Molecular dynamics simulation of tensile elongation of carbon nanotubes: Temperature and size effects

We report molecular dynamics simulations of tensile elongation of carbon nanotubes (CNTs) over a wide temperature range. In particular, we examine temperature and size effects on tensile ductility of CNTs and compare our results with recent experimental observation on superplastic deformation of CNTs at high temperatures. Our simulations produce substantial tensile ductility in CNTs with large diameters at high temperatures and reveal that similar behavior can be realized over a surprisingly large temperature range between 500 and 2400 K that is yet to be fully explored by experiments. At lower temperatures, tensile deformation modes become brittle due to defect localization attributed to insufficient thermal energy for wide distribution of defect nucleation. For CNTs with smaller diameters, our simulations produce strong defect localization which leads to brittle behavior even at high temperatures. Sensitive dependence on the distribution of incipient defects on thermal energy results in a significant decrease in the elastic limit with increasing temperature. We propose an effective tensile ductility enhancement via temperature reduction beyond the elastic limit. The results offer insights for understanding intriguing temperature effects on tensile deformation modes of CNTs.