Investigate the constrained-microplasticity of nano-polycrystal silicon in nanomachining using atomic simulation method

Nano-polycrystal materials with smaller grain are difficult to prepare which makes it difficult to study the deformation process using experiments. Molecular dynamics (MD) method has already been proved to be an efficient toolkit for nanoscale phenomenon and gradually adopted to study the mechanical response of specimen with internal grains separated by high angle boundaries without porosities and impurities. The results demonstrate that partial dislocation activity takes over in nanocrystalline materials if the grain sizes are larger enough. Transverse deformation perpendicular to the feeding direction is generated and leads to the moving side-flow and the size of which is gradually increased with feeding. The stress distribution of side-flow is different from substrate which justifies its independent physical property. The anisotropic distribution of surface height (unmachined-surface, the aera ahead of cutting tool) is induced with feeding. No anisotropic-surface-height is observed in the machined surface which indicates that plastic deformation will eliminates the different mechanical response resulted by the crystal orientation at atomic scale. Different grain shape and crystal orientation initialized different boundary conditions, which lead to different force transmitting paths thus result in discontinuous deformation. The discrete-plasticity is typical characteristic of polycrystal machining process.