Molecular Dynamics Simulation Of Nanoindentation And Ultra-precision Machining

Ultra-Precision Machining(UPM) is an advanced processing technology, with the depth of cut on nano-scale and discreteness the dominant factor in the UPM. The constitutive model based on continuum mechanics is not suitable for characterizing the ultra-precision machining processes. Molecular Dynamics(MD), which finds a wide application in nano-mechanics in recent years, can successfully shed light on the mechanical behaviors of nanoindentation and UPM processes.By using LAMMPS, a Large-scale Atomic/Molecular Massively Parallel Simulator,simulations of nanoindentation and UPM are carried out, the results obtained are as follows:I. Simulation of nanoindentation is conducted using single-crystal copper as workpiece to investigate the effect of crystal orientation on nano-hardness. A reliable and efficient algorithm for calculating the projected contact area is proposed. The calculated indentation hardness demonstrates clearly size effect. The dislocation extraction algorithm is adopted to extract dislocation lines with the results showing multiple evolution mechanisms of dislocations, such as dislocation nucleation, multipication and annihilation.II. Conclusion can be drawn based on simulation of nanoindentation on polycrystal copper that in some cases the bigger the grain size is, the larger the force between indenter and workpiece and thus the higher indentation hardness, demonstrating the inverse HallPetch(H-P) effect.III. Simulation of UPM processes is performed on single crystal copper to investigate the effect of crystal orientation and depth of cut on the cutting and thrusting forces. The scratching hardness is also calculated by using the ratio between the cutting force and the projected contact area perpendicular to the cutting direction.