Minimum grain size and compression mechanical behavior of polycrystalline graphene based carbon honeycombs: Cell irregularity and grain size effect

The graphene-based carbon honeycombs (CHCs) have excellent mechanical properties and various applications, and have attracted intensive attention recently. However, the real CHCs in experiments have random cell shapes. The effects of polycrystallinity and cell irregularity on the mechanical properties of CHCs are still unknown. Here, first, we investigate the minimum cell size stability with ideal cell walls in the polycrystalline graphene-based carbon honeycombs (PGCHs). Then, based on molecular dynamics simulations, the compressive mechanical properties of four PGCHs with typical cell irregularities are studied systematically, including the periodic regular graphene-based carbon honeycombs (RGCHs) with a zero-degree cell irregularity. Under in-plane compression, the Young’s modulus, initial peak stress, mean plateau stress, and per volume energy absorption W_v of RGCHs and PGCHs decrease significantly with increasing grain size, and show a pseudo Hall–Petch relation. The mean plateau stress and W_v of PGCHs are higher than those of RGCHs. Under out-of-plane compression, the grain size effect is also obvious. However, the influence of cell irregularity is very small and can be ignored. The results indicate that the Hall–Petch relations of polycrystalline materials are dependent on both grain size and cell irregularity, and provide theoretical guidance for real CHCs in engineering applications.