Auxetic Behaviour of Re-entrant Cellular Structured Kirigami at The Nanoscale

Abstract

Some typical two-dimensional (2D) materials are active elements used in nano-electro-mechanical systems (NEMS) design, owing to their excellent in-plane physical properties on mechanical, electrical and thermal aspects. Considering a component with a negative Poisson’s ratio used in NEMS, the adoption of kirigamis made of periodic re-entrant honeycomb structures at the nanoscale would be a feasible method. The focus of this thesis work is to investigate the specific auxetic behaviour of this kind of structures from typical tailored 2D materials. By employing the numerical simulation method: molecular dynamics simulation, the auxetic behaviour of re-entrant cellular structured kirigami is discussed thoroughly and concretely. Three main effects of a re-entrant cellular structured kirigami are systematically simulated, and then analysed and discussed here. They are size effect, surface effect and matrix effect of 2D materials. The study begins with a demonstration that a kirigami with specific auxetic property obtained by adjusting the sizes of its honeycombs. Making use of molecular dynamics experiments, the size effect on auxetic behaviour of the kirigami is discussed. The results show that, in some cases, the auxetic difference between the microscopic structured kirigami and macroscopic structure kirigami is negligible, which means the results from macro-kirigami could be used to predict the auxetic behaviour of nano-kirigami. Surface effect of kirigami is also illustrated from two aspects. The one is to identify the difference of mechanical responses between pure kirigami and hydrogenated kirigami at some geometry and loading condition. And another is from the difference of mechanical responses between microstructure kirigami and continuum kirigami under the same loading condition and geometric configuration. Graphene is selected as the major 2D material in the study. As kirigami tailored from various 2D materials would exhibit different mechanical behaviour, graphene, single-layer hexagonal boron nitride (h-BN) and single-layer molybdenum disulphide (MoS2) are selected as representative 2D materials to investigate the influence of this effect, without loss of generality.