In this thesis, grain boundary effects on nanoindentation of Fe bicrystal using molecular dynamic was investigated. Particularly, mechanical properties of iron bicrystal with ?5 grain boundary were calculated by molecular dynamic simulation of nanoindentation. The spherical shape indenter was used for nanoindentation. An embedded atom method interatomic potential for Fe was used for this simulation. Grain boundary effect was investigated by performing indentation simulation at different distances from the grain boundary. The effect of grain boundary on the elastic modulus, maximum shear stress and hardness of Fe bicrystal was investigated. Several load drops were detected from the obtained loading curves. These load drops are the result of the initiation of dislocation nucleation and so the transition from purely elastic to elastic- plastic deformation. The results also indicate that the maximum shear stress on the grain boundary is lower than its value far from the grain boundary. A brief dislocation reaction analysis is performed on some simulation snapshots. In addition, an algorithm was proposed and used for implementation of EAM force field on GPUs which is faster than its similar CPU codes. In the following, the grain boundary energy of symmetric and asymmetric iron bicrystals is calculated for ?3, ?9 boundaries with ?110? tilt axis and ?5 with 100 tilt axis using molecular dynamics simulations with the embedded-atom method potential. A modified method for creating grain boundary atomic structure is proposed that has sufficient accuracy and its computation cost will be considerably lower than the previously used methods. The effect of three parameters namely rigid body movement, overlapping distance, and reduction side is investigated and compared to previous studies and the optimal parameters are introduced which leads to a better performance in bicrystal modeling. Keywords : Symmetric and asymmetric grain boundary, Nano-indentation, Mechanical properties, Grain boundary energy, Molecular dynamics
