Graphene and its elemental analogue: A molecular dynamics view of fracture phenomenon

Abstract

Abstract-Graphene and some graphene like two dimensional materials; hexagonal boron nitride (hBN) and silicene have unique mechanical properties which severely limit the suitability of conventional theories used for common brittle and ductile materials to predict the fracture response of these materials. This study revealed the fracture response of graphene, hBN and silicene nanosheets under different tiny crack lengths by molecular dynamics (MD) simulations using LAMMPS. The useful strength of these two dimensional materials are determined by their fracture toughness. Our study shows a comparative analysis of mechanical properties among the elemental analogues of graphene and suggested that hBN can be a good substitute for graphene in terms of mechanical properties. We have also found that the pre-cracked sheets fail in brittle manner and their failure is governed by the strength of the atomic bonds at the crack tip. The MD prediction of fracture toughness shows significant difference with the fracture toughness determined by Griffth's theory of brittle failure which restricts the applicability of Griffith's criterion for these materials in case of nano-cracks. Moreover, the strengths measured in armchair and zigzag directions of nanosheets of these materials implied that the bonds in armchair direction have the stronger capability to resist crack propagation compared to zigzag direction.

Failure in Two-Dimensional Materials: Defect Sensitivity and Failure Criteria

“…Thus, anisotropic properties lead to different crack propagation paths in graphene under tensile loading. In addition, temperature and other defects may also affect the crack propagation [50,97].…”

Tuning the mechanical properties of silicene nanosheet by auxiliary cracks: a molecular dynamics study

“…Even though the pristine structure of silicene has a very high fracture strength, 28,29 fracture toughness of silicene is signicantly lower than most of the conventional engineering materials. 30 This offers a challenge in the fabrication of silicene based nanoelectronic devices. In general, fabrication of 2D materials involve various structural aws such as defects and cracks.…”

“…16,31,32 These inherent aws signicantly reduce the ultimate stress of the materials because of the high local stress concentration region. 29,30,33,34 Numerous investigations have been conducted to probe the fracture mechanism of 2D nanosheets with pre-existing cracks. 7,35 Specically, the failure mechanism of single crystal and nanocrystalline silicene have been extensively studied 30,36 due to the challenge concerning the fabrication method.…”

“…29,30,33,34 Numerous investigations have been conducted to probe the fracture mechanism of 2D nanosheets with pre-existing cracks. 7,35 Specically, the failure mechanism of single crystal and nanocrystalline silicene have been extensively studied 30,36 due to the challenge concerning the fabrication method. Yuan et al 29 investigated the mechanical properties of armchair silicene nanoribbons containing an edge crack using molecular dynamics (MD) simulations.…”

“…19,20,42 Also, the fracture behavior of silicene is much different than graphene. Previously, Rakib et al 30 investigated the comparative mechanical properties and fracture toughness of graphene, silicene and hexagonal boron nitride. Chung et al 43 showed that unlike graphene, the stress in the silicene nanosheet is nonuniformly distributed due to the rearrangement of atoms in the silicene nanosheet via ring reorientation under applied strain.…”