对圆形、方形截面形状的单晶Cu纳米杆拉伸变形过程进行了分子动力学模拟. 通过中心对称参数方法并结合位错形核理论分析了截面形状、截面面积和长细比对纳米杆拉伸力学特性的影响, 研究了单晶Cu纳米杆拉伸力学特性的尺寸依赖性. 结果表明: 首次屈服后, 纳米杆在“位错形核-位错延伸与滑移-晶格原子交叉滑移”的交替循环作用机制下, 产生塑性变形; 截面形状对纳米杆拉伸变形的初始塑性影响较小, 而对纳米杆拉伸力学特性的影响较大; 随着截面面积的增大, 两种截面形状的纳米杆都出现首次屈服点提前,屈服应力减小和弹性模量增大的现象; 与方形截面形状纳米杆相比, 圆形截面形状纳米杆的屈服应力的变化率较小, 其弹性模量的变化率较大; 当截面面积增大到500 nm2后, 两种截面形状纳米杆的弹性模量趋于稳定, 其值接近理论值84 GPa. 加大仿真规模后, 长细比对纳米杆的拉伸力学特性略有影响.
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 revealed. 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’modulus increases. Compared with that of the square cross–sectional nano–rod, the variable rate of yield stess of the circular cross-sectional nano–rod is smaller while the variable rate of young’s modulus is lager. 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 the nano–rods has a slight effect on the tensile mechanical properties when the simulation size increased.
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