Pullout forces and friction in multiwall carbon nanotubes

Molecular dynamic calculations of pullout in multiwall carbon nanotubes (CNTs) demonstrate that inner walls with fractured ends have pullout forces ~3-4 times larger than those for capped ends, due to deformation of the fractured end, quantitatively accounting for experiments. Under pressure, Amonton's law applies to an area of contact at the fractured end, with μ=0.13--0.33. Defects in the CNT walls affect the force, suggesting a mechanism for the observed stick-slip behavior and an increase of pullout force with decreasing embedded length. The results have implications for CNT composite strength and toughness.