▎ 摘　　要

We investigate the deformation and fracture behaviors of pristine and bi-crystalline graphenes by molecular dynamics simulations. For pristine graphene with a pre-crack, fracture toughness is strongly dependent on the crack morphology and atomic configuration at the crack tip. For bi-crystalline graphene, fracture toughness becomes comparable to that of pristine graphene with increase in density of topological 5-7 defects arranged uniformly along grain boundary due to cancellation of the dipole stress field. In addition, we find that trans-intergranular transition can occur during the rupture process with increase in the slant angle of grain boundary with respect to the external loading direction. Our findings provide a fundamental understanding of failure mechanisms and fracture behaviors in graphene and other twodimensional materials. (C) 2016 Elsevier B.V. All rights reserved.