Molecular-Dynamics Analysis of Nanoindentation of Graphene Nanomeshes: Implications for 2D Mechanical Metamaterials

Abstract

We report results of a comprehensive computational study of the mechanical response to nanoindentation of graphene nanomeshes (GNMs) or nanoporous graphene, namely, single-layer graphene sheets with periodic arrangements of nanopores, based on molecular-dynamics simulations of nanoindentation tests according to a reliable interatomic bond-order potential. We find the GNMs’ response to indentation to be nonlinearly elastic until fracture initiation, with elastic properties that depend strongly on the GNM porosity but are not sensitive to pore edge passivation, which, however, influences the GNM failure mechanism past fracture initiation. Increasing GNM porosity leads to a monotonic decrease of the 2D elastic modulus of the GNMs, and the modulus–porosity dependence follows a quadratic scaling law. The maximum stress reached at the GNM breaking point is high throughout the porosity range examined, even at very high porosity. The maximum deflection of the indented GNMs at their breaking point exhibits a minimum at porosities below 20%; beyond this critical porosity, the maximum deflection increases monotonically with increasing porosity and can reach values comparable to half of the indented sample radius at high porosities. Such high deformability is interpreted on the basis of the C–C bond length and stress distribution over the GNM at its breaking point. Moreover, our analysis reveals an inelastic, dissipative necking mechanism of GNM failure at high porosities that further enhances the excellent deformability of the GNMs. Our findings highlight the potential of graphene nanomeshes as 2D mechanical metamaterials whose mechanical response can be tuned by proper tailoring of their structural features.

Molecular-Dynamics Simulations on Nanoindentation of Graphene-Diamond Composite Superstructures in Interlayer-Bonded Twisted Bilayer Graphene: Implications for Mechanical Metamaterials

“…Figure c shows the force–displacement curves for the four superstructures that have exhibited the most pronounced inelastic responses; these superstructures have the lowest f sp 3 values among all the IB-TBG superstructures examined. As opposed to the smooth F (δ) curves generated in the nanondentation simulations of graphene nanomeshes, four force–displacement curves in Figure c, corresponding to f sp 3 values of 1.18%, 1.65%, 2.46%, and 4.05%, exhibit noticeable kinks that imply a nonlinear inelastic response. In these superstructures, each nanodiamond cluster formed between the two graphene layers consists of only three interlayer bonds, which is the smallest nanodiamond cluster that can be created for this type of commensurate bilayer graphene structures.…”

“…In the simulations, the cutoff distance of the Lennard-Jones part of the AIREBO potential is equal to 10.2 Å and the C−C cutoff distance is set to 2.0 Å to avoid unrealistically high stresses to develop in the sample at high deflections. 21,36,60 A similar setup to that in the study of nanoindentation of graphene nanomeshes 61 has been employed in this work.…”

“…Moreover, detailed comparisons between the DFT and AIREBO predictions of the structure and energetics of graphite and the bulk phases of cubic diamond and hexagonal diamond (lonsdaleite), as well as of interlayer-bonded structures with C–C covalent bonding between the concentric graphene walls of multiwalled carbon nanotubes have been reported in ref . In the simulations, the cutoff distance of the Lennard-Jones part of the AIREBO potential is equal to 10.2 Å and the C–C cutoff distance is set to 2.0 Å to avoid unrealistically high stresses to develop in the sample at high deflections. ,, A similar setup to that in the study of nanoindentation of graphene nanomeshes has been employed in this work.…”

Exceptionally Long Covalent CC Bonds—A Local Vibrational Mode Study

“…The local mode force constants can quickly be calculated after a routine frequency calculation and therefore, can provide important guidance for the synthesis of a compound with a C−C bond of a particular strength. Work is in progress to investigate long CC bonds in nanotubes and crystals under pressure at ambient temperature [ 139 , 140 , 141 , 142 , 143 ].…”

Fracture Mechanism of Nanocomposite of Metal and Graphene with Defect Pores

“…Due to influence of preparation conditions, the graphene is also subject to structural defects, which can significantly alter its properties. [34][35][36][37] Based on computer simulations of nanoindentation, Chen et al [38] investigated the mechanical properties of graphene with different numbers of pores. Their results showed that the response of nanoporous graphene to indentation is non-linearly elastic and its elastic properties strongly depend on the porosity of nanoporous graphene.…”