Young Tae Cho

A numerical analysis of a gas—tungsten arc welding considering the current density and temperature distribution on the electrode surface:

Abstract In numerical analysis of an arc plasma, the current density distribution and temperature distribution along the electrode surface are the most important boundary conditions, and a more accurate analysis can be achieved with a correct description of them. It was found that a distributed temperature condition taken from measured data makes isothermal contours broaden. The current density on the electrode surface was assumed to have a Gaussian distribution and its distribution parameters could be calculated for various electrode vertex angles. Analytically calculated distribution parameters helped the calculated temperature contours of the arc plasma to conform fairly well with experimental data.

Deposition and etching characteristic of magnetite thin film for absorptive wire grid polarizer with 45 nm line and space pattern

Magnetite, Fe3O4, is a mineral and one of three commonly naturally occurring oxides of iron. Small grains of magnetite exist in almost all igneous and metamorphic rocks. Most advance studies on magnetite films have focused on the characteristics of films by the growth of crystals such as nanowires. In this study, several processes of the magnetite film and patterning recipes are proposed. The authors deposited the Fe3O4 about 100u2009nm on the glass wafer using an e-beam evaporator. The 45u2009nm line/space pattern using nanoimprint process was made, and the residual layer could be reduced up to about 20u2009nm thickness. In addition, several possible etching gases and optimal conditions are suggested with proper etch selectivity.

An Analytical Study on the Residual Stress Generated by Seal Weld Repair of CEDM Nozzle in the Nuclear Power Plant

Abstract The reactor vessel closure head has many CEDM nozzles through which the control element drive mechanisms pass. The CEDM nozzle weld region of the reactor vessel closure head is composed of Alloy 600 material. It has been found that cracks occur due to the high stress generated during normal operation of the nuclear power plant and the contact environment with the primary cooling water. Seal Weld Repair blocks the environmental factor that may causes primary water stress corrosion cracking(PWSCC) by covering Alloy 600 weld region which is susceptible to PWSCC with Alloy 690 resistant to the stress corrosion cracking. In this study, a finite element analysis was performed to evaluate the effect of residual stress formation by seal weld repair in the nuclear power plant CEDM nozzle. The thickness of the welded structure and the number of welded layers were considered as variables. As a result, we showed that seal weld repair for J-groove weldment of CEDM nozzle can release the tensile residual stress so that the possibility of occurrence of PWSCC can be reduced. Also, it has shown that a multi-layer is more effective and thicker weld bead is more secured for reducing residual stresses in J-groove weld.

Multiscale Structures Aggregated by Imprinted Nanofibers for Functional Surfaces

Multiscale surface structures have attracted increasing interest owing to several potential applications in surface devices. However, an existing challenge in the field is the fabrication of hybrid micro-nano structures using a facile, cost-effective, and high-throughput method. To overcome these challenges, this paper proposes a protocol to fabricate multiscale structures using only an imprint process with an anodic aluminum oxide (AAO) filter and an evaporative self-aggregation process of nanofibers. Unlike previous attempts that have aimed to straighten nanofibers, we demonstrate a unique fabrication method for multiscale aggregated nanofibers with high aspect ratios. Furthermore, the surface morphology and wettability of these structures on various liquids were investigated to facilitate their use in multifunctional surfaces.

Fabrication of wire grid polarizer for spectroscopy application: From ultraviolet to terahertz

ABSTRACT Wire grid polarizer has high extinction ratio, brightness, excellent durability and large acceptance angle of light. The interest in grid-type polarizer has maintained continuously over recent decades since it can cover from ultraviolet to terahertz range. As nanotechnology advances, size, shape and material of wire grid can be controlled by various fabrication processes. A review of fabrication, materials, simulation schemes and new designs of wire grid polarizer is presented. Additionally, research trend of wire grid polarizers in terahertz time domain spectroscopy is addressed.

