▎ 摘　　要

We report the mechanical properties (including intrinsic strength, critical failure strain, and Young's modulus) of bilayer graphene with twist or grain boundaries from first-principles calculations. We find that the intrinsic strength and critical failure strain of a bilayer graphene are governed by the twist angle. If a bilayer graphene is formed by one perfect graphene sheet and another graphene monolayer with grain boundaries, its overall mechanical properties are dominated by the layer with grain boundaries. The larger grain boundary angle in bilayer graphene, the higher intrinsic strength it would possess because of the lower energy and shorter C-C bond lengths on the boundary. Owing to the interlayer van de Waals interaction, bilayer graphene with small grain boundary angle presents different behavior from monolayer graphene grain boundaries. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789594]