Molecular Dynamics Study Of Nanomechanical Propetries Of Machining-involved Surface On Crystalline Copper

As one of the frontiers in modern manufacturing technology, ultra-precisionmachining makes the manufacture and application of devices with shape anddimensional accuracy in nanoscale possible. When the specimen’s dimension reachesnanoscale, the surface effect, quantum effect and size effect become noticeable. Thedeformation and removal mechanism of materials also become obviously differentfrom those of traditional mechanical machining. Such a difference between theultra-precision machining and traditional machining indicates that the classic theorybased on continuous medium mechanics theory is no longer applicable inultra-precision machining. Therefore, the method based on discrete mediummechanics theory is adopted for explaining and revealing the phenomenon andmechanism of ultra-precision machining in nanoscale.In ultra-precision machining studies, researchers home and abroad have achievedamounts of accomplishment by adopting ultra-precision machining on the crystallinecopper surface and researching the material removal mechanism. However, there isless research on the nanomechanical properties of machining-involved surface.Because of differences on micro structure and energy state betweenmachining-involved surface and crystalline surface, there is a change in the materialdeformation and removal mechanism. Therefore, focusing on the above problems,molecular dynamic simulations are applied to research the deformation and removalmechanism in the ultra-precision machining. Simulations of nanoidentation andnanoscratching are conducted and the properties of machining-involved surface areobtained. According to the simulation results, damage accumulation in materials afterseveral ultra-precision machining is employed. Details of the research include thefollowing:First, this article builds up a three-dimensional molecular dynamics model ofultra-precision machining and nanoidentation on crystalline copper. Then, it studiesthe deformation mechanism on the crystalline copper surface in ultra-precisionmachining. The nanoidentation test is conducted on the machining-involving surface.The kinds and distributions of defects in the material are identified and analyzed,based on crystal plasticity theory and analysis technique of crystal defects. The article explains the mechanism of nanoidentation on the machining-involved surface and thephysical parameters of the machining-involved surface are measured, such as surfacehardness and elastic modulus. The article also explains the mechanism of surfacesoftening effect on machining-involved surface. Besides, the simulation also revealsthe deformation mechanism along different crystal orientation in ultra-precisionmachining process. Quantitative researches of the machined-involved surfaces areconducted with the help of nanoindentation and the relation between cutting force,surface damage and softening degree becomes clear.For further studies on mechanical properties of machining-involved surface,molecular dynamic models of ultra-precision machining and nanoscratching tests areemployed. By analyzing the damage and deformation in the specimen duringnanoscratching on machining-involved surface, and comparing it with that on thecrystalline copper surface, we clearly define the influence of residual damage towardsthe dislocation nucleation in nanoscratching, and the influence of slip towards surfacemechanical properties. Calculation of friction coefficient at different depths on theultra-precision machining-involved surface is carried out. Under varied geometricalparameters of tools, with the nanoscraching, measurements of damage degrees onmachining-involved surface in ultra-precision of nanoscale are accomplished.According to the studies on mechanical properties of machining-involved surfacein this article, further investigation is carried out. Repeated cuttings are conducted onthe machining-involved surface, which makes the deformation and damagemechanism of machining-involved surface clear. Then we get nanomechanicparameters of machining-involved surfaces under different cutting times. Combiningtheories of friction abrasion and crystal elasticity, a predicting method of surfacedamage accumulation and surface potential based on nanoidentation are come out.This prediction method works well in qualitative description and prediction of surfacehardness and potential energy of machining-involved surfaces, thus providing atheoretical explanation of ultra-precision machining mechanism in nanoscale.Overall, the investigation in this article is not only an extension explanation ofultra-precision machining, but also an exploration of prediction theory inmachining-involved surfaces formation and mechanical properties. Investigations andanalysis of machining-involved surfaces mechanical properties after ultra-precisionmachining provide theoretical basis of ultra-precision machining technique for further research and develop a new researching approach.