Jia Xuan Chen

Mechanism of Material Removal and the Generation of Defects by MD Analysis in Three-Dimensional Simulation in Abrasive Processes

Molecular dynamics (MD) simulations of nanometric scratching with diamond tip are conducted on single crystal copper crystal plane (010), and MD simulations are carried out to investigate the mechanism of material removal and the generation of defects on the surface, subsurface and inner of material. During the process of diamond tip scratching the surface of single crystal copper on conditions of different scratching speeds, depths and widths. We achieved the forming details of the chip. While the generation and moving process of defects, such as dislocation, are recorded. The different times of atomic displacement and interaction force are also shown through MD simulation. The evolvement of the lattice pattern in the abrasive processes are analysed by radial distribution function (RDF) and computing the changes of workpiece’s atomic displaces and forces. At the same time, the lattice reconfiguration and the onset and the evolvement process of defects and are analysed by RDF and atomic perspective method, respectively. The simulation results show that scratching speed play role in the course of the form of removing chips, and that different scratching widths and depths of tool have effect on onset and evolvement of lattice defects of workpiece in abrasive processes. This study can give more fundamental understanding of nanosconstruction from atomistic motions and contribute to the design, manufacture and manipulation of nano-devices

Potential Analysis in Nanoturning of Single Crystal Silicon Using Molecular Dynamics

Molecular dynamics simulations of the single crystal silicon nanoscale cutting with a diamond tool in ductile mode are carried out to investigate the adhesion phenomenon. After relaxation the silicon atoms on the surface reconstruct to make the potential decrease. The silicon atoms close to the diamond tool have the lowest potential (<-5.5 eV) and form a stable structure with surface atoms on the tool surface.

Monte Carlo Simulation and Applications in Design and Manufacture of Nanostructures

This paper provides a review of Monte Carlo (MC) method and its applications in mechanical engineering. MC simulation is a class of computational algorithms which require repeated random sampling and statistical analysis to calculate the results. The basic principles, formulas and recent development of Monte Carlo method are firstly discussed briefly, and then the applications of MC simulations in the design and manufacturing of nanostructures are reviewed. Finally, we briefly introduce MC simulation of morphology evolution of machined surface, which come from our recent work.

MD Simulation of Nanocutting Process: Removal Mechanism, Defects Evolvement and Characterization

Three-dimensional molecular dynamics simulation of AFM diamond tip nanoscratching on the (100), (110), (111) crystal faces of single-crystal copper were performed to research the effect on the nanocutting process. The evolvements of subsurface defects are analyzed under different orientation and cutting depth. The results show that the regulations of defects evolvement in different orientation are different in nanocutting process. When AFM diamond tip scratches the (111) orientation of single-crystal copper, there exists dislocation which nucleates beneath the tool and propagates downwards along the (1-11) slide plane. With the decreasing cutting depths, the cutting force peak and averaged cutting force decrease; the cutting force of (111) orientation is biggest, and that of (110) orientation is lowest.

Simulation Study of Material Deformation in Monocrystal Silicon Nano-Machining

Molecular dynamics simulations method is used on the study of material deformation in monocrystal silicon during nanomachining. Both nanoindentation and nanocutting by a diamond tool tip is investigated using LAMMPS. Characterization methods such as coordination number and labeling atoms in different layers have been adopted to study the law of transformation. As the surface atoms are tracked, their transformation law is analyzed and the formation mechanism of the cuttings and finished surface is announced. The impact crystal orientation of silicon on the machining is also studied.

Frequency Domain Error Analysis in Ultra-Precision Flycutting

In some special fields such as precision optics, the part surface has strict requirements on the frequency domain errors, besides the conventional spatial domain errors such as surface roughness error. In light of the available works lacking of the frequency domain error analysis in ultra-precision flycutting, this paper therefore presents its frequency domain error analysis. A case study of KDP crystal flycutting is carried out to show its detailed processes, where the processing parameters, tool geometry, motion dynamic error of the machine guideway and tool-work vibration induced dynamic error are considered. A surface profile generation method is put forward. Two cases with different tool-work vibration frequencies are carried out. The spatial frequency spectrum is obtained based on the FFT analysis of the generated profile in the specified direction. After the in-depth analysis, the inherent correlation of the generated spatial frequency components with feed spatial frequency and machine dynamic errors induced spatial frequency under certain machining conditions are found, which is very meaningful for the frequency domain error prediction in the real application. The proposed analysis method can also be applied into other types of surface machining.

Molecular Dynamics Simulation Research in Water Adsorption on Aluminum Surface

In this paper, molecular dynamics method was used in researching the adsorption between single crystal aluminum and water, we built a molecular dynamics model of single crystal aluminum and water, researched the adsorption state of water on the surface of single crystal metal aluminum after nanofabrication, and gained the simulation value of the surface contact angle between aluminum and water. We also studied the impact of different orientations, different surface nanostructures, and different system temperatures on the surface contact angle. The simulation results show that: for single crystal aluminum of [10 crystal plane and water, when happen adsorption, the contact angle is approximately 61.5°, the same with the measured results; and for [11 single crystal aluminum, the contact angle is approximately 70.5 °, so different arrangement of crystal orientation has affect on surface contact angle, but does not change the hydrophilic nature. When the trench depth of the aluminum crystal surface increases, the surface contact angle is gradually increasing; and when the temperature rises, the surface contact angle increases to a certain extent.

Ageing Effect on Mechanical Properties of Machined Nanostructures

Monte Carlo (MC) method and molecular dynamics (MD) are combined to analyze the influence of ageing on mechanical properties of machined nanostructures. Single crystal copper workpiece is first cut in MD simulation, and then the machined workpiece is used in MC simulation of ageing process, finally the tensile mechanical properties of machined nanostructures before and after ageing are investigated by MD simulation. The results show that machining process and ageing have obvious influence of tensile mechanical properties. After machining, the yield strength, yield strain, fracture strain and elastic modulus reduce by 36.02%, 28.86%, 20.79% and 7.16% respectively. However, the yield strength, yield strain and elastic modulus increase by 4.84%, 1.41% and 1.02% respectively, fracture strain reduce by 24.53% after ageing process. To research the ageing processes of machined nanostructures by MC simulation is both practical and meaningful.

Influence of Ageing on Surface Quality of Machined Nanostructures

A three-dimensional model of Monte Carlo (MC) simulation is proposed to study the effects of ageing on the surface quality of machined nanostructures. The model includes the utilization of the Morse potential function to simulate the interatomic force between the atoms in workpieces. The results show that the ageing processes have important influence on the surface morphology and internal structure of machined workpiece. Most of the disordered point defects and one large stacking fault structures in machined workpiece disappear after ageing, but still some defect structures remain. In addition, distribution of atomic potential and atomic stress in the workpiece become regular in the aging process, and the atoms of the defect structures have much higher potential energy and stress. Finally, surface roughness of machined workpiece definitely increases after ageing. To analyze the morphology of machined surface after ageing is very practical and meaningful.

Adhesion of Silicon to the Tool during Diamond Cutting Silicon by Molecular Dynamics

Wear of diamond tool is also very serious, which affects the surface quality of the machined work material, even if ductile mode where an undeformed chip thickness is at a nanoscale is used. During the cutting process, the crystal structure in the cutting zone is destroyed under the high pressures applied by the diamond tool. The silicon atoms adhering to the tool surface reconstruct to be in a crystal state under the effect of adhesion and pressures.