Although graphene is believed to be the strongest material, many properties of this material are still worth exploring and discovering, especially the influence of inevitable defects in its preparation on the mechanical and fracture properties which are of high significance. This work provides a new feasible way to study the mechanical and fracture properties of graphene. The novelties of this study are threefold: (1) A novel peridynamic (PD) model is proposed for polycrystalline graphene in which grains of large size exist; (2) The coupling effect of the pre-crack length and the grain size on the inverse pseudo Hall-Petch relation is revealed; (3) The results confirm the applicability of classical Griffith theory in brittle fracture analysis of graphene. Based on the proposed PD model, dependence of the mechanical and fracture properties on the grain size which changes from a few to hundreds of nanometers is investigated in this study. The fracture forms of graphene are consistent with the experimental observations. Based on the Griffith theory, the obtained fracture toughness such as K_c (i.e. 3.8$\text{MPa}\sqrt{\mathrm{m}}$ - 6.3$\text{MPa}\sqrt{\mathrm{m}}$) or G_c (i.e. 14.0 J/m² – 40.9 J/m²) is comparable with previously reported theoretical and experimental values, which proves the validity of the proposed PD model. Besides, the fracture toughness can be greatly enhanced by the blunt pre-crack tip. This work presents insights into mechanical failure of graphene and guidance on fragmentation of graphene for its practical use.

虽然石墨烯被认为是最强的材料，但该材料的许多性能仍然值得探索和发现，特别是其制备过程中不可避免的缺陷对力学和断裂性能的影响具有重要意义。这项工作为研究石墨烯的力学和断裂性能提供了一种新的可行方法。这项研究的新颖之处有三个：（1）针对存在大尺寸晶粒的多晶石墨烯提出了一种新的近场动力学（PD）模型； (2)揭示了预裂纹长度和晶粒尺寸对逆伪Hall-Petch关系的耦合效应； (3)结果证实了经典格里菲斯理论在石墨烯脆性断裂分析中的适用性。基于所提出的 PD 模型，本研究研究了机械和断裂性能对从几纳米到数百纳米变化的晶粒尺寸的依赖性。石墨烯的断裂形式与实验观察结果一致。根据格里菲斯理论，得到断裂韧性如K_c（即3.8$\text{兆帕}\sqrt{\mathrm{米}}$- 6.3$\text{兆帕}\sqrt{\mathrm{米}}$) 或 G_c （即 14.0 J/m² – 40.9 J/m²）与之前报道的理论和实验值相当，证明了有效性所提出的 PD 模型。此外，钝的预裂纹尖端可以大大提高断裂韧性。这项工作提出了对石墨烯机械失效的见解，并为石墨烯的实际应用提供了碎裂指导。