高应变率下延性金属中微孔洞贯通行为的数值分析

采用有限元分析方法，研究了延性金属材料动态拉伸断裂过程中微孔洞之间贯通行为，讨论了初始孔洞间韧带距离和加载应变速率的影响。通过实时跟踪测量微孔洞长大过程中的形状改变，定量判断微孔洞开始贯通时刻。计算结果显示微孔洞从独立长大向微孔洞贯通转变开始的临界韧带距离约为0.5倍微孔洞实时直径，其对初始微孔洞间韧带距离和加载应变速率不敏感。从物理机制上看，微孔洞间贯通行为是通过塑性应变场相互作用实现的，但孔洞间韧带区域的塑性应变场需要达到一个临界阈值才能驱动微孔洞开始贯通。在材料中微孔洞统计均匀分布的假定条件下，指出临界孔洞间韧带距离（ILD_c）判据和临界孔洞体积分数（f_c）判据在物理本质是一致的，可以相互转换。

Simulation of Viod Coalescence in Ductile Metals Under High Strain Rate

The void coalescence and interaction in dynamic tensile fracture of ductile metals were investigated by using axial symmetric finite element analysis. The influences of initial ligament distance between voids and loading strain rate on the void coalescence process were discussed. The start time of void coalescence was estimated quantitatively through correlated shape evolution of the voids. The measurement results show that the critical ligament distance at the start time of coalescence is approximately a half of void diameter, which is independent of initial separation distance between voids and strain rate. In reality, the voids may interact through their plastic fields. However, a critical plastic strain threshold in the ligament zones is needed to drive the void coalescence. Assuming that the voids are uniformly distributed within the damaged material, the critical ligament distance are consistent to the critical porosity in physical essence, and can be transformed each other.