纳米镍板裂纹扩展的分子动力学模拟和宏微观分析

Continuum analysis and molecular dynamics simulation of crack initiation in nano nickel slab

建立了半无限弹性纳米镍板Ⅰ型裂纹扩展的二维分子动力学计算模型。采用镶嵌原子法描述原子间作用,模拟了纳观裂纹区在远场常应变率作用下变化直至起始扩展的过程。同时基于原子势函数和二维正三角形晶格常数计算材料弹性参数,进行连续介质力学断裂分析。分子动力学模拟和宏微观分析均得到裂纹起始扩展的临界时刻、裂尖应力场和原子平均能量。二者的结果比较表明本文的二维简化模型和模拟方法可以准确地描述Ⅰ型裂纹扩展的物理本质,基于原子势函数和晶格常数的连续介质力学分析也是一种可行的研究纳米材料断裂的方法。

Mode Ⅰ crack initiation in a nano-scale elastic seml-infinite nickel slap conslsung of two-dimensional triangular lattices was studied by both molecular dynamics simulation and continuum analysis based on Griffith fracture criterion. The inter-atomic potential in molecular dynamics simulation was described by Embedded Atom Method （EAM） and the elastic constants in continuum analysis were deduced from inter-atomic potential and crystal lattices. Molecular dynamics simulation shows that the reduced plane model and numerical method in this paper can not only reveal the movement of atoms near the crack clearly but also give the critical time of crack initiation accurately as the continuum fracture analysis does. When crack starts to grow, the normal stress and average atom energy at the crack tip in atomistic simulation agree well with the results of continuum analysis. Continuum analysis with material property parameters determined by inter-atomic potential is proved to be another promising way for solving failure problem on nano scale.