▎ 摘　　要

Graphene is a thin sheet with special properties and complicated mechanical behavior. It's important to study graphene experimentally and theoretically. Stone-Wales defects, cracks and atom vacancy are popular defects in carbon allotropes especially in graphene. In this paper, effect of center cracks on graphene was discussed. At first, mechanical properties of non-defected graphene sheet was obtained using molecular dynamics simulation. Comparing result with theoretical and experimental studies showing good agreements and proofing the results. Then, 8 different cracks were considered in center of graphene sheets. Stress-strain curves of defected graphene sheets with different tension strain rates were plotted. The results showed that increasing crack length lead to decreasing Young's modulus of graphene from 905GPa to 697GPa. Also, fracture occurred in less tensile strain. In the following, structural molecular mechanics method was used to simulate cracked graphene sheets. The results showed good agreement between two methods.