63 results on '"Byoung-Soo Lee"'
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2. Effect of career identity on Taekwondo Poomsae and Demonstration Team university students’ intention to continue exercise and Intention to change career path
- Author
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Byoung-Soo Lee and Byung-Kwan Lee
- Published
- 2022
3. Effect of Preheating Temperature on Microstructural and Mechanical Properties of Inconel 718 Fabricated by Selective Laser Melting
- Author
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Jung-Hyun Park, Gyung Bae Bang, Kee-Ahn Lee, Yong Son, Yeong Hwan Song, Byoung-Soo Lee, Won Rae Kim, and Hyung Giun Kim
- Subjects
Mechanics of Materials ,Materials Chemistry ,Metals and Alloys ,Condensed Matter Physics - Published
- 2022
4. Microstructure Formation Mechanisms of Spinodal Fe–Cu Alloys Fabricated Using Electron-Beam Powder Bed Fusion
- Author
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Haejin Lee, Minhyung Cho, Minho Choi, Yeonghwan Song, Kwangchoon Lee, and Byoung-Soo Lee
- Published
- 2023
5. Microstructure Formation Mechanisms of Spinodal Fe–Cu Alloys Fabricated Using Electron-Beam Powder Bed Fusion
- Author
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Haejin Lee, Minhyung Cho, Minho Choi, Yeonghwan Song, Seung-Min Yang, Hyung Giun Kim, Gunhee Kim, Kyunghoon Kim, Kwangchoon Lee, and Byoung-Soo Lee
- Published
- 2023
6. The Effects of Career Awareness in Taekwondo Field on Intrinsic and Extrinsic Satisfaction of Taekwondo Activities: Focused on Poomsae and Demonstration Team University Students
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Byung-Kwan Lee and Byoung-soo Lee
- Subjects
General Medicine - Published
- 2021
7. The Effect of their Social Face Sensitivity by Camping Goods Consumers on Luxury Brand Preference and Luxury Brand Purchase Intention
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Byung-Kwan Lee and Byoung-Soo Lee
- Subjects
Brand preference ,Face (sociological concept) ,Statistical analysis ,Advertising ,Business ,Affect (psychology) ,Preference ,Confirmatory factor analysis ,Purchasing ,Structural equation modeling - Abstract
The purpose of this study was to structurally identify the influence of face-sensitive consumers on camping equipment"s preference for luxury goods and intention to purchase luxury goods. The subjects of the study were campers with experience in camping activities and purchasing camping equipment, and 204 people were used for the final statistical analysis. Statistical analysis was conducted as a confirmatory factor analysis