Department of Mechanical Engineering and Science, Kyoto University, Nishikyo-ku, Kyoto 615-8540, Japan.
Nanoscale. 2017 Nov 16;9(44):17325-17333. doi: 10.1039/c7nr04443g.
Multilayer graphene consists of a stack of single-atomic-thick monolayer graphene sheets bound with π-π interactions and is a fascinating model material opening up a new field of fracture mechanics. In this study, fracture behavior of single-crystalline multilayer graphene was investigated using an in situ mode I fracture test under a scanning electron microscope, and abnormal crack propagation in multilayer graphene was identified for the first time. The fracture toughness of graphene was determined from the measured load-displacement curves and the realistic finite element modelling of specimen geometries. Nonlinear fracture behavior of the multilayer graphene is discussed based on nonlinear elastic fracture mechanics. In situ scanning electron microscope images obtained during the fracture test showed asynchronous crack propagation along independent paths, causing interlayer shear stress and slippages. We also found that energy dissipation by interlayer slippages between the graphene layers is the reason for the enhanced fracture toughness of multilayer graphene. The asynchronous cracking with independent paths is a unique cracking and toughening mechanism for single-crystalline multilayer graphene, which is not observed for the monolayer graphene. This could provide a useful insight for the design and development of graphene-based composite materials for structural applications.
多层石墨烯由单层石墨烯片通过π-π 相互作用堆叠而成，是一种迷人的模型材料，开辟了断裂力学的新领域。在这项研究中，首次使用扫描电子显微镜下的原位 I 型断裂试验研究了单晶多层石墨烯的断裂行为，并识别出多层石墨烯中的异常裂纹扩展。通过测量的载荷-位移曲线和对试样几何形状的实际有限元建模确定了石墨烯的断裂韧性。基于非线性弹性断裂力学讨论了多层石墨烯的非线性断裂行为。在断裂试验过程中获得的原位扫描电子显微镜图像显示，裂纹沿独立路径异步扩展，导致层间剪切应力和滑移。我们还发现，石墨烯层之间的层间滑移引起的能量耗散是多层石墨烯断裂韧性增强的原因。具有独立路径的异步开裂是单晶多层石墨烯独特的开裂和增韧机制，而在单层石墨烯中则观察不到。这为设计和开发用于结构应用的基于石墨烯的复合材料提供了有用的见解。
