EVALUATION OF THE MECHANICAL PROPERTIES OF CARBON NANOTUBE COMPOSITES BY FINITE ELEMENT ANALYSIS

Abstract

Carbon nanotubes (CNTs) possess extremely high stiffness, strength and resilience, and therefore carbon nanotubes provide ultimate reinforcing materials for the development of nanocomposites. Evaluating the effective material properties of such nanoscale materials is one of the important tasks. Simulations using molecular dynamics and continuum mechanics models can play significant roles in this development. Currently, the continuum approach seems to be the only feasible approach for such large scale analysis. The finite element method based continuum mechanics has been used to evaluate the mechanical properties of CNT-based composites. The cylindrical as well as square representative volume element (RVEs) has been utilized in these simulations. Formulas to extract the effective material constants for the cylindrical and square RVEs under an axial stretch load case are derived based on the elasticity theory. An extended rule of mixtures based on the strength of materials theory for estimating the effective Young's modulus and poison's ratio is applied for the comparison of FEM solutions with the elasticity theory based solutions. It has been observed that the addition of the CNTs in a matrix at volume fractions of only about 3.6%, the stiffness of the composite is increased by 33% for long CNT at E`/E' = 10, whereas there is no much improvement in stiffness has been noticed in case of short CNTS at E`/E' =40. These results suggest that short CNTs in a matrix may not be as effective as long CNTs in reinforcing a composite. The comparisons of mechanical properties between cylindrical and square RVE have also been made for single CNT based composite. Since, the mechanical properties obtained through cylindrical RVE overestimates the Young's modulus, thereby the square RVE is preferred for the simulations. The mechanical properties using cylindrical and square RVEs are also evaluated for multiple CNTs based composites, and compared with each other.