Atomistic Study of Mechanical Properties of Carbon Nanotubes
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Atomistic Study of Mechanical Properties of Carbon Nanotubes T. Narita and K. Shintani Department of Mechanical Engineering and Intelligent Systems, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan, [email protected] ABSTRACT The mechanical properties of single-walled carbon nanotubes are investigated by means of molecular dynamics simulations. The Tersoff-Brenner potential is used for the calculation of the interatomic forces. Two kinds of simulation cells are considered; one adopts the periodic boundary condition along the tube axis and the other corresponds to tube clusters. The atoms at the ends of a simulation cell are translated along its axis, and the Young’s modulus and Poisson’s ratio are estimated. How these mechanical properties of carbon nanotubes depend on their chiralities is discussed. INTRODUCTION Carbon nanotubes are unique nanoscale structures discovered by Iijima [1], and have attracted much attention because of their electronic and mechanical properties. They are the cylindrical structures constructed by rolling graphene sheets. The construction is determined by the pair of integers (n,m) which specify the chiral vector. In addition to their applicability to nanodevices, carbon nanotubes are expected to be used to fabricate ultimate fibers due to their superior strength along their tube axes. Single-walled nanotubes (SWNTs) also show very large flexibility in the direction perpendicular to the tube axes. These remarkable mechanical properties stem from the strong intralayer sp2 bonds in graphene sheets [2]. As reviewed by Yakobson and Avouris [3] and by Harris [4], the mechanical properties such as the Young’s modulus and Poisson’s ratio of SWNTs and of multiwalled nanotubes (MWNTs) have been investigated by both experimental measurements and numerical simulations. Although the number of experimental evidences implying that SWNTs and MWNTs have extremely large Young’s moduli and tensile strengths is increasing, the determinations of these mechanical properties are still challenging tasks due to the technical difficulties in the manipulation of nanoscale materials. One of the promising ways to determine their Young’s moduli is that attempted by Krishnan et al. [5]. They observed the freestanding vibrations of SWNTs at room temperature in a transmission electron microscope, and correlated the amplitudes of their thermal vibrations with the Young’s modulus assuming that the vibration profile is that of a clamped cantilever. They estimated an average value of the Young’s modulus 1.25-0.35/+0.45TPa for SWNTs. Another way to determine the Young’s modulus of carbon nanotubes is that using the tip of an atomic force microscope. By using this tip an anchored carbon nanotube is bent while the force exerted by the tube is recorded as a function of the displacement. By this method, Wong et al. [6] obtained an average value of the Young’s modulus 1.28 0.5TPa for MWNTs. Atomistic simulations are the powerful tools for investigation of the mechanical properties
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