单壁碳纳米管拉伸变形的原子尺度模拟

采用分子动力学方法对单壁碳纳米管的拉伸变形行为进行了模拟,结果表明,碳纳米管具有较高的断裂应变.在结构产生缺陷之前,碳纳米管表现出弹性变形的特征.通过对能量变化的分析可以看出,能量分布的不均匀是导致结构失稳产生缺陷的主要因素.通过对含初始结构缺陷的碳纳米管在拉伸变形过程中的构型变化进行分析,发现在缺陷附近原来相邻的两个六边形蜂窝结构,随着拉伸变形的发展转变成5 7结构(Stone Wales转变),能量产生突变,应变能的释放使系统能量降低.分析也表明,较少数目的初始缺陷对碳纳米管的力学性质并不会有太大影响.     

Orientation and Rate Dependence of Wave Propagation in Shocked Beta-SiC from Atomistic Simulations

The orientation dependence of planar wave propagation in beta-SiC is studied via the molecular dynamics （MD） method. Simulations are implemented under impact loadings in four main crystal directions, i.e., （lO0）, （llO）, 〈111〉, and 〈112}. The dispersion of stress states in different directions increases with rising impact velocity, which implies the anisotropic characteristic of shock wave propagation for beta-SiC materials. We also obtain the Hugoniot relations between the shock wave velocity and the impact velocity, and find that the shock velocity falls into a plateau above a threshold of impact velocity. The shock velocity of the plateaux is dependent on the shock directions, while 〈111} and 〈112/ can be regarded as equivalent directions as they almost reach the same plateau. A comparison between the atomic stress from MD and the stress from Rankine-Hugoniot jump conditions is also made, and it is found that they agree with each other very well.