| Summary: | 碩士 === 國立交通大學 === 機械工程系所 === 97 === This study aims to investigate the mechanical properties of graphene and single/multi-walled carbon nanotubes(S/MWCNT) by analytical molecular structural mechanics and molecular dynamics (MD). The interatomic covalent bond of carbon-carbon is represented by AMBER force field which was employed in the analytical molecular mechanics and MD simulations as well, and the non-bonded interaction was described by Lennard-Jones potential. In particular, in-plane elastic properties of MD graphene model obtained from applying stress or strain were compared with analytical solutions. Results indicated that in-plane properties, predicted by analytical solution demonstrate a good agreement with MD solution. It was found that in-plane properties of graphene basically satisfied the relation, , and thus it can be regarded as a transverse isotropic material. Applying stress on the graphene model in the out-of-plane direction and calculating the relative displacement between graphene layers interacted by van der Waals potential, out-of-plane shear modulus could be derived.
Because of the weak Lennard-Jones potential, the in-plane mechanical properties are higher than out-of-plane shear modulus. Since van der Waals potential may affect the mechanical properties of the graphene model, the effect of van der Waals on graphene mechanical properties was also investigated in the study.
The axial Young’s modulus and Poisson ratio of S/DWCNTs is predicted by the MD method. In this article, elastic properties of unchiral (zigzag and armchair) S/DWCNTs of different diameters are studied and discussed. The results indicated that Young’s modulus of CNTs varies with the tube diameter and is affected by their helicity. With increasing the tube diameter, the Young’s modulus of both armchair and zigzag CNTs increases. The Young’s modulus of zigzag CNTs is lower than that of armchair at smaller diameters, however, at larger diameters there is no significant difference observed between armchair and Zigzag CNTs.
The interlayer atomistic force of between the neighboring graphene layers in DWCNTs was examined by performing inner tube pullout and rotation tests with respective to the outer tube at stationary position. The pullout force corresponding to the pullout distance was measured in the pullout test and the torque of inner tube and interlayer VDW energy variation associated with the rotation angle was calculated in the rotational tests. This information is very essential for understanding the load transfer efficiency between the graphene layers in DWCNTs when they was considered an reinforcement in the nanocomposites.
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