单晶Cu纳米杆拉伸力学特性的尺寸依赖性模拟

来源期刊：金属学报2010年第10期

论文作者：白清顺 童振 梁迎春 陈家轩 王治国

文章页码：1173 - 1180

关键词：分子动力学； 拉伸； 纳米杆； 位错形核； 力学特性

Key words：molecular dynamics； tension； nano-rod； dislocation nucleation； mechanical property

摘    要：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500nm²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84GPa.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.

Abstract: 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 the nano-rods has a slight effect on the tensile mechanical properties when the simulation size increased.