ABSTRACT
Carbon nanotubes (CNTs) are macromolecules of carbon in a periodic hexagonal arrangement with a cylindrical shell shape [1]. They can be viewed as one (or more) graphite sheet(s) rolled into a seamless tube. A pair of indices (n,m), called the chirality, is used to represent the way a graphite sheet is wrapped. When m = 0, the nanotubes are called “zigzag,” and when n = m, they are called “armchair.” It is widely acknowledged that a reasonable and accurate estimate of their material properties, such as Young’s modulus, shear strength, Poisson’s ratio, and bending rigidity, is critical for the potential applications of the material [2]. Experimental investigations of the material properties of CNTs have been explored intensively. Krishnan et al. [3] estimated the Young’s modulus of single-walled carbon nanotubes (SWNTs) to be 0.9 TPa-1.7 TPa by observing their freestanding room-temperature vibrations in a transmission electron microscope. Salvetat et al. [4] used an atomic force microscope and a special substrate to estimate the elastic and shear moduli of a SWNT to be of the order of 1 TPa and 1 GPa, respectively. Besides the research žndings on SWNTs, Poncharal et al. [5] observed the static deformation of a multiwalled CNT (MWNT) and indicated that the Young’s modulus of the materials is about 1 TPa using a transmission electron microscope. Wong et al. [2] experimentally determined
22.1 Introduction .................................................................................................. 363 22.2 Elastic Rod Theory on Material Properties of DWNTs ...............................364 22.3 Molecular Simulations via Materials Studio ................................................ 365 22.4 Conclusions ................................................................................................... 369 Acknowledgments .................................................................................................. 369 References .............................................................................................................. 370
the Young’s modulus of individual, structurally isolated silicon carbide nanorods and MWNTs that were pinned at one end to molybdenum disulžde surfaces and found the value to be 0.7 TPa-1.9 TPa. In addition to these experimental endeavors, the mechanical properties of CNTs in closed forms have also been explored. A stick-spiral model [6] was developed to investigate the mechanical behavior of SWNTs, especially the estimate of Young’s modulus and shear modulus based on a molecular mechanics concept. Other close-form expressions for mechanical properties of achiral CNTs were attempted via a concept of representative volume element of the chemical structure of a graphite sheet [7-8]. Length-dependent in-plane stiffness and shear modulus of chiral and achiral SWNTs subjected to axial compression and torsion have recently been discovered [9]. The strain energy of the tubes measured from the molecular mechanics and the corresponding calculated second derivative of the energy were used for the estimation of the properties of CNTs based on an elastic rod theory in relating the CNT material properties directly to the molecular mechanics calculations.
