中文摘要：

相近直径的锯齿型和扶手椅型碳纳米管可以共轴组合形成5—7碳环交替出现的柱形对称异质结.本文利用分子动力学方法研究了直径相近且等长锯齿型和扶手椅型碳纳米管形成的（n,n）-（2n,0）结在扭转过程中的扭矩和轴向应力随扭转角度的变化规律以及应力传递过程.研究发现,（n,n）-（2n,0）结扭转应变在达弹性限度内不会产生轴向应力,该效应对基于碳纳米管扭转特性的纳米振荡器件的设计具有重要意义.

英文摘要：

A coaxial cylindrical heterojunction of carbon tubes, which consists of alternant bands of 5- and 7-membered rings, can be formed by one armchair （n, n） carbon nanotube and one zigzag （2n, 0） carbon nanotube. The torsional mechanical properties of this kind of （n, n）-（2n, 0） heterojunction constructed by the same length of armchair and zigzag nanotubes are studied by using molecular dynamics method. In order to make a comparison, the relations of the torque and axial stress to torsional angle of （n, n） and （2n, 0） carbon tubes are also systemically calculated. Moreover, the transfer process of torsional stress in the （n, n）-（2n, 0） heterojunction is analyzed. Some important conclusions are obtained. Firstly, the torsional angle corresponding to the buckling point of carbon nanotubes is closely related to their torsional stiffness. The buckling angle decreases monotonically with torsional stiffness. Secondly, as the torsion develops, the torsional stre~s appears from the joint position due to the fact that the junction part in the （n, n）-（2n~ 0） heterojunction has the smallest torsional stiffness and then transfers from the joint position to both ends. The propagation velocity of the torsional stress in （n, n） nanotube which has smaller stiffness is faster than that in （2n, 0） nanotube with bigger stiffness. Finally, for the process of torsion within the elastic limit, no axial stress is produced in （n, n）-（2n, 0） heterojunction during the torsion. This effect is of great significance for designing the carbon nanotube-based nano-oscillator devices.