Toughness Enhancement by Aligned Multi-Walled Carbon Nanotubes Pullout from Polymer Matrix of Multi-Scale Composites

Abstract

There have been tremendous researches on carbon nanotubes (CNTs) and CNTs reinforced composites due to their excellent mechanical, electromagnetical and thermal properties. Radially aligned multi-walled CNTs grown in situ on the surface of carbon fiber or its woven fabric by the chemical vapor deposition method not only provide the significant three-dimensional reinforcement, but also overcome the poor dispersion of nanostructures. In order to investigate how the aligned multi-walled CNTs affect the mechanical properties of the multi-scale composites, a representative volume element is used to simulate the multi-walled CNT pullout process by means of the finite element method. Related influencing factors are taken into consideration: CNT length, CNT Youngs modulus, and the shear strength of the interface between multi-walled CNTs and epoxy matrix, which is characterized by a cohesive zone model. The results reveal that the aligned multi-walled CNTs make a significant contribution to the fracture toughness of the multi-scale composites, and the CNT/epoxy composites with high toughness require relatively high interfacial shear strength, reasonable CNT length and Youngs modulus. The study is helpful for the optimal design of multi-scale composites.