Temperature-dependent brittle-ductile transition of α-graphyne nanotubes under uniaxial tension

As a novel one-dimensional full-carbon allotrope, the tensile property of alpha-graphyne nanotubes (alpha-GNTs) under different temperatures was studied with the reactive molecular dynamics method. A very interesting phenomenon of temperature-dependent brittle-ductile transition for carbon nanomaterials was found no matter what the chirality of the alpha-GNT is. The alpha-GNT shows a brittle behavior with an ultimate strain of -0.2 at relatively low temperatures. When the temperature is higher than a critical temperature, it exhibits a ductile behavior with an ultimate strain of -0.4. The ultimate strain first decreases and then increases with the increase of temperature. The fundamental mechanism of such a brittle-ductile transition phenomenon was first revealed, which is mainly due to the thermal activation energy-controlled microstructure evolution. Beyond the critical temperature, the atomic structures around some hexagonal corners in alpha-GNTs would recombine through the continuous formation and annihilation of some new triangular structures. Such a mechanism is totally different from the Stone-Wales defect-induced brittle-ductile transition mechanism in carbon nanotubes (Nardelli et al, Phys. Rev. Lett, 1998, 81 (21): 4656). The influence of temperature on the other physical parameters of alpha-GNTs, such as the Young's modulus, yield strength, ultimate stress, was also systematically studied. The results in this paper, especially the brittle-ductile transition mechanism, would be of great help to the subsequent study and application of alpha-GNTs .