Study On Mechanical Deformation And Evolution Of Internal Voids Of Graphene

Graphene is a sheet of carbon atoms arranged in a two-dimensional hexagonal lattice.It is the thinnest and strongest material ever measured with strength exceeding more than two hundred times of steel. Graphene has been researched in the front of material science recently, as with graphene has fascinating properties and attracted many researchers.However, in the experimental synthesis, it is inevitable to get the polycrystalline graphene composed of many different grain boundaries(GBs). So, it is important to clarify the gain boundaries effects in graphene for future widely use.In this paper, the molecular dynamics was adopted to simulate graphene with different grain boundary 21.8°、32.2°、38.2°、60°. By this way the influence of symmetric tilt GB on the bend degree and deformation of graphene was studied under a compress stress, and the potential of graphene with different grain boundaries was compared. Simultaneously, the perfect graphene model was also considered. The results show that the bend degree of graphene with GB is bigger than those of the perfect graphene under compress stress, the bending position and the bending radius of perfect graphene are different from those of graphene with GB. The potential energy of the graphene on GB is higher than that of the surrounding, and the potential energy of pentagon ring is bigger than that of the heptagon ring. Moreover, the deformation behavior of multi-layer perfect graphene is different.Under compress stress, the maximum gathering layers for three to nine-layers graphene is three layers, while that for eight layers graphene is four.The effect of voids and GBs defects on the uniaxial tensile fracture mechanism of graphene sheet investigated by molecular dynamics simulation with Adaptive Intermolecular Reactive Empirical Bond Order(AIREBO) potential function. The results show that during the drawing process, C-C bond was stretched and the graphene deformation severely, then crack initiation, and finally pulled off on GB for the graphene with GBs. While the graphene with big void and GBs, C-C bond around voids was stretched, and the hexagon ring was extanded to pentagon ring, heptagon ring, octagon ring under tensile stresses, small voids stretched to big voids, the graphene sheet damaged at the big voids under the tensile stresses. Graphene with GBs and void far from GBs, under thetensile stresses, different sizes and shapes lattice defects appeared around voids and C-C bond on GBs was elongated along the stretched direction,as with tensile stress increase the defects around voids grow up and rupture on void finaly, the GBs will be restored to the state before stretching after graphene rupture. Visible, the big void defects make graphene more easily be destroyed, while the graphene has big void and GBs at the same time defects was present around big voids firstly and destroyed on big void. So big voids’ weaken degree is larger than GBs on graphene.