Fracture behaviors of brittle and ductile 2D carbon structures under uniaxial tensile stress

Abstract Many novel two-dimensional (2D) allotropes of carbon have been predicted to be (meta)stable at 0 K, however, their thermal stability and mechanical properties at finite temperatures remain unclear. In this study, the mechanical properties and fracture behaviors of five newly predicted monatomic thick carbon sheets (C 31 , C 33 , δ-graphyne (GY), γ-GY, C 63 , and graphene) are investigated using molecular simulations. The δ-GY, γ-GY, and graphene show brittle fractures in uniaxial tension testing at temperatures from 1 to 1200 K. The first signs of fracture in these brittle carbon sheets indicate that the C C bonds linking the benzene rings and linear acetylenic carbons break with strong directional preference, whereby the direction of the breaking C C bonds is parallel to the direction of tensile stress. A brittle-to-ductile transition is identified in the C 31 , C 33 , and C 63 sheets at high temperatures, which corresponds to the breakages of the C C bonds in the triangular carbon rings. Global and local order-order structural transitions as well as order-disorder transitions are obtained in different ductile carbon sheets, and are found in the same carbon sheet under tensile stress along different directions. These results suggest a strong correlation between the structure and the failure mechanism in 2D carbon sheets, which is of great importance in the future design, synthesis and application of novel 2D materials.