Role of Ripplocations in Bending and Uniaxial Compression of Graphite

Here 60 graphene layers were loaded uniaxially, UA, along the zig-zag configuration, or by double indentation, DI, normal to the basal planes and modeled with molecular dynamics simulations. In the linear elastic regime, under UA loading, the total energy, Etot, primarily reflects straining of the C-C bonds, EC-C, with a modulus of approximate to 800 GPa. Following linear elasticity, both cases form ripplocation boundaries, RBs, spontaneously. Consistent with buckling, the energy per atom to nucleate RBs in the UA configuration is nearly twice that of the DI case. The remote strain, ctot, for buckling is 0.3 % in the DI configuration, and 0.5 % for the UA case. As ctot increases post-buckling, the interlayer van der Waals bond energy, EvdW, increases. In the DI case, a local minimum correlated with a face-centered stacking of the graphite layers is observed at ctot approximate to 2 %. Cycling significantly reduces the energy per atom to nucleate RBs, endowing the graphite a memory effect. The deformation indicates that nucleation of RBs is more challenging than their movement. The process is almost fully reversible up to ctot approximate to 30 %, after which, in the DI case, the layers delaminate, pinning the RBs, resulting in partial reversibility. Postdelamination configurations obtained in our simulations quite closely resemble experimental observations, validating our approach. Crucially, the Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) potential is not good enough to model the mechanical deformation of graphite; the dihedral-angle-corrected registry-dependent interlayer potential (DRIP) results in much more realistic results.