A coarse-grained model for the mechanical behavior of multi-layer graphene

Graphene is the strongest and highest weight-to-surface ratio material known, rendering it an excellent building block for nanocomposites. Multi-layer graphene (MLG) assemblies have intriguing mechanical properties distinct from the monolayer that remain poorly understood due to spatiotemporal limitations of experimental observations and atomistic modeling. To address this issue, here we establish a coarse-grained molecular dynamics (CG-MD) model of graphene using a strain energy conservation approach. The model is able to quantitatively reproduce graphene's mechanical response in the elastic and fracture regimes. The hexagonal symmetry of graphene's honeycomb lattice is conserved, and therefore the anisotropy in the non-linear large-deformation regime between the zigzag and armchair directions is preserved. The superlubricity effect, namely the strong orientational dependence of the shear rigidity between graphene layers, is also captured. We demonstrate the applicability of the model by reproducing recent experimental nanoindentation results in silico. Our model overcomes the limitations of current CG-MD approaches, in accurately predicting the fracture properties, the interlayer shear response, and the intrinsic anisotropy of MLG. Additionally, our fast, transferable force-field can be straightforwardly combined with existing coarse-grained models of polymers and proteins to predict the meso-scale behavior of hybrid carbon nanomaterials.