Simulation of scale dependency on tensile mechanical properties of single crystal copper nano-rod

The tension process of single crystal Cu nano-rods with different cross section shapes were simulated by molecular dynamics at atomic scale. Based on centrosymmetry parameter method and combined with the dislocation nucleation theory, the effect of cross-section shape, cross-sectional area and slenderness ratio on the tensile mechanical properties of the nano-rods were analyzed, and the scale dependency of tensile mechanical properties of the single crystal Cu nano-rods has been studied. The results show that after first yield, the nano-rods produce plastic deformation under the "dislocation nucleation-extended dislocation and sliding-lattice atom cross-slip" mechanism of the alternating cycle. The geometry of cross-section has negligible effects on the tensile initial plasticity of the nano-rods, while it shows apparent effects on the tensile mechanical properties. With the increase of cross-sectional area, two types of nano-rods have the phenomenon of early yield point, yield strength decreases and Young's modulus increases. Compared with that of the square cross-sectional nano-rod, the variable rate of yield stress of the circular cross-sectional nano-rod is smaller and the variable rate of Young's modulus is larger. As the cross-sectional area increases to 500 nm², the Young's modulus of the two types of nano-rods become stable, and is close to the theoretical value of 84 GPa. Moreover, the slenderness ratio of he nano-rods has a slight effect on the tensile mechanical properties when the simulation size increased.