界面裂纹萌生与扩展的分子动力学模拟

运用分子动力学模拟方法研究了裂纹在界面端处萌生与沿界面扩展的临界条件. 模拟考虑了一双相材料的3种模型，即构成90°/90°和 90°/180°夹角的两个界面端和一个界面裂纹. 模拟采用了包含原子区域与连续区域的并发型多尺度模型，即在界面端尖端和裂纹尖端附近 采用分子动力学(MD)方法，MD区域之外则按照线弹性有限元方法分析. 结果表明，在断裂启动时刻，3个模型沿界面的最大应力均达到界面理想强度；而且，其界 面能恰好足以克服界面材料的本征内聚能. 因此，界面端裂纹萌生与沿界面扩展的断裂条件可以通过界面理想强度和内聚能联系起来. 并基于模拟计算结果提出了界面断裂启动的统一准则.

MOLECULAR DYNAMICS SIMULATIONS OF INTERFACIAL CRACK NUCLEATION AND PROPAGATION

Molecular dynamics(MD)simulations are carried out to study the critical conditions for crack nucleation at the interface edges and for crack propagation along the interface,and their relations.MD method is employed to examine the fracture behaviors near the apexes of the interface edges and near the tip of the interface crack,with the outer boundaries of the simulation cells being constrained by the elastic finite element displacement fields.The simulation results show that,at the instant of fracture initiation,the maximum stresses along the interfaces reach the ideal strength of the interface;also their interface energies can just overcome the intrinsic cohesive energy of the interface material.Therefore,the fracture conditions for crack nucleation at the interface edges and for crack propagation along the interface could be correlated through either the ideal strength or the cohesive energy of the interface.Further,a unified criterion for interface fracture initiation is proposed based on the simulation results.