Simulation of mechanical behavior of nanomaterials by molecular statics

Standalone films with thickness around nanometer under different loading conditions have been analyzed using molecular statics with embedded-atom-method (EAM) potentials to study the size dependence of mechanical properties (both elastic and plastic). It was found that the mechanical properties are highly size dependent at nano scale and the dependence would be different depending on the loading condition and crystal orientation. It was also observed that the elastic constants for the nano film at some crystal orientations and loading conditions could exceed their bulk values. The wavy film was also considered to study the surface roughness effect on the nucleation of dislocations. The dislocation problem in film and substrate system was also studied. In this research, continuum model based on the distortional energy was proposed for determining the film critical thickness. It was found that, in comparison with other existing continuum models, the distortional energy model could significantly improve the accuracy in critical thickness predictions. The surface roughness effect on the dislocation nucleation in the film-substrate system was also examined using molecular statics. Different interfaces (coherent and incoherent) were constructed to study the size effect for multilayer system. The elastic properties over a range of modulation wavelengths were calculated. It was found that no enhancements of the elastic constants were found for either incoherent or coherent interface. Meanwhile, some issues related to the molecular study with the adoption of different interatomic potential, i.e. pair Morse and many-body EAM potential, on the prediction of mechanical properties were also discussed. The molecular statics results with both EAM potentials and Morse potentials showed similar trend in the size dependence of mechanical properties, both elastic and plastic, even though the molecular calculation adopting Morse potential tended to overestimate the values