Radial carbon nanotube
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Carbon nanotubes (CNTs) are basically long hollow cylinders of graphite sheets. Although a graphite sheet has a 2D symmetry, carbon nanotubes by geometry have different properties in axial and radial directions. It has been shown that CNTs are very strong in the axial direction[1]. Young's modulus on the order of 270-950 GPa and tensile strength of 11-63 GPa were obtained.
On the other hand, there were evidences that in the radial direction they are rather soft. The first TEM observation of radial elasticity suggested that even the van der Waals forces can deform two adjacent nanotubes[2]. Later, nanoindentations were performed by several groups to quantitatively measure radial elasticity of multiwalled carbon nonotubes [3], [4]. Young's modulus of on the order of several GPa showed that CNTs are in fact very soft in the radial direction.
Radial direction elasticity of CNTs is important especially for carbon nanotube composites where the embedded tubes are subjected to large deformation in the transverse direction under the applied load on the composite structure.
