Simulation On Nanometric Cutting Based On Quasicontinuum Mutilscale Method

Nanocutting is the effective method to obtain optical surface with high precision.When cutting thickness spans from micron grade to the nanometer level, the cuttingprocess is not only a qualitative change but also a quantitative change process. Thephenomenon of nanocutting is discrete and discontinuous. So the traditionalcontinuous method, such as the finite element, is not suitable to investigate themechanism. With the development of computer, molecular dynamic is the mainmethod to study the nanocutting mechanism. However, the length and time scales thatit can deal with is also limited. And the simulation accuracy is limited by settingboundary condition in molecular dynamics. So it is important to study the multiscalemethod. The quasicontinuum method is one of the multiscale method, achieving thegoal of linking the atomistic to continuum body by the use of Cauchy-Born rule.Moreover the size expand without losing accuracy.The targets of this paper are studying the single copper nanocutting process bymeans of quasicontinuum method and to investigate new nanocutting simulationapproach. The contents of this paper are:(1) Through contrast experiment to study various types of multiscale method, inorder to choose the optimization method that is suit to study nanocutting. For thequasicontinuum method, including the bridging domain (BD), coupled atomisticsand discrete dislocation(CADD) method, the shear deformation experiment of singlecrystal aluminum with dipole dislocation was conducted. It is found that the loadcurve and atomic displacement of the QC are close to the exact atomistic approach.In addition, the QC is the fastest among the three multiscale method,moreoverimprove efficiency near80%. So QC method is selected in this paper.(2) In this study, combined with the characteristics of nanocutting, the multiscalenanocutting simulation platform is build written by FORTRN language. Theprogram of nanocutting quasicontinuum simulation includes five parts. Theuser-mesh subroutine is used to dived mesh; user-bcon is used to set boundarycondition, use-potential is to read the potential and user-pdel is applied lode,user-plot is to output parameter, respectively. The shape of the tool is circle withmore close to nanocutting experiment and the size of the workpiece is 100nm×200nm.(3) With the single copper as the workpiece to explore the effectiveness of QCplatform to study the nanocutting process. The surface formation and the change ofcutting force and specific cutting energy with the cutting depth change. The resultshow that the surface is formed by tool crushed on the workpiece. With increase ofcutting depth, cutting force is increased and cutting specific energy is decreasedbecause the atom number is increase and the volume of the material to remove islarger. The effect of crystal orientations on nanocutting is done. The result shownthat when cutting [10(?)] on (111), the dislocation is parallel to the cutting direction,the deformed layer is thinnest. And the residual stress is lowest, the surface qualityis better. It proved that the QC is an efficient multiscale approach to studynanocutting mechanism.