Large-Scale Molecular Dynamics Simulation On Tension Mechanical Properties Of Single Crystal Copper Nano-ROD

The mechanical property of nano-structures is an important factor affecting its performance. In this paper, the tension process of the ideal and defective single-crystal copper nano-rod were simulated by the parallel molecular dynamics simulation technique, and the scale dependency of tension mechanical properties and the effects of hole defects on the tensile deformation of nano-rods were studied. This issue is of great theoretical and practical value on the comprehensive understanding of the deformation, failure mechanisms, the design and manufacture of nano-structures.Firstly, we built up the computing platform of parallel simulation for this subject based on LAMMPS software, and verify the efficiency, accuracy and scalability of parallel algorithms. By the simulation of ideal single-crystal copper nano-rod with different cross section shape, the effect of cross-section shape on the tensile deformation mechanisms and mechanical properties of nano-rod were analyzed. The results indicate that the geometry of cross section shows a little effect on the tensile initial plasticity of nano-rod, while shows large effect on the tensile mechanical properties.Secondly, the scale dependence on tensile mechanical properties of single-crystal copper nano-rod was studied by the simulation of multiple-scale nano-rod with different cross section shape. The results show that the geometry shape and size of cross section has large effect on the tensile mechanical properties of nano-rod, while the slenderness ratio shows a little effect. With the increase of cross-sectional area, both of two types of nano-rods have the phenomenon of early yield point, yield strength decrease and young's modulus increase. As the cross-sectional area increases to 500nm2, the young's modulus of the two types of nano-rods become stable, and its value goes close to the theoretical value of 84GPa.Finally,the model of single-crystal copper nano-rod with holes were built, based on centrosymmetry parameter method and combined with the dislocation nucleation theory, the effect of hole size, hole spacing, hole number and hole configuration on the tensile deformation mechanisms and mechanical properties of nano-rod were investigated. The results reveal that the strength of the material was significantly reduced by the existence of holes. Hole spacing and hole configuration have great effect on the process of the holes coalescence, and thus affect the mechanical properties of nano-rod. With the same hole volume, the greater the number of holes, the more ratio of dislocation nucleation. The overlap between dislocations prevented the further expansion of the dislocation and resulted in an increase of the young's modulus and yield strength of the nano-rod.