Analysis of Microstructure and Mechanical Properties According to Heat Treatment Conditions in GMAW for Al 6061-T6 Alloy

Recently, aluminum alloy has used various industry, such as automobile, shipbuilding and aircraft because of characteristics of low density and high corrosion resistance. Al 6061-T6 is heat treatment materials so it has high strength and mostly used for assembly by mechanical fastening such as a bolting and riveting. In GMA (Gas Metal Arc) welding of alloy, some defects which are hot cracking, porosity, low-mechanical properties and large heat affected zone is generated, because of high heat conductivity. It reduces mechanical properties. In this study, the major factor effected on properties are analyzed after welding in Al 6061-T6 in GMAW, then optimize heat treatment conditions. Plate of Al 6061-T6 with a thickness of 12 mm is welded in V groove and applied welding method is butt joint. Mechanical properties and microstructure are analyzed according to heat treatment condition. Tensile strength, microstructure and Hardness are evaluated. Result of research appears that Al 6061-T6 applied heat treatment show outstanding mechanical properties.

Refractive Index Variation of Fe3O4 Thin Film According to Deposition Rate

Recently, the display industry is focusing on making bendable or flexible displays with higher quality and larger area. Ultimately, there is a very high possibility that future displays will be rollable. The biggest problem with rollable displays is the fabrication of a polarizer film to prevent reflection of the OLED. To develop a rollable display, the display should be made of material with a very thin thickness, like that of paper. However, the thickness of the polarizer film used for displays is only approximately 180 μm. This means that the film is too thick to be applied to rollable displays. If a polarizer of wire grid type, which we investigate in this study, is used, it can reduce the thickness of this film to a value under approximately 1 μm. One research result has been to discover that Fe3O4 is a very slightly absorptive material. Especially, most research into Fe3O4 thin films has concentrated on its characteristics in nanotubes. So, our purpose in this research is to investigate the deposition process of Fe3O4 thin-film under various conditions using an E-beam evaporator; we intend to compare these various processes with each other after measuring the refractive index.

Determination of the Cutting Area Considering the Tool Slenderness Ratio for the Development of a 5-Axis Impeller Machining Automation CAM Module

The efficiency of applying 5-axis machining is higher for various products compared to general 3-axis machining, which is restricted to general parts and mold machining. However, impeller machining requires a large tool slenderness ratio to avoid interference with neighboring surfaces. Because such an enlargement of the slenderness ratio causes damage to the tools and deterioration of the quality of products due to the vibration of the tool, it is important to review the cutting characteristics considering the slenderness ratio and to determine the proper cutting conditions. Also, industry has attempted to develop a 5-axis machining automatic CAM module for an impeller that helps inexperienced workers to process the impeller easily by simplifying the process and options for the cutting impeller. The, current status of research on the cutting conditions considering the slenderness ratio to complete a database for a sub-module accounting for the cutting conditions among the components of an automatic CAM module is urgent. Therefore, the purpose of this work is to review the cutting characteristics that influence the cutting of aluminum alloy, the typical material of impeller parts, while also considering slenderness ratio to complete the 5-axis machining automatic CAM module of an impeller and to determine the available cutting area during the roughing and finishing operations.

Development of Post Processor for Five-Axis Machine of Non-Orthogonal Head Tilting Type

A five-axis machine can be developed with various mechanisms as it simply adds two axes to three coordinate axes. Therefore, five-axis machining utilizes post-processor for conversion to NC code, which the five-axis machine can read, with tool path CL data created by CAM depending on the mechanism of each device. This study introduces a post-processor program that tilts from axis B, of which the head is inclined at about 45 degrees, moves straight toward the X and Z axes, rotates the table from C, and then moves along axis Y. The post-processor mechanism was applied to the program after calculating the rotation angles and tilting angles using inverse kinematics and mapping the part coordinate system by machine coordinate system. Then, to evaluate the established post processor formula, it was verified twice. First, a tool path that was identical to that created by a commercial post-processor program, Post Works, was post-processed and comparably reviewed to, verify the performance of the proposed method. Secondly, a test specimen was manufactured by creating NC data from the developed post processor program. After manufacturing the test specimen, the compatibility was verified, suggesting the possibility to commercialize the five-axis machine and the post -processor program.