a b s t r a c tThe plastic flattening of a sinusoidal metal surface is studied by performing plane strain dislocation dynamics simulations. Plasticity arises from the collective motion of discrete dislocations of edge character. Their dynamics is incorporated through constitutive rules for nucleation, glide, pinning and annihilation. By analyzing surfaces with constant amplitude we found that the mean contact pressure is inversely proportional to the wavelength. For small wavelengths, due to interaction between plastic zones of neighboring contacts, the mean contact pressure can reach values that are about 1/10 of the theoretical strength of the material, thus significantly higher than what is predicted by simulations that do not account for size dependent plasticity. Surfaces with the same amplitude to period ratio have a size dependent response, such that if we interpret each period of the sinusoidal wave as the asperity of a rough surface, smaller asperities are harder to be flattened than large ones. The difference between the limiting situations of sticking and frictionless contacts is found to be negligible.
Molecular dynamics simulations are performed to demonstrate that the graphene nanoribbon (GNR) could helically wrap onto and insert into the single-walled carbon nanotube (SWNT) to form helical configurations, which are quite close to the helices found in nature. The steady decline of the potential energy suggests that the helical wrapping and insertion are spontaneous. The van der Waals interaction, π–π stacking interaction between the GNR and the SWNT, and dangling σ-orbitals on carbon atoms at open edges of GNR are all responsible for these unique phenomena. Two GNRs would form a DNA-like double-helix with the same handedness. The dependence of the diameter and chirality of SWNT and the width of GNR in the helix-forming process are investigated. The gaps on the tube walls are not good at the helical wrapping and insertion. In addition, we explore the possibility of using the spontaneous wrapping and insertion of GNRs to deliver substances. These unique properties are expected to provide novel strategies to design nanoscale vehicles and substantial functional devices.
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