It was recalled that layer-structured nanomaterials, where alternating layers of nanocrystallites met along high-angle grain boundaries, were a special category of nano-material. An investigation was made here of the effect of the presence of a vacancy, upon the elastic constants of such materials, by using atomistic simulations. The calculations were performed on a model system in which atoms interacted via a Lennard–Jones potential, and the elastic constants were obtained within the framework of homogeneous deformations, for nanocrystallite layer-widths ranging from 2.24 to 37.12nm. The results showed that the favoured position of the vacancy was in the grain-boundary core. The state of relaxation of the structure was an important factor affecting the obtained results. In both the unrelaxed and relaxed structures, the results converged to a given value after the 5th (310) layer. This value seemed to depend upon the size of the nanocrystallite, and approached the bulk value above a given size. It was concluded that, in the case of a relaxed system, there was a smoother variation of the system energy and elastic constants as a function of the distance of the vacancy from the grain-boundary plane when the size increased. The manner in which external stresses were applied to the system affected the values of the elastic properties that were obtained; with those constants which were related to the characteristic directions of the grain boundary being the ones most affected.

Vacancy Effect on the Elastic Constants of Layer-Structured Nanomaterials. T.E.Karakasidis, C.A.Charitidis: Theoretical and Applied Fracture Mechanics, 2009, 51[3], 195-201