纳米铜单晶拉伸力学性能的分子动力学模拟

采用分子动力学模拟了绝对零度时三种不同边界条件下纳米铜单晶的拉伸力学性能。计算结果发现：不同边界约束对钢单晶的内在原子运动和整体力学行为有明显影响；纳米杆、纳米薄膜良好的延性主要来源于位错运动；铜单晶块体的破坏源于内部孔洞的发展，破坏时延性较差；此外，纳米杆、纳米薄膜存在较大的表面张力。

Molecular Dynamics Simulation of Tensile Mechanical Properties of Nano-single Crystal Copper

In order to understand the elastic and plastic def or mation mechanism of nano components, computer simulations are carried out on the tensile properties of nano single crystal copper under three different boundar y conditions at zero temperature by embedded atom method(EAM) and molecular dyna mics. The numerical atomic models of crystal copper under three periodic boundar y conditions correspond respectively to nanowire(four free surfaces), nanofilm(t wo free surfaces) and bulk(no free surface). These atomic models are strained st epwise along the [001] direction. Snapshots of atomic models at different stra in stages are given. It is found that different boundary conditions lead to diff erent mechanical behaviors. The stress strain curve of nanowire resembles that o f nanofilm, except that nanofilm has a little higher yielding and flow stress. B oth nanowire and nanofilm exhibit excellent plasticity, which comes from the cry stallographic slips on the (111) plane. The dislocation in nanowire with four free surfaces has more freedom to move, while less dislocation movement appears in nanofilm with two free surfaces leading to an enhancement in the yielding st rength. From snapshots of nanowire and nanofilm, stacking fault and atomic step on the surface can be seen clearly. The stress strain curve of the bulk has a q uite different appearance from that of nanowire or nanofilm. Bulk has a very high yielding stress and its stress strain curve drops twice: the first drop is succeeded by a little stress increase, and the second stress drop causes a mono tonous decline to zero. As bulk has no free surface, dislocation is prohibited ultimately, which results in a different stress strain curve. From the atomic p ictures, no dislocation except some distortion can be found after the first stre ss drop, and after the second drop, micro holes can be seen in the bulk. As stra in increases, the holes evolve and eventually cause the break. The simulation res ults also show that there is significant surface tension on the free surfaces of nanowire and nanofilm.