Graphene derivatives and metamaterials, fabricated through chemical functionalization and defect engineering of graphene sheets, have major potential for technological applications because of their exceptional thermomechanical properties that can be tuned by tailoring of their nanostructural features. Here, we report a systematic computational study on the thermomechanical behavior of a class of two-dimensional (2D) carbon-based nanostructures, namely, nanodiamond superstructures in interlayer-bonded twisted bilayer graphene, formed through hydrogenation-induced interlayer covalent bonding of twisted bilayer graphene with commensurate bilayers. We have conducted a comprehensive classification of all such superstructures that can be formed with respect to the corresponding structural parameters, including the commensurate bilayer’s twist angle, the interlayer bond pattern and density, and the concentration of
sp3-bonded C atoms in these superstructures. We report results for the mechanical behavior of such carbon nanocomposite superstructures based on molecular-dynamics (MD) simulations of uniaxial straining tests according to a reliable interatomic bond-order potential and establish the dependence of the superstructures’ mechanical properties on the concentration of
sp3-bonded C atoms. We also define a ductility metric and demonstrate that a brittle-to-ductile transition occurs in these superstructures with increasing the concentration of
sp3-bonded C atoms beyond a critical level. The underlying ductile fracture mechanism, mediated by void formation, growth, and coalescence, in contrast to the typical brittle fracture of graphene is characterized, and the superior mechanical response to uniaxial straining of the ductile nanodiamond superstructures is demonstrated.
Furthermore, we study the mechanical response of these superstructures to nanoidentation based on MD simulations of nanoindentation tests. We establish the dependences of the elastic modulus and the hardness of the superstructures on their structural parameters as well as on indentation parameters. The resulting structural response of the superstructures under nanoindentation testing also is characterized in detail. Finally, we report results for the lattice thermal conductivity of these superstructures based on non-equilibrium MD simulations of thermal transport. We report a significant reduction in the lattice thermal conductivity with increasing concentration of sp3-bonded C atoms in the superstructures, which is promising for thermal management applications, and establish the dependence of the lattice thermal conductivity on the full range of structural parameters for these interlayer-bonded bilayer materials.
