Research On Mechanism Of Nano-Machining Single Crystal Silicon And Influcencing Actors By Molecualr Dynamics

The development of nanometric machining technology makes it possible of manufacturing nano-electromachanical system manufacture. When dimension of the microstructure reaches nanometer scales, nano-masnufacturing theory and method are essentially different from traditional mechanical design and method because mechanical properties, load characteristics and failure mechanism will change intrinsically in such dimensional scale.Therefore, traditional mechanical design theory and method based on classical continuum mechanics can not be applied directly to nanometric machininig technology, and new research method should apply ideas from latest progresses in modern physics to study nano-manufacturing mechanism from the atomic-scale point of view. In this thesis, molecular dynamics (MD) simulation is employed to investigate the deforming mechanism of single crystal silicon planes during nano-indentation and scratching process and relative experiments are carried out. Then the nano-cutting mechanism of brittle material single crystal silicon and researches of diamond tool wear and its effect on cutting process are discussed. The fulfillment of this study has resulted in a better understanding of the nano-manufacturing mechanism of single crystal silicon, and it is of significance for theoretical instruction of practical design and nano-manufacturing processes. Therefore, it will contribute to the fundamental theory of nano-manufacturing for their further development.Firstly, the three dimension simulation models of nano-indentation and scratching of single crystal planes (100), (110) and (111) are set up to make researches on nano-deforming mechanism and micro mechanical properties. At the same time, experiments related to simulation models are carried out. The experimental resulats show that the elastic modulus value of (111) plane is smaller than that of (100) and (110) planes, and the relationship of elastic modulus of the three classical planes is corresponding to that of simulation. For the three planes, the relationship of increasing slopes of scratching loads along with scratching depths is corresponding to that from the experiments.The phenomena mentioned above indirectly prove that MD is effective method to research silicon nano-machining process, and that relative basic theories about building models are right.Secondly, nano-cutting mechanism is studied through analyzing atomic temporal map, structural variation of deforming areas, the development of work piece potential, cutting force and so on, and anisotropic influences on cutting process are studied, also. The simulation results shows that single crystal structure phase change is progressive without dislocations during nano-cutting process according to change process of potential and cutting force; there are differences of potentials in chip area of the three crystal planes; the expanding velocity of deformed area near tool's rake face is in the same order with cutting speed; on machine surface altitude root mean square deviation is in order of 0.01 nm; stress is in order of 0.01 GPa and there are differences in stress values due to different crystal planes.Finally, diamond tool wear during single crystal silicon nano-cutting is studied, and the effect of temperature viriation on tool wear is researched through building cutting model. According to atomic temporal map, some outdoor atoms of tool are moved in the initial phase of cutting, and then degree of tool wear is reduced obviously in the following cutting process. There are different phase structures formed in the tool during cutting process and the phase structures are analyzed by radial distribution functions. There is an increase of atomic density in subsurface of tool which prevents tool from further wear. Average atomic potentials of tool's top surface and sub-surface are added with increase of system temperature while the cutting force is lessened. The activity of silicon atoms is raised remarkably due to increase of temperature than that of tool atoms so that the cutting process can be continued steadily.