▎ 摘　　要

As defects play a pivotal role in the mechanical properties of graphene, much research has been underway to understand their specific effects. However, the determination of mechanical properties of defective graphene such as strength and ductility remains challenging, due to the indeterminacy of local stress distributions, potentially released out-of-plane behavior, and multidefect interactions that are involved when subject to external loads. To cast light on the above complexities, in this paper, stress field characteristics of defective graphene are studied via molecular dynamics simulations, which are shown to be strongly dependent on defect geometries. To detail this influence, defect geometries are decoupled into defect size and shape, where the former determines the area shielded from increasing stress and consequently produces low-stress regions, while the latter determines local stress concentration and governs stress distribution along the defect rim. Additionally, it is shown that the nonuniformity of the stress field can potentially release the out-of-plane degree of freedom and therefore induce spatial patterns. To understand the effects of multiple defects in graphene sheets, an analytical strategy of defect grouping is proposed. The obtained understanding of the defect-affected stress distribution is utilized to rationally optimize the collective mechanical properties of defective graphene sheets. We show that even though the mechanical properties of defective graphene sheets vary with different defect geometry, the proportionality of ultimate strength and failure strain is in general preserved. Finally, the relative significance of the system parameters is discussed. This paper systematically discusses the influence of defects on the stress field and collective mechanical properties of graphene, which solidifies the defect-engineering based tuning approach of the mechanics of graphene as well as other two-dimensional materials.