基于离散元法分析增韧陶瓷圆环的动态膨胀碎裂

为研究高强度高脆性陶瓷的冲击拉伸断（碎）裂问题，开展了材料动态膨胀碎裂数值模拟研究。基于离散元方法，应用平节理接触模型分析高应变率下增韧陶瓷圆环的自由膨胀运动，获得了圆环膨胀碎裂过程中颗粒运动速度和系统能量的变化规律。结果表明：圆环断裂之前，以中层颗粒为基准，内层颗粒的径向速度呈现出增大的跳动，外层颗粒的径向速度显示出减小的跳动，这种跳动与陶瓷圆环的刚性有关，与初始加载速度无关；圆环断裂时刻，圆环内产生卸载波，同时伴随着应变能释放，导致圆环内层颗粒出现径向速度减小的跳动，外层颗粒径向速度则出现速度增大的跳动，这种速度跳跃现象将有助于实验中确定圆环的初始脆性断裂时刻；陶瓷圆环碎片的平均尺寸随应变率增加而减小，与文献［17-18］理论模型结果吻合较好。

Dynamic Expansion and Fragmentation of Toughened Ceramic Ring Based on Discrete Element Method

The dynamic expansion fragmentation of ceramic is numerically simulated to study the impact tensile fracture of ceramic with high strength and brittleness. The free expansion motion of toughened ceramic ring at high strain rate is studied using flat-joint contact model based on the discrete element method, from which the variation laws of particle motion velocity and system energy during the expansion and fragmentation process of ring are obtained. The results show that, before the ring fracture, the radial velocity of inner particles presents an increasing jump in the middle layer, while the radial velocity of outer particles presents a decreasing jump. The velocity jump is related to the rigidity of ceramic ring, but not to the initial loading velocity, at the moment of ring fracture, the release of strain energy is accompanied by the formation of unloading wave in the ring. Due to this fact, the radial velocity of outer particles presents an increasing jump, while the radial velocity of inner particles presents a decreasing jump. This velocity jump phenomenon is helpful to determine the initial brittle fracture time of the ring in the experiment; the normalized size of ceramic fragments decreases with the increase in normalized strain rate, which is in good agreement with the theoretical model in Ref.［17-18］.