单层石墨烯薄膜拉伸破坏应变率相关性的分子动力学研究

Strain rate dependences of tensile failure process for single graphene sheet:A molecular dynamics study

采用Tersoff势对扶手椅型(Armchair)和锯齿型(Zigzag)单层石墨烯薄膜在不同应变率条件下的零温单向拉伸破坏过程进行了分子动力学模拟,预测了石墨烯薄膜拉伸破坏的应变率效应.结果表明,石墨烯薄膜的拉伸力学性能具有应变率相关性.当应变率低于5×109s-1时,两种不同手性的单层石墨烯薄膜的拉伸过程经历了一次强化阶段,杨氏模量均随应变率的增大而减小,抗拉强度对应变率不敏感;当应变率高于5×109s-1时,拉伸过程经历了二次强化,尤其锯齿型的,杨氏模量、抗拉强度和对应的拉伸应变均随应变率的增大而显著增大.在不同的应变率下,石墨烯薄膜具有不同的拉伸破坏变形机制.在低应变率下,石墨烯沿主断裂带断裂破坏,而在高应变率下,形成了缺陷簇,具有非晶化特征.

Molecular dynamics simulations with Tersoff bond-order interatomic potential are performed on armchair and zigzag single graphene sheets to investigate the effects of strain rate on their tensile mechanical behavior. The simulation results indicate that the tensile mechanical properties of the sheets are dependent on the strain rate. When the strain rate is lower than 5×10^9s^-1, the tensile process of of both chiral graphen sheets goes through a period of nonlinear hardening for once; the Young＇s moduli decrease with strain rate, while the tensile strength is not sensitive. When the strain rate is higher than 5×10^9s^-1, nonlinear harding occurs twice, especially for the zigzag graphene sheets, which may be related to the deformation mechanisms; in addition, higher strain rates lead to higher Young＇s modulus, tensile strength and corresponding tensile strain. It is also found that the deformation mechanisms of graphene sheets under tension change with the strain rate. For lower strain rate, the graphene fail along the main cracks. While at higher strain rate, clusters of defects are formed which show the feature of amorphization.