Mechanical response of the carbon nanotube bundle to uniaxial and biaxial lateral compression followed by unloading is modeled under plane strain conditions. The chain model with a reduced number of degrees of freedom is employed with high efficiency. During loading, two critical values of strain are detected. Firstly, period doubling is observed as a result of the second order phase transition, and at higher compressive strain, the first order phase transition takes place when carbon nanotubes start to collapse. The loading-unloading stress-strain curves exhibit a hysteresis loop and, upon unloading, the structure returns to its initial form with no residual strain. This behavior of the nanotube bundle can be employed for the design of an elastic damper.

Studies on thin sheets and related materials are of high importance nowadays because of their great potential in various applications. The latest success in the production of graphene opens many new opportunities for the construction of novel three‐dimensional carbon nanostructures that exhibit good mechanical and electronic properties together with high specific surface area. Such novel nanostructures based on graphene sheets are very promising for energy storage devices, supercapacitors and stretchable electronics, to name a few. In this work, the mechanical responses of new bulk carbon nanostructures under hydrostatic pressure or shear strain are investigated, respectively, via molecular dynamics simulations. The size effect of the structural units on the strength of crumpled graphene is analyzed. The studied bulk carbon nanostructures are found to be extremely stable against diamondization. It is shown that the structures and mechanical properties of bulk carbon nanomaterials can be altered by severe plastic shear deformation. Shear strain leads to the formation of stable structures, even at relatively small strain.

Diamond‐like carbon nanostructures with cubic anisotropy made by joining fullerene‐like molecules of different types via valence bonds are studied by means of molecular dynamics simulations. The considered structures are interesting because they include both sp2‐ and sp3‐hybridized carbon atoms, which lead to their distinct properties compared to the structures with one type of hybridization. Seven diamond‐like carbon phases having different shapes of structural units and/or different ways of their connection are studied in the present work. For the relaxed equilibrium structures, the engineering elastic constants (Poisson's ratio, Young's modulus, and shear modulus) are calculated as the functions of the crystal orientation angles. Extreme values of the elastic constants are reported. It is shown that two of the considered diamond‐like structures have negative Poisson's ratio and can be regarded as the partial auxetics. According to the results of the present study, elastic properties of the bulk diamond‐like carbon structures can vary considerably depending on their structure. Diamond‐like carbon nanostructures

Close packed carbon nanotube bundles are materials with highly deformable elements, for which unusual deformation mechanisms are expected. Structural evolution of the zigzag carbon nanotube bundle subjected to biaxial lateral compression with the subsequent shear straining is studied under plane strain conditions using the chain model with a reduced number of degrees of freedom. Biaxial compression results in bending of carbon nanotubes walls and formation of the characteristic pattern, when nanotube cross-sections are inclined in the opposite directions alternatively in the parallel close-packed rows. Subsequent shearing up to a certain shear strain leads to an appearance of shear bands and vortex-like displacements. Stress components and potential energy as the functions of shear strain for different values of the biaxial volumetric strain are analyzed in detail. A new mechanism of carbon nanotube bundle shear deformation through cooperative, vortex-like displacements of nanotube cross sections is reported.

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Diamond‐like structures, that include sp2 and sp3 hybridized carbon atoms, are of considerable interest nowadays. In the present work, various carbon auxetic structures are studied by the combination of molecular dynamics (MD) and analytical approach. Two fullerites based on the fullerene C60 and fullerene‐like molecule C48 are investigated as well as diamond‐like structures based on other fullerene‐like molecules (called fulleranes), carbon nanotubes (called tubulanes) and graphene sheets. MD is used to find the equilibrium states of the structures and calculate compliance and stiffness coefficients for stable configurations. Analytical methods are used to calculate the engineering elastic coefficients (Young's modulus, Poisson's ratio, shear modulus and bulk modulus), and to study their transformation under rotation of the coordinate system. All the considered structures are partial auxetics with the negative value of Poisson's ratio for properly chosen tensile directions. It is shown that some of these structures, in a particular tension direction, have a very high Young's modulus, that is, 1852 GPa for tubulane TA6.

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