Compression behavior of carbon nanotube bundles and individual carbon nanotubes within the bundle has been studied by using the Suzuki, Shanker, and usual Tait formulations. It is found that the Suzuki formulation is not capable of explaining the compression behavior of nanomaterials. Shanker formulation slightly improves the results obtained by the Suzuki formulation, but only usual Tait’s equation (UTE) of state gives results in agreement to the experimental data. The present study reveals that the product of bulk modules and the coefficient of volume thermal expansion remain constant for carbon nanotubes. It has also been found that the individual carbon nanotubes are less compressible than bundles of carbon nanotubes. 1. Introduction After their discovery by Iijima [1] carbon nanotubes have got a lot of attention because of their unique electronic and mechanical properties, but the most important property of carbon nanotubes is their elastic response to the external force or stress [2, 3]. As a one-dimensional structure, carbon nanotubes can be thought of as one sheet or multiple sheets of graphene rolled into a cylinder. Single-walled carbon nanotube bundles typically consist of several nested tubes, each like a graphene sheet bent into the cylindrical form with an overall diameter of a few nanometers. According to different chiral angles, single-walled carbon nanotubes can be classified into zigzag ( ), armchair ( ), and chiral tubes ( ) [4]. The Young’s modulus and Poisson’s ratio of nanotube have been studied by the previous workers [5–9], while the hardness as one of the most important parameters characterizing the mechanical properties of single-walled carbon nanotubes has been intensively studied during the last decade [6, 10]. High pressures which are encountered from deep down the earth to the astrophysical objects may cause many effects such as compression, pressure ionization, modification in electronic properties, phase changes, and several phenomenons in applied fields [11]. For this, pressure versus volume relations of condensed matter known as equation of state is a vital input. Many equations of state exist in the literature, but still there is a need to judge on their suitability under whole range of compressions as most of them give the same result under small compression. In high pressure, generally used theory is the finite strain theory which means the theory due to Birch [12]. However, Birch’s theory rates no more than a passing mention as discussed in detail by Stacy [13]. The attention has also been given to the theory based
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