A feasibility study on the fracture strength measurement of polycrystalline graphene using nanoindentation with a cylindrical indenter
A feasibility study on the fracture strength measurement of polycrystalline graphene using nanoindentation with a cylindrical indenter
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DOI：
10.1016/j.carbon.2016.06.004
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发表时间：
2016-10
期刊：
影响因子：
10.9
通讯作者：
Jihoon Han;Seunghwa Ryu;Dongwoo Sohn
中科院分区：
文献类型：
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作者：
Jihoon Han;Seunghwa Ryu;Dongwoo Sohn
由于难以进行单轴拉伸测试，原始石墨烯及其晶界（GB）的强度主要通过球形尖端的纳米压痕来测量。然而，我们最近表明，球形压头的断裂力不能直接映射到单轴强度。在本文中，采用一系列分子动力学模拟与断裂力学分析相结合，证明圆柱形压头的断裂力可以直接映射到单轴拉伸下石墨烯的强度。在圆柱形尖端或单轴拉伸的压痕下，具有低倾斜角的晶界的石墨烯片的破裂与晶界处裂纹成核的开始同时发生。相反，当被球形压头尖端压入时，石墨烯片承受压痕载荷，直到裂纹尺寸与尖端半径相当。此外，结果表明，使用圆柱形压头估计强度对压痕位置以及可能由人为错误或设备限制引起的角度偏差不太敏感。我们的工作提出了从纳米压痕实验获得拉伸强度的可行性，这可能为测量石墨烯和相关二维材料的拉伸强度提出新的标准。
The strength of pristine graphene and its grain boundaries (GBs) are mainly measured by nanoindentation with a spherical tip due to the difficulty of conducting uniaxial tensile tests. However, we recently showed that the fracture forces from the spherical indenter cannot be directly mapped onto the uniaxial strength. In this paper, employing a series of molecular dynamics simulations combined with a fracture mechanics analysis, we demonstrate that the fracture force from cylindrical indenters can be directly mapped onto the strength of graphene under uniaxial tension. Under indentation with cylindrical tips or uniaxial tension, the rupture of graphene sheets that have GBs with a low-tilt angle occurs simultaneously with the onset of crack nucleation at the GBs. On the contrary, when indented by a spherical indenter tip, the graphene sheets sustain the indentation loads until the crack size becomes comparable to the tip radius. Furthermore, the results show that estimating the strength with a cylindrical indenter is not very sensitive to the indentation site as well as angular misalignments that can be caused by human error or the limitations of the apparatus. Our work presents the feasibility of obtaining the tensile strength from nanoindentation experiments, which may suggest a new standard to measure the tensile strength of graphene and related two-dimensional materials.