Carbon nanotubes as strong fibers in CNT-composites are subjected to large deformations in radial direction. They provide strength as well as structural damping in the composite. Despite being strong in the axial direction, CNTs are rather soft in the radial direction.

I. Arias and M. Arroyo, Size-Dependent Nonlinear Elastic Scaling of Multiwalled Carbon Nanotubes, Phys. Rev. Lett. 100, 085503 (2008).

Size matters for the mechanics of multiwalled carbon nanotubes (MWCNTs). It has been known for some time that MWCNTs often wrinkle under deformation exhibiting the so-called rippling deformation pattern, which makes MWCNTs much softer. Through large-scale multiscale simulations we have characterized with a power law the softer wrinkled response, and showed that the transition strain between the super-stiff behavior attributed to MWCNTs and this softer regime scales as the inverse of the tube diameter. Thus, the tera Pascal Young’s modulus can be fully exploited in devices and materials only for moderately sized tubes. Similarly, in interpreting experiments or designing devices, the classical Euler-Bernouilli beam theory can only be applied to such tubes. The elasticity of thicker tubes is nonlinear, typically display mixtures of wrinkled and unwrinkled sections, and often exhibit hysteretic mechanical behavior.

See http://imechanica.org/node/2395 for a related post.

PRL 99, 175503 (2007);   Jianyu Huang, Feng Ding, Kun Jiao, Boris I Yakobson

Youtube Movie:  http://www.youtube.com/watch?v=NSNlE8AreeM    http://www.nature.com/nnano/reshigh/2007/1107/full/nnano.2007.404.html

Generation of open ends carbon nanotubes coordinates (atomic positions) is easy and the generation of cap for these carbon nanotubes is extremely difficult. Some of the half-fullerenes (C60, C240, C540…) fit as a cap for the armchair and zigzag nanotubes. NanotubeModeler  (http://www.jcrystal.com/products/wincnt/index.htm) software generates the carbon nanotubes with cap but they are limited to few armchair and zigzag configurations.

Huang, Nano Lett. 7, 2335 (2007); Philip Ball, Nature 448, 396 (2007)
Watch movies at: http://pubs3.acs.org/acs/journals/supporting_information.page?in_manuscr...  

Huang et al., PRL 98, 185501 (2007)

Watch movies at: http://netserver.aip.org/cgi-bin/epaps?ID=E-PRLTAO-98-002719

We report exceptional ductile behavior in individual double-walled and triple-walled carbon nanotubes at temperatures above 2000 C, with tensile elongation of 190% and diameter reduction of 90%, during in situ tensile-loading experiments conducted inside a high-resolution transmission electron microscope. Concurrent atomic-scale microstructure observations reveal that the superelongation is attributed to a high temperature creep deformation mechanism mediated by atom or vacancy diffusion, dislocation climb, and kink motion at high temperatures. The superelongation in double-walled and triple-walled carbon nanotubes, the creep deformation mechanism, and dislocation climb in carbon nanotubes are reported here for the first time.