On elastic properties of single-walled carbon nanotubes as composite reinforcing fillers

As one of the fundamental prerequisites for composite material applications of single-walled carbon nanotubes, their mechanical properties as reinforcing fillers should be identified in the conventional manner of mechanics of composite materials. In particular, identification of elastic properties under axial tension and compression, i.e., initial Young's modulus and Poisson's ratio in terms of longitudinal straining will have a considerable influence on the estimation accuracy of the mechanical (including elastic) properties of carbon nanotube reinforced composites. In this article, elastic properties of unchiral (arm-chair and zig-zag) single-walled carbon nanotubes of different diameters under infinitesimal, small but finite, and large strain regions are numerically computed based on the definition of tube cross-sectional area which will be adopted in the composite materials communities. A classical molecular dynamics simulation using the well-verified Tersoff-type empirical potential for carbon and hydrocarbon molecules is employed. Contrary to what has been reported so far for the case of infinitesimal straining which has been conducted in this study as well, it has been shown that the elastic properties such as initial Young's modulus and Poisson's ratio of the nanotubes in a small but finite strain range should be more or less treated as chirality-dependent, diameter-dependent, and bi-modal ones. The Mooney-Rivlin constants of unchiral carbon nanotubes are also evaluated. From the present results, it is cautioned that the carbon nanotubes are not always stiff and strong when they are looked upon as reinforcing fibers or fillers of composite materials.