The Stability Researches On The Tensile Mechanical And Morphological Properties Of Graphene

Graphene has attracted a great deal of attention in various scientific communities due to its extraordinary mechanical, electrical and physical properties. It is thus considered as a promising candidate for thermoelectric fiber reinforced materials, super sensitive sensors and nano-electronic devices. Studying the mechanical properties of graphene has theoretical guidance for its applications. Meantime, the mechanical or electrical properties of graphene have obvious dependence on temperature. So in the second part of this thesis, the common effects of the chirality, width of graphene nanoribbons (GNRs) and simulation temperature on the tensile properties of GNRs are studied by molecular dynamics method in the range of1K to800K. The results show that the Young’s modulus of GNRs varies with different edges, but slightly dependent on the GNRs width. The Zigzag GNRs have larger Young’s modulus and tensile strength than other four types of GNRs. The results also show that the tensile strength of GNRs obviously reduces as the temperature increase. In addition, we also study the uniform variable temperature process. The effects of the initial temperature, variable rate of temperature and the final temperature on the tensile mechanical properties of GNRs are studied. The results show that when the the variable rate of temperature is less than2K/ps, the tensile strength increases with the variable rate of temperature. When the variable rate of temperature is greater than2K/ps, the tensile strength will no longer changes. Compared with the effect of initial temperature on the tensile strength, the final temperature shows obvious effect on the tensile strength of the GNRs.As graphene is flexible, the graphene morphology can be affected by substrate, and the electrical characteristics of graphene can be influenced by its morphology. Understanding morphological properties of graphene is important for a number of potential applications. As the dimension of specimen becomes close to the order of the micro-structural length scale, the size effect plays an important role in mechanical properties of materials. So in the third part of our thesis, the morphology and snap-through transition of multilayer graphene on a corrugated elastic substrate were studied. The surface roughness of substrate is determined by amplitude and wavelength. Based on the couple stress theory, a theoretical model was developed to understand the size effect on graphene morphology. Two cases of graphene on substrate were considered. In the first case of freely sliding of graphene on substrate, the results indicate that the surface amplitude has no effect on corrugation of graphene, it only affects the critical condition of snap-through transition. And the transition will happen when the thickness of the graphene reaches a certain value. The wavelength not only affects the critical condition of snap-through transition, but also the morphology of graphene. For the limiting case of no graphene sliding, the amplitude and the wavelength all has obvious on morphology of graphene, and graphene with different layers all appear snap-through transition when the substrate stiffness reaches a certain value. The results show that the snap-through transition is comprehensive results caused together by appropriate substrate stiffness, graphene thickness and substrate surface roughness. Snap-through transition is more likely to happen when graphene is thicker, substrate is stiffer and surface roughness is higher. Moreover, the results show obvious size effect on graphene morphology when surface roughness is higher and substrate is compliant. This part of work offers a theoretical guidance for controlling graphene morphology by changing the substrate surface roughness in certain case.Many practical systems which have elastic substrate with inhomogeneous stiffness are often encountered in various natural and artificial materials and devices, so it is essential to understand morphological properties of graphene to promote the number of potential applications, such as device fabrication, transparent conductors and composite materials. In the fourth part of the thesis, the graded parameters and size effect on buckling of graphene were studied. And in the last part, we study the snap-through transition and morphology of multilayer graphene on an elastic substrate, which have two types of grading modulus. The effects of substrate thickness, substrate graded parameter and the Poisson’s ratio of substrate on graphene morphology are theoretically analyzed. For the first limiting case, graphene always completely conforms to the substrate surface when graphene is thinner enough or substrate is stiffer enough. Graphene is more likely to remain flat when the graphene is thicker, the substrate is thicker or the substrate grade is higher. The results also show that the Poisson’s ratio of substrate has influence on the snap-through critical values of monolayer graphene in the second limiting case. From the work, the substrate graded parameter is proved to be a dominated factor to control the morphology and snap-through transition of graphene. Our results can support the theoretical guidance for controlling graphene morphology by changing the substrate thickness and substrate grade.This paper from the perspective of graphene mechanical properties and morphology stability, further study the dependence of tensile mechanical properties on size, chirality and temperature, and stability properties dependence on substrate stiffness, thickness and graded factor. Our study provides a theoretical basis for controlling graphene morphology and its further applications.