Integrated MD simulation of scratching and shearing of 3D nanostructure

An integrated MD simulation of scratching and shearing with one specimen is conducted to analyze the nanomachining mechanism and mechanics properties of nanostructures. Simulation results indicate that during scratching the onset and propagation of dislocations depend on the scratch depths; during shearing, the yielding stress of a small-size nanostructure is more sensitive to nanomachining imperfection and residual defects. Dislocations nucleate first near the burr in a scratched specimen. In an ideal nanostructure or a nanostructure with shallow scratched groove, the distribution of stress is generally lower and flatter. As the depth of groove increases, high stresses transit from the corner to either end of groove, especially near the burr or around the location of tool withdraw. During the deformation of nanostructures, shear stress plays a leading role in the elastic stage, and both normal stress gradients and shear stress determine the onset and evolvement of defects in the plastic stage. When the ratio of the depth of groove to the height of specimen is up to one third, the scratched groove determines the breakpoint of a nanostructure. The fluctuation of shear stress during the plastic deformation of specimen is caused by the competition between atoms which form new atomic planes and slip on different slip planes.