Study on Comprehensive Mechanical Properties of Metallic Matrix CNT Nano-composites

Carbon nanotubes (CNT) have excellent mechanical strengths, electrical conductivity, and thermal conductivity. CNT reinforced metallic nano-composites are viewed as a great candidate to replace traditional alloy materials. It has been shown that CNTs can greatly enhance the strength, thermal conductivity, and electrical conductivity of composites. However, the ductility of composites would deteriorate due to the addition of CNTs if the fabrication or/and processing methods are not improved or well designed. This dissertation investigated (1) the strengthening mechanisms of CNT on metallic matrix, such as mechanical strength and thermal conductivity, and (2) analytical modeling on the strength-ductility trade-off of CNT reinforced composites under different temperatures and loading conditions. This work involves many experiments, finite element (FE) simulations, and analytical model studies. In experiments, different types of pure copper specimens were designed and tested under a wide range of loading conditions. These experimental data provided the baseline of pure copper\u27s ductility characteristics for composite study. Both analytical method and finite element analysis were used to study the strengthening mechanisms of CNT reinforced aluminum matrix composites. For the analytical analysis, the Orowan looping effect, thermal mismatch effect, and load bearing effect are considered all together. A series of finite element analyses using representative volume element (RVE) method were conducted considering influences of CNTs aspect ratios, volume fraction of hardened zone, and the hardened plastic strain of hardened zone. The results show that the aspect ratio of CNTs is very important in the strengthening of CNT reinforced nano-composites. A digital workflow was proposed to investigate the mechanical and thermal properties of composites, and a three dimensional (3D) RVE method was implemented for the analysis and achieved better accuracies. The influence of CNT anisotropy was also studied based on the digital workflow. At last, the strength-ductility trade-off phenomenon was thoroughly investigated, and a new analytical solution considering different loading conditions and elevated temperatures was proposed and verified by experimental data of Cu/CNTs