The effect of agglomeration and slightly weakened CNT–matrix interface on free vibration response of cylindrical nanocomposites

Abstract

Estimation of the effective homogenized properties is an essential step in the application of carbon nanotube (CNT)-reinforced composites. The difference between the experimental results and continuum-based homogenization schemes has motivated this work to present a modified Mori–Tanaka homogenization approach for CNT-reinforced nanocomposites. The agglomeration of CNT fibres in the matrix phase and slight weakening of the CNT–matrix interface are considered, which are incorporated in the effective homogenized properties of the nanocomposites using a two-parameter agglomeration model and interface spring-layer model, respectively. The nanotube fibres in the well-dispersed form are considered as cylindrical inclusions in the isotropic polymeric matrix. The bundled structure of CNTs is first modelled as cylindrical inclusions in the matrix and later as cumulative spherical inclusions in the hybrid matrix. Further, the effective material properties of nanocomposites are used to study the free vibration response of cylindrical panels reinforced with CNT fibres. Efficient higher-order shear and normal deformation theory is adopted, and fundamental natural frequencies are evaluated for a different set of agglomeration and interface weakening parameters using an analytical approach. The results show a significant reduction in the material stiffness as well as the natural frequency with increasing degree of agglomeration. At the same time, a slightly weakened interface is found less severe for stiffness reduction. An analysis of straight aligned CNTs highlighted their larger vulnerability to agglomeration than randomly distributed CNTs in the matrix.