American Institute of Aeronautics and Astronautics 1 Atomistic Simulation of Carbon Nanotubes with Defects Antonio F. Ávila * , Guilherme R.S. Lacerda † Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, 31270-901, Brazil During carbon nanotubes synthesis a large amount of “defected” ones are generated. The purification process involves, in general, high costs. The market price of single walled carbon nanotubes (SWNT) with 99,999% purity is close to US$500,00/gram. To be able to use these defective nanotubes as reinforcements for composites, their mechanical properties must be known. Considerable work has been done by Gates and his co-workers into the field of carbon nanotubes and composites reinforced by carbon nanotubes. However, the characterization of defective carbon nanotubes, also called hetero-junctions, is still an open question. Notice that hetero-junction properties can have large variations, as those are dependent on the SWNT configurations. The so called molecular mechanics model is employed to investigate two defects configurations, i.e. Dunlap and Sadoc, and their stress concentration regions are located. These regions are the ones with the highest probability of failure. The model is validated against data from literature on non- defective single walled carbon nanotubes with good agreement. I. Introduction s described by Saito and his co-workers 1 , carbon nanotube is a honeycomb lattice rolled into a cylinder. Carbon nanotubes (CNTs) have been the center of many researches due to their dimensions and remarkable electro-mechanical properties. In general, a CNT diameter has a nanometer size and its length can be more than 1µm. Such large aspect ratio (length/diameter) is appointed as one of the reasons for the CNTs notable properties. Consistent with Kalamkarov et al. 2 , single-walled nanotubes (SWNTs) have predicted specific strength around 600 times larger than steel. Another important issue of CNTs is their remarkable thermal and electrical properties. They are thermally stable up to 2800 C (in vacuum), reveal a thermal conductivity about twice as high as diamond, and may exhibit a capacity to carry electric current a thousand times better than copper wires. CNT capabilities have been observed experimentally and verified by numerical simulations. Frankland et al. 3 , Jin and Yuan 4 and Agrawal et al. 5 are among those researchers whom employed molecular dynamics for analyzing carbon nanotubes. The atomistic simulation approach was applied by Belystchko et al. 6 , Lurie et al. 7 , Gates and co- workers 8 while the nano-mechanics modeling was described by Liu et al. 9 , Ruoff and Pugno 10 , and Li and Chou 11 . Although carbon nanotubes have tremendous potential applications in a large variety of usages, e.g. aerospace industry, medical and electronic devices, there is no consensus about their exact mechanical properties. The experiments performed up to now have presented large variability due to the inherent complexity of manipulating these materials. Furthermore, the traditional molecular dynamics (MD) simulations are limited and computationally expensive. In this paper, the concept of molecular structural mechanics described by Li and Chou 11 and Tserpes and Papanikos 12 , and extended by Ávila and Lacerda 13 is associated to the three-dimensional finite element model and later on employed to predict the mechanical properties of defective Single-Walled Carbon Nanotubes (SWNTs),also described as hetero-junctions. Numerical simulations considering the three major configurations (armchair, zigzag and chiral) are prepared for validation purposes. Furthermore, a parametric study on wall thickness, diameter and chirality effects on stiffness is also performed. Finally, the Sadoc and Dunlap hetero-junctions are simulated to be able to identify regions with the highest probability of failure. II. Up to the date research According to Torrones 14 , in 1991 Iijima using a high resolution transmission electron microscope and electron diffraction, reported the existence of helical carbon microtubules (now called nanotubes) consisting of nested graphene tubules . This material was generated in an arc-discharge fullerene reactor (operating at low direct current). * Associate Professor, Department of Mechanical Engineering, 6627 Antonio Carlos Avenue, AIAA Senior Member. Corresponding author, e-mail: aavila@netuno.lcc.ufmg.br , phone: +55 31 3409-5238, FAX:+55 31 3443-3783 † Graduate Research Assistant, Department of Mechanical Engineering, 6627 Antonio Carlos Avenue. A 50th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference <br>17th 4 - 7 May 2009, Palm Springs, California AIAA 2009-2490 Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.