A Multiscale Mechanical Study for the Design of the Lightweight Materials Based on Hierarchical Carbon Nanotubes

Description

The proposed project aims to develop a theoretical and numerical framework for understanding and characterizing the mechanical characteristic of a lightweight material constructed from hierarchical super carbon nanotubes (HSCNTs) based on the combination of atomic-based cellular automata algorithm (ACAA) and continuum mechanics. In the hierarchical material, the primary structure is the single walled carbon nanotubes (SWCNTs). The secondary structure is the super carbon nanotubes (SCNTs) fabricated from the primary structure (i.e. SWCNTs). The tertiary structure is the lowest-level HSCNTs fabricated from the secondary structure (i.e. SCNTs). Similarly, a higher-level structure is fabricated from lower-level structures and, thus, the structure formed in this way is a hierarchical structure. Carbon nanotubes (CNTs), SCNTs and HSCNTs are formed by rolling a graphene sheet, a sheet fabricated by CNTs and a sheet fabricated by SCNTs, respectively, at specific angles (chiral). The combination of the rolling angles (chiralities) decides the properties of the structures. A structure generated hierarchically from SCNTs or higher-level structures is known as hierarchical super carbon nanotubes (HSCNTs). As SWCNTs, SCNTs and HSCNTs are hollow shell structures, the structure fabricated by them is a lightweight material. Through the synthesis of HSCNTs with manipulated chirality and hierarchy, a macro/nano-sized material with unique properties can be formed because the properties are dependent on the chirality at various levels of structures from the lowest-level structures (SWCNTs) to higher-level structures (SCNTs and HSCNTs). A comprehensive understanding of the macro/nano-sized materials made from HSCNTs can be achieved by developing an appropriate multi-scale theoretical framework. Thus, this project aims to develop a multi-scale mechanics model in which both primary CNTs and secondary SCNTs are treated as a discrete system at the atomic scale because they are in nanoscale, but HSCNTs will be treated as macroscopic materials because the size of the structure is in macro scale. Material properties of SCNTs with different chirality will be obtained using a modified ACAA algorithm based on the Tersoff-Brenner many-body potential. At the micron scale of the tertiary or higher-level structure (i.e. HSCNTs), the constitutive relationship will be developed as a function of the elastic constants at different chirality of the primary and the secondary structures using molecular structure mechanics. Based on the developed constitutive law, a multi-scale theoretical framework will be established for the analysis and design of HSCNT-constructed materials (HSCMs) with specific high performance. This is the key towards achieving practical application of this new class of material.