COUPLING EFFECTS OF WRINKLES AND GRAIN BOUNDARY ON THE FRACTURE OF GRAPHENE

Graphene fabricated via chemical vapor deposition (CVD) is typically polycrystalline and also includes many wrinkles. The fracture of the polycrystalline graphene with wrinkles under an uniaxial tensile load is investigated via molecular dynamics simulations. With a tensile load perpendicular to the grain boundary, wrinkles can significantly increase the failure stress of bi-crystalline graphene with a small tilt angle, and the increase in the failure stress is up to around 50%. The wrinkle effect on the failure stress decreases with the increase of the tilt angle, resulting in that the failure stress of bi-crystalline graphene is insensitive to the tilt angle and slightly lower than that of pristine graphene, which agrees with the experimental results very well. With a tensile load along the grain boundary, the failure stress is insensitive to the wrinkle. In addition, wrinkles can significantly increase the failure strain, up to 100%. The influence mechanism can be described as follows: wrinkles will cause the out-of-plane deformation in graphene, resulting a partial release of the tensile pre-stress induced via the 5-7 rings of the grain boundary and consequently an increase in the failure stress of bi-crystalline graphene; the interaction between 5-7 rings of the grain boundary is eliminated, resulting that the failure stress is insensitive to the tilt angle; the flattening of wrinkles can significantly decrease the stretching ratio of C---C bonds, resulting an obvious increase in the failure strain. The present study provides a useful help to understand the fracture of graphene.