Atomistic simulations of the tensile behavior of graphene fibers

L Zhong and HJ Gao and XY Li, EXTREME MECHANICS LETTERS, 37, 100699 (2020).

DOI: 10.1016/j.eml.2020.100699

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. (C) 2020 Elsevier Ltd. All rights reserved.

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