Abstract
Structure evolution and mechanical response of the carbon nanotube (CNT) bundle under lateral biaxial compression is investigated in plane strain conditions using the chain model. In this model, tensile and bending rigidity of CTN walls, and the van der Waals interactions between them are taken into account. Initially the bundle in cross section is a triangular lattice of circular zigzag CNTs. Under increasing strain control compression, several structure transformations are observed. Firstly, the second-order phase transition leads to the crystalline structure with doubled translational cell. Then the first-order phase transition takes place with the appearance of collapsed CNTs. Further compression results in increase of the fraction of collapsed CNTs at nearly constant compressive stress and eventually all CNTs collapse. It is found that the potential energy of the CNT bundle during deformation changes mainly due to bending of CNT walls, while the contribution from the walls tension-compression and from the van der Waals energies is considerably smaller.
Highlights
Carbon atoms can create a huge number of allotropes because four valence electrons can form the sp1, sp2 and sp3 bond configurations
The action of van der Waals forces produces a variety of secondary structures including structures with a translational symmetry such as fullerite crystal [1,2,3], graphite [4,5], and crystals made of carbon nanotubes (CNTs) [6,7,8]
In the existing works devoted to the mechanics of CNT bundles, little attention was paid to the discussion of structure evolution under lateral compression up to large strain levels
Summary
Carbon atoms can create a huge number of allotropes because four valence electrons can form the sp , sp2 and sp bond configurations. In the experimental study [52] it has been shown that the deformation of CNT bundles under non-hydrostatic pressure becomes irreversible for pressures above 5 GPa. Experimental and computational works on mechanical properties of CNTs have been discussed in the review [53]. In the existing works devoted to the mechanics of CNT bundles, little attention was paid to the discussion of structure evolution under lateral compression up to large strain levels. This problem is interesting from the standpoint of fundamental science because materials with highly deformable structural units should have peculiar mechanical properties and CNT bundle is an example of such material, as CNT cross section can obtain various shapes under pressure. The efficiency of the chain model in modelling secondary sp2 -carbon structures such as folded and scrolled carbon nanoribbons has been demonstrated in a series of works [69,70,71,72,73,74,75]
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