Micromechanics-based modeling of elastic modulus and coefficient of thermal expansion for CNT-metal nanocomposites: effects of waviness, clustering and aluminum carbide layer

Abstract

A micromechanical model is analytically developed to estimate the elastic modulus and the coefficient of thermal expansion (CTE) of the carbon nanotube (CNT)-reinforced metal matrix nanocomposites (MMNCs). The effects of two important microstructural features, including the CNT clusters and the waviness on the thermo-elastic response are investigated. The formation of aluminum carbide (Al4C3) layer due to the interaction between the CNT and the metal matrix is considered. A good agreement is found between the available experimental data and the simulation results considering the waviness, clustering, and Al4C3 interphase. The influences of volume fraction, and dispersion type of CNTs and Al4C3 layer thickness on the elastic modulus and the CTE of the CNT-metal nanocomposites are examined. The non-straight shape and the clustering of CNTs are two critical factors that can significantly degrade the thermo-elastic properties. From the mechanical viewpoint on designing the CNT-metal nanocomposites, producing the homogeneous microstructure without the CNT clusters and using the straight CNTs are necessary factors to obtain the maximum level of the thermomechanical performances. The numerical results show that the formation of the Al4C3 interphase may improve the MMNC macroscopic engineering constants. It is observed that aligning the CNTs into the metal matrixes leads to a significant improvement in the MMNC thermo-elastic properties. The proposed micromechanical approach can be a suitable model to predict the elastic modulus and the CTE of the CNT-reinforced MMNCs considering the important microstructural features.