Study On Mechanical Coupling Effect Caused By Carbon Nanotubes Reversed

In recent years, carbon nanotubes have gained extensive investigations due to their attractive mechanical and electrical properties, which make them the most promising candidates for building blocks of nano-electro-mechanical systems (NEMS). The idea of building torsional parametric oscillators tuned by axial pre-stress or electrostatic force has also been proposed. In these applications, the torsional mechanical behaviors of carbon nanotubes are essentially important for NEMS.In this paper, we carried out a simulation of the single-walled and double-walled carbon nanotubes using classical molecular dynamics method, to study the torsional molecular dynamics of them. Made some meaningful results, those are:(1) Different diameter carbon nanotubes’torque have the same trend with torsion angle and shear strain.In the torsional beginning (mean small shear strain),the torque increases linearly with respect to torsional angle and shear strain. Smaller diameter carbon nanotubes, the torsion torque required monotonically decreasing, indicating the torsional stiffness amsller of small carbon nanotubes, but have greater shear strain limit of the elastic deformation.(2) Carbon nanotubes have their own buckling point, beyond which when the torsional angle goes, a structural phase transition happens, and the slope of the curve and torsional stiffness of the carbon nanotubes will both reduce(3) The relationship between torsional torque and torsional angle during the buckling deformation, in the zigzag and armchair nanotubes, shows an obvious difference, indicating that the structure of tubes plays an important role in their mechanical behaviors. This phenomenon could act as an effective means of detecting the chirality of carbon nanotubes.(4) The direction of the axial stress in torsion is also determined by the structure of carbon nanotubes. Armchair nanotubes have negative axial stress which exhibits a trend of tube contraction, while the zigzag nanotubes have positive axial stress with a trend of extending the tube.(5) When the length of nanotube with a negative axial stress (such as the zigzag nanotubes) goes beyond a certain value, the stress will release by bending, causing the increment of diameter and the extension of the length. This could be applied in the designing of functional devices. The tube which has negative axial stress(such as the armchair carbon nanotubes) can’t bend during twisting. (6) There is bending or not in double-wall carbon nanotubes (DWCNT) completely depends on the axial stress-response characteristics of the outer tube, and independent with the inner wall. If the outer wall has a negative axial stress, the DWCNT will show the bending deformation induced by the torsion applied. Compared with the single-walled tubes, the torsion-induced bending of DWCNT could happen at a shorter length. This decrement of critical length of bending causes by the axial stress of the inner tube. Even with different direction of the axial stress on the inner tube, the result whether there is bending or not on the DWCNT will not change.Hopefully my results could provide a beneficial reference to the design and preparation of nano-scale functional devices based on carbon nanotubes.