In recent years, a large number of experimental studies have shown that graphene fibers, a new type of carbon fiber consisting of many monolayers of wrinkled and curved graphene sheets aligned in the axial direction of the fiber, exhibit high tensile strength and many functionalities. Although much effort has been devoted to improving their mechanical properties, the underlying deformation mechanism of graphene fibers under tension still remains unclear. Here, we construct simulation models of graphene fibers with diameters of 10 and 20 nm using wrinkled graphene sheets with topological defects, hereafter referred to as graphene ruga sheets, as building blocks via a combination of the phase field crystal method and atomistic modeling. We then perform a series of large-scale molecular dynamics simulations of the constructed graphene fibers under uniaxial tension. Our simulation results revealed that the graphene fibers undergo plastic deformation with stress flow and that their tensile strength (i.e., the peak stress in the stress–strain curve) and Young’s modulus increase with decreasing fiber diameter, which is mainly attributed to the decrease in the number of defects with reduced fiber diameter. Our simulations further revealed that the tensile strength is related to nanocrack nucleation/initiation from nanovoids or sharp corners between neighboring fused graphene sheets, while the flow stress is determined by interlayer slipping between neighboring graphene layers. Furthermore, we investigated the influence of structural continuity on the tensile strength of graphene fiber. The results showed that the tensile strength increases 1.9-3.5 times with the improvement in the structural continuity of graphene fibers within the investigated range. Our simulations provide mechanistic insights into the deformation mechanism of graphene fibers, which may be used to guide their design and fabrication.

近年来，大量的实验研究表明，石墨烯纤维是一种新型的碳纤维，由许多单层起皱和弯曲的石墨烯片沿纤维的轴向排列而成，具有很高的拉伸强度和许多功能。尽管已投入大量努力来改善其机械性能，但石墨烯纤维在张力下的潜在变形机理仍然不清楚。在这里，我们通过相场晶体方法和原子建模相结合，使用具有拓扑缺陷的起皱的石墨烯片（以下称为石墨烯ruga片）构建了直径为10和20 nm的石墨烯纤维的模拟模型。然后，我们对在单轴张力下构造的石墨烯纤维进行一系列大规模的分子动力学模拟。我们的模拟结果表明，石墨烯纤维会随着应力流而发生塑性变形，其抗张强度（即应力-应变曲线中的峰值应力）和杨氏模量会随着纤维直径的减小而增加，这主要是由于石墨烯纤维的减小所致。纤维直径减小的缺陷数量。我们的模拟进一步表明，抗张强度与相邻的熔融石墨烯片之间的纳米空隙或尖角产生的纳米裂纹成核/起始有关，而流动应力则取决于相邻石墨烯层之间的层间滑动。此外，我们研究了结构连续性对石墨烯纤维拉伸强度的影响。结果表明，在研究范围内，随着石墨烯纤维结构连续性的提高，拉伸强度提高了1.9-3.5倍。我们的仿真为石墨烯纤维的变形机理提供了机械方面的见解，可用于指导其设计和制造。