预扭转单晶铜棒拉伸行为的分子动力学模拟

Tensile Behavior of Pre-torsional Single Crystal Copper Nanorods:a Molecular Dynamics Simulation

一维纳米材料具备与宏观材料不同的力学性能,在微纳米器件中拥有开阔的应用前景.采用分子动力学方法研究了预扭转角度、纳米棒长径比、拉伸应变率对预扭转单晶铜棒拉伸行为的影响.结果表明:在较高应变率下,预扭转变形会导致轴向<100>取向单晶铜纳米棒拉伸流动应力提高,通过对位错结构演化过程分析发现,流动应力的提高是由于预扭转变形产生的位错网以及大角度晶界在拉伸时新形核的位错对拉伸过程中位错运动的阻碍作用;随着预扭转角的增大,初始位错先增多后减少并逐渐转变为大角度晶界,因此在随后拉伸加载过程中流动应力先增大后减小;由于初始位错网会缓解纳米棒拉伸过程中的局部应力集中,预扭转对拉伸流动应力的提升效果随纳米棒长径比的增大而增强.而在较低应变率下,预扭转产生的位错缓解了位错饥饿现象,使纳米棒的流动应力相比高应变率情形下有所降低.通过系统地研究单晶铜纳米棒预扭转再拉伸行为,有望为理解纳米棒在复杂载荷下的塑性变形机理提供理论支撑.

One-dimensional nanomaterials have different mechanical properties from macroscopic materials,and have broad application prospects in micro-nano devices.The effects of pre-torsion degree,aspect ratio of nanorods and tensile strain rate on the tensile behavior of pre-torsional single crystal copper nanorods were studied using the molecular dynamics method.The simulation results show that,at higher tensile strain rates,pre-torsional deformation leads to the increase of tensile flow stress of the axially<T00l>oriented single crystal copper nanorods.By analyzing the evolution process of dislocation structure,it is found that the initial dislocation network generated by pre-torsional deformation and the newly nucleated dislocations at large grain boundaries at the initial stage of stretching obstruct the dislocation movement during the tensile process,resulting in the increase of tensile flow stress.With the increase of the pre-torsion degree,the initial dislocations first increase,and then decrease and gradually change to the large-angle grain boundary,and the hindering effect of dislocation movement in the subsequent tensile process changes accordingly,so the average plastic tensile flow stress first increases and then decreases.The local stress concentration of nanorods with large aspect ratio is more serious during axial tension,and the initial dislocation network relieves the local stress concentration during the stretching process of the nanorods,so the enhancement effect of pre-torsional deformation on the tensile flow stress increases with the increase of the aspect ratio of nanorods.At lower tensile strain rates,the dislocations produced by pre-torsional deformation alleviate dislocation starvation,decreasing the tensile flow stress of the nanorods compared with that at a higher tensile strain rate.The tensile behavior of pre-torsional single crystal copper nanorods has been systematically studied,which is expected to provide theoretical support for understanding the plastic deformation mechanism of nanorods under complex loading.