Orientation dependence of the fracture behavior of graphene

• Published in: Carbon (New York) Vol. 66; pp. 619 - 628
• Main Authors: Jhon, Young I., Jhon, Young Min, Yeom, Geun Y., Jhon, Myung S.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.01.2014; Elsevier
• Subjects: Anisotropy; Brittle fracture; Computer simulation; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Elasticity; Exact sciences and technology; Fatigue, brittleness, fracture, and cracks; Fracture mechanics; Fullerenes and related materials; diamonds, graphite; Graphene; Materials science; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Orientation; Physics; Specific materials; Tensile strength; Orientation; Graphene; Ruptures
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2013.09.051

Graphene has unique mechanical properties in that it is simultaneously very strong and stretchy, which severely hampers the prediction of its orientation-dependent fracture behavior based on conventional theories used for common brittle or ductile materials. For the first time, by exploring the entire range of available tensile orientations, this study reveals the unique anisotropic fracture response of graphene using molecular dynamics simulations. We found that, as the uniaxial tensile direction rotates from armchair (0°) to zigzag orientation (30°), both the tensile strength and strain remain almost constant up to an orientation angle of ∼12°, then they rapidly increase (exponential growth), resulting in a remarkable degradation of the tensile strength compared to brittle fracture counterpart (inverse-sinusoidal growth). This typical fracture pattern holds for 100–700K. We propose a model that can explain its physical origin in good agreement with the simulation results. We also found that the elastic behavior of graphene is quasi-isotropic for all tensile orientations, in contrast to its anisotropic fracture behavior. Using indentation simulations of graphene, we showed that the anisotropic/isotropic features of fracture/elasticity are also well-preserved in the two-dimensional tensile systems but its fracture anisotropicity is greatly attenuated due to the inherent sixfold symmetry of graphene.