EFFECTS OF IMPERFECTIONS ON THE ELASTIC PROPERTIES OF CARBON NANOTUBES

Nanotubes are useful for not only strengthening polymer based materials that are of widespread use in aerospace applications, but also for their nondestructive testing. Nanotubes with defects are now routinely manufactured. Their manufacture without defects is still prohibitively expensive. Thus, it becomes important to be able to identify the defect percentage in the nanotubes, because the defects cause reduction in both strength and stiffness and electrical conductivity. The elastic properties of carbon nanotubes with imperfections are studied using a model based on structural mechanics. The carbon - carbon bonds are modeled as load bearing beams joined together by the carbon atoms. The mechanical properties of a bond are obtained from a relationship between structural mechanics and molecular mechanics. The carbon nanotubes are drawn forming this structure and the stiffness matrix of the nanotube is obtained from the assembly of the stiffness matrix of each bond. The obtained results for carbon nanotubes without imperfections are verified by comparing them to previous works. Furthermore, the number of degrees of freedom of each atom is reduced from six to three by neglecting the moments. This simplifies the model, reduces the computation time and allows the test of larger nanotubes with a low impact on the accuracy of the results. Finally, different percentages of imperfections are introduced in the nanotubes in the form of missing atoms and the evolution of the Young's modulus with randomly imposed imperfection percentage is obtained. This relationship turned out to be almost linear when the imperfections percentage is small. The results obtained allow the prediction of the quality of carbon nanotubes from the elastic properties observed in experimental tests. If the Young's modulus of some nanotubes is found, then it can be directly related to a percentage of imperfections. The minimum number of necessary experimental tests to obtain statistically accurate results is also discussed.