Atomistic and Continuum Modelling of Strength and Adhesion of Graphene

Exceptional electromechanical properties of graphene (a single layer of graphite) have been used to develop the next generation of nanodevices. These state-of-the-art nanodevices, such as sensors and transistors, have a profound impact in numerous engineering disciplines, ranging from biomedicine to aerospace. Recent experiments show that graphene could also be used as an ultra-strong reinforcement for composite materials. In both nanodevices and composite materials, graphene is in contact with adjoining materials, creating mechanically weak interfaces between them. Therefore, understanding the mechanical behaviour of both graphene and graphene interfaces is critically important in designing reliable graphene-based systems. In this thesis, molecular dynamics simulation studies are conducted to gain a basic understanding of the mechanics of graphene-based systems. Then, based on this knowledge, computationally efficient continuum-based models are developed in order to further investigate the strength and adhesion of nanoscale systems. The continuum-based models are accurate and around one million times faster than the molecular dynamics simulations. In addition, using the concepts of kinetic analysis, an analytical model is developed to estimate the strength of defective graphene. Finally, a nonlinear spring model is developed to characterize the adhesion properties of defective graphene interfaces. Results show that defects and temperature significantly reduce the strength of graphene. Low concentrations of hydrogen adatoms degrade the interfacial adhesion of graphene interfaces, and highly hydrogen functionalized graphene completely loses its strength when subjected to higher temperatures. It is also found that molecular dynamics simulations, conducted at elevated temperatures and high strain rates, significantly over predict the strength. Furthermore, the study reveal that graphene with vacancy defects shows a singular stress field as in continuum fracture mechanics and moderate amount of lattice trapping prevails in graphene.