Study on Nano-scale Plastic Deformation of Alloy by Molecular Dynamics Simulation
| Autor: | LIU, BAO-HSIN, 劉寶信 |
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| Rok vydání: | 2016 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 104 The purpose of this study was to analyze the bonding characteristics and nano-structure of the metal alloy based on simulation of the principles of molecular dynamics. The simulation process consisted of three stages such as compressing, holding and stretching. The tooling system was divided into two upper and lower dies. During simulation process, the upper die was downward moved with a constant velocity to conduct compressing process. The alloys which were used in this study are Al-Cu, Al-Cu-Mg and Al-Cu-Mg-Fe. During the compressing process, a bonding interface which was called to be a film was generated at between two alloy layers. After simulation, the results were obtained, such as rupture of alloy, ultimate stress, interface position and area as well as formed force. From these results, they showed that for Al-Cu material in all forming processes, its interfacial area was crunched fast and withstood a greater forming force due to the ductility of material. Al-Cu-Mg have hard material structure, the compression speed of interfacial area is normal compared to the other. The less withstand interface force, and slower time to produce the maximum force is characteristic of Al-Cu-Mg. The reaction rate of Al-Cu-Mg-Fe is the fastest, and the interfacial area of Al-Cu-Mg-Fe is fast with the advantage of averagely speed. During the simulation process for a material block, the geometry of the material was changed from elastic to plastic deformation. After the yield point, it produced a slip phenomenon of multi-layers. Thus, it finally led to the plastic hardening and the fracture of materials due to ductile shear. Furthermore, the interfacial area became hardness and brittleness when the rapidly increased pressure. At slower compressing speeds, their atoms were diffused into the space of interfacial area and produced a high hardening during compression. Thus, the bonding interface had a better strength. When the stretching at a slower speed, the bonding interface of block was more slender. However, when rapidly increased speed, the internal atoms of the bonding interface caused a severe disturbance, and the condition of lattice distortion was shifted dislocation. Thus, the peak of stress appeared earlier and the bonding interface of the alloy can be fractured. Generally, the compressive process resulted in the nano-metal particles, which were a basis for the further study of the advanced nanometer wire extrusion technology. The extrusion technology was applied to make a niobium-titanium (Nb-Ti) alloy wire with the lattice structure and properties at the unit cell by the use of Material Studio software. The CAD software was used to design the geometry of extruded mold. LAMMPS was used to perform the simulation of alloy extrusion based on the multi-body molecular dynamics (EAM). This was the main software that was used to calculate the actions of potential energy and kinetic energy between the intermoleculars. Excel software was used to carry out the analysis of data, and then the VMD, as a post-processing, was used to produce a result of information graphics. Therefore, the pre-process, the main operational processes and the post-process were three simulation processes for the extrusion of the niobium titanium alloy wire at nano-scale. They can generate information of each time step, potential energy, formed load and displacement during the extrusion process. These results can be used for manufacture MEMS and semiconductor and can provide data for libraries. Furthermore, they can be used for the design of the sub-micron and nanometer extruded mold. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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