Liu Feng, Tang Qiheng, Wang Tzu-Chiang
State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing, 100190, China.
School of Engineering Science, University of Chinese Academy of Sciences, Beijing, 100049, China.
Small. 2017 Jul;13(25). doi: 10.1002/smll.201700028. Epub 2017 May 16.
Due to lack of the third dimension in 3D bulk materials, the crack tip in graphene locates on several atoms implying that its fracture behavior can be closely associated with its lattice structure, i.e., the bond length and angle. As the bond length reflects the discrete nature of the atomic structure, theoretical discussion is focused on the concomitant size effect at the nanoscale with few or no reports about the influence of the bond angle. Through the comparisons between theoretical calculations and experimental data, here it is first demonstrated that the bond angle is essential for understanding the fracture behavior in graphene, serving as an intrinsic notch reducing the stress singularity near the crack tip (the intrinsic notch effect), leading to the breakdown of the Griffith criterion in graphene. The work provides a framework for the studying of the brittle fracture in 2D materials, which gives rise to the more reliable device design based on 2D materials. More importantly, the significance of the intrinsic notch effect is profound and far-reaching, paving the way to a more comprehensive and deep understanding of the mechanical properties in nano as well as nanostructured materials.
由于三维块状材料缺乏第三维，石墨烯中的裂纹尖端位于几个原子上，这意味着其断裂行为可能与其晶格结构密切相关，即键长和键角。由于键长反映了原子结构的离散性质，理论讨论集中在纳米尺度上伴随的尺寸效应，而关于键角影响的报道很少或没有。通过理论计算与实验数据的比较，本文首次证明键角对于理解石墨烯的断裂行为至关重要，它作为一种内在缺口降低了裂纹尖端附近的应力奇异性（内在缺口效应），导致石墨烯中格里菲斯准则的失效。这项工作为研究二维材料的脆性断裂提供了一个框架，这有助于基于二维材料进行更可靠的器件设计。更重要的是，内在缺口效应的意义深远，为更全面、深入地理解纳米材料以及纳米结构材料的力学性能铺平了道路。
