Plastic Deformation of a Carbon Nanotube Bundle under Transverse Loading

There are numerous examples of crystalline media composed of particles whose shape and size can vary significantly under external loads. As an example of such a medium, this paper models the plastic deformation of a carbon nanotube (CNT) bundle under transverse compression in a two-dimensional setting, considering plane strain of its cross section. A pair of edge dislocations is introduced into the CNT bundle, and their interaction is analyzed as a function of the distance s between their parallel slip planes. Slip in one plane, when s = 0, leads to complete annihilation of the dislocations. If s is negative (positive) and small in absolute value, the interaction of dislocations leads to the formation of vacancies (interstitial CNTs). If | s | > 5, then dislocation dipoles are formed as a result of structural relaxation. Unlike metals, in a CNT bundle, vacancy clusters with more than two vacancies take the form of voidions (local decreasing density in close-packed rows), while interstitial CNTs always form crowdions (local increasing density in close-packed rows). It is shown that the observed effects are caused by deformation (elliptization) of the cross-sections of soft carbon nanotubes at the cores of defects. The obtained results highlight significant differences in the behavior of defects in crystals of deformable particles and in conventional crystals.