Numerical nanomechanics of perfect and defective hetero-junction CNTs

Abstract

Finite element method has been employed in numerical analysis of a wide variety of hetero-junction types in carbon nanotubes with different chiralities and configurations. The investigation does not only include perfect CNTs, but in various studies, several atomic defects, for example, silicon impurities and vacant sites, were introduced to some of the hetero-junction models as well. Therefore, details on the techniques employed for studying the effect of perfect and defective hetero-junction carbon nanotubes on the major mechanical properties is of significant importance. The properties include tensile, torsion, and buckling tests and the influence of the atomic defects on the Young's modulus of hetero-junction carbon nanotubes, numerically. Based on the available results from different mechanical tests on homogeneous tubes, an increase in the diameter of the homogeneous nanotubes of the same length leads to a slight decrease in the shear modulus and vice versa, an increase in the critical buckling loads. However, the Young's modulus of these models remained nearly the same for tubes of the same chiralities. It was also discovered that armchair and zigzag carbon nanotubes had the highest Young's and shear moduli, respectively. The evaluation of the mechanical properties of the hetero-junction carbon nanotubes revealed that the size of their hetero-connection and the diameter of their fundamental tubes significantly dominate their mechanical properties. It was clearly observed that hetero-junction carbon nanotubes had lower tensile stiffness than their corresponding fundamental tubes. However, their shear modulus and critical buckling load lay in the range of the corresponding quantities for their fundamental homogeneous tubes, generally closer to the shear modulus and critical buckling load of their corresponding fundamental thinner tubes. Furthermore, the results from the mechanical tests demonstrated that hetero-junction carbon nanotubes with armchair-armchair and zigzag-zigzag connections have the highest Young's modulus while the shear modulus and critical buckling load peaks were observed in zigzag-zigzag and armchair-armchair hetero-junction models, respectively. Hetero-junction carbon nanotubes with armchair-zigzag kinks also revealed to have the most fragile mechanical properties among the models. Comparison between the obtained moduli and buckling loads of perfect and atomically defective hetero-junction carbon nanotubes clearly illustrated that the atomic defects in the structure of hetero-junction carbon nanotubes cause a linear decline in their mechanical properties, which can be expressed by mathematical relations, in terms of the amount of such defects for the prediction of the mechanical properties of the atomically defective hetero-junction carbon nanotubes.