Molecular Simulation Study On The Shearing Failure Of Carbon Nanotube/Graphene Interface

Carbon nanotube(CNT) and graphene have lots of outstanding properties, such as high specific strength, high specific modulus, heat-resisting, corrosion-resisting, and high electrical conductivity. They have been used in the field of composite materials, electronics and energy storage containers. The CNT/graphene multi-scale composites extend one-dimensional CNT and two-dimensional graphene to three-dimensional composite materials,at the same time, it keeps the excellent properties of CNT and graphene. But this CNT/graphene materials had not been used widely, partly because of the unstability of interfacial contacting between CNT and graphene. The interfacial failure often happened in the CNT/graphene multi-scale composites. Failure modes of CNT/graphene multi-scale composites have been gradually exposed, including the interfacial peeling failure and interfacial shearing failure. For peeling failure, lots of works have been carried out through molecular simulation and experimental methods. However, few study on the interfacial shearing failure of CNT/graphene has been reported. In order to further uncover the CNT/graphene interfacial shearing failure mechanism, molecular simulation studies on details of shearing failure are carried out. Specifically, the main achievement of this research is as follows:Study on the interfacial shearing failure behavior of CNT/graphene under the van der Waals force is carried out by molecular dynamics method, considering the effect of the size of graphene, the number of the CNT walls and the number of graphene layers on the shearing behavior of CNT/graphene. The results showed that with the increase of shear displacement, shear force changes periodically, and the number of carbon nanotubes walls can affect periodicity of shear force-displacement curves, but the number of graphene layers does not have an impact on periodicity. The critical failure shear force exists at the beginning of the shear process, and the critical failure shear force is affected by the parcel level of graphene and the relative molecular mass corresponding to the parcel area. The larger the parcel area is and the greater the relative molecular mass is, the stronger the critical failure shear force is.Study on effect of graphene hydrogenation ratio on shearing failure behavior of CNT/hydrogenated graphene under the van der Waals force is carried out. The results show that the presence of hydrogen atoms weakens the degree of graphene wrapping carbon nanotube. With the increase of hydrogen atoms, the periodicity of shear force-displacement curve is blurring. The critical failure shear force of CNT/hydrogenated graphene is greater than it calculated by the same size of CNT/graphene. These results indicate the presence of hydrogen atoms improve the shear strength of CNT/graphene.Study on the effect of the ratio of graphene oxidation and the ratio of hydroxyl functional groups on the interfacial shearing failure behavior of CNT/graphene oxide is carried out. The results show an overall increase in the shear force-displacement curve. The presence of functional groups eliminates the periodicity of shear force-displacement curve and exacerbate the volatility of shear force-displacement curve. The critical failure shear force do not appear at the beginning of the shear process any longer. These results indicate the presence of functional groups improve the toughness of the CNT/graphene.Study on the effect of the number of C-C covalent bond on the interfacial shearing failure of CNT/graphene lapped by C-C covalent bond is carried out. The results show that the C-C covalent bond can greatly improve the critical failure shear force of CNT/graphene. One C-C covalent bond can increase the critical failure shear force by 3.97 n N on average. And with the increase of the C-C covalent bond, the failure of CNT/graphene changes from the interfacial shear ing failure to the structure damage of CNT and graphene. These results indicate the C-C covalent bond can greatly improve the lap strength between CNT and graphene.