逐渐趋近于弹性波速. 最后与已有实验做了对比,发现实验中高速摄影观察到的玻璃中"失效波"阵面实际上是高损伤前端面,而稀疏的低损伤微裂纹很难捕捉.

     

    Abstract: The Taylor impact experiments of quartz glass bar were simulated by using a discrete element method (DEM) approach. The simulations provided detailed failure process of the glass bar: at the impact end, the bar failed in the form of compressive failure wave; at the free end, dense tensile spallation failure occurs. The analysis showed that the spallation is the result of the interaction between the chasing unloading waves caused by the rapid decrease of stress in the failure wave front, and the incoming unloading wave caused by the reflection of the elastic compression wave front at the free end. With the impact velocity increasing, the size of the compressive failure zone increases at the impact end, and the spallation failure zone decreases at the free end. Furthermore, the structural fronts and their propagation velocity of the compressive failure zone were investigated. It was found that the "failure front" in fact was a transition zone from dense crack region (the high damage region, HDZ) to sparse crack region (the low damage zone, LDZ). It was found that the propagation velocity LDZ front is basically the same as the elastic wave velocity, which is a constant. However, the HDZ front velocity decreases as it propagates. The average velocity of the HDZ front increases with the increasing of the impact velocity, and may approach the limit value of elastic wave velocity. In experiments, people usually reports the high-speed video observations of "failure waves" in glass bar after impact, which are actually the front of the HDZ, as the dense cracks formed the HDZ reflect lights to make the region bright and observable.

     

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