Multiscale Simulation Research On The Nanometric Cutting Process And Mechanical Properties Of Microstructure

The demands of microstructure are increasing with the rapid development of the aerospace industry, precision machinery and the semiconductor industry, which demand high levels of performance. The physical length scale is one of the main technology development bottlenecks of these industries. The shrinking of device dimensions not only can reduce manufacturing costs and the number of device energy consumers, but can also increase system functionality. Therefore, it is a key task to expedite discovery of the theory system of manufacturing and design for microstructure in the manufacturing industry field. In this thesis, multiscale simulation, which links the molecular dynamics (MD) and finite element (FE) methods, is employed to research the nanometric cutting mechanism and the tension fatigue property of microstructure. Meanwhile, the nano scratching experiments using a Hysitron TriboIndenter is performed to verify the results of simulations. This study has both theoretical and practical importance for a better understanding of the deformation mechanism, surface quality and the mechanical properties of microstructure, which will contribute to the design and manufacturing processes of microstructure.According to the analysis of the basic theory frame and related techniques of Quasicontinuum method, a parallel multiscale simulation model of nanometric cutting of single crystal copper is established. This multiscale model embodies the spanning scale character of materials deformation in ultra-precision machining and nanometric cutting processes, by which the computational cost is saved at the same time. The effect of orientations and cutting directions on chip formation, generation and evolution of defects, residual stress, cutting force and strain energy is investigated to have some invaluable insights, and the optimum machining direction in the nanometric process is ascertained. The multiscale simulation models of nanometric cutting single crystal copper microstructure with different machining process parameters are constructed. The impacts of cutting speed and cutting depth on the machining property and service performance of microstructure has been studied in various aspects, such as the deformation behavior, surface roughness, cutting forces, strain energies, defects on the machined surface and micro damaged layer. Thereafter, special deformation mechanism under the cutting condition of super high speeds and the impact of minimum cutting depth on the micro deformation mechanism in the nanometric machining process are studied. The simulation results indicate that there is not only tensile stress but also compression stress in the machined surface in the process of nanometric cutting. Meanwhile, the nano scratching experiments in different cutting depths are carried out. The results of the multiscale simulation are found inline to the results of nano scratching, which further confirms the accuracy of this technique. Compared simulation to experimental results and considered to the evolution law of defects and the distribution of residual stress, a material removal mechanism involving extrusion-scratching is proposed.On the other hand, the multiscale simulation models of uniaxial tension and compression deformation for single crystal copper microstructure with different V-notches has also been developed to study the influences of orientations and V-notch types on the properties of tension fatigue for microstructures in various aspects, such as the generation and evolvement of defects, fatigue pattern of notch, tension-compression loads and strain energies. It is found that orientations and notch types have a significant impact on the micro deformation mechanism of microstructure. During the processes of tension-compression, there are new bonds formed in notch tip when the microstructures are under tensile stress while the atomistic bonds break from new atomistic plane when the microstructures are compressed. This type of deformed mechanism determines the property of microstructures subjected to cyclic loads. To analyze and characterize the mechanical properties of microstructure based on multiscale simulation model will contribute to the fundamental theory of design and manufacture of microstructure for its further development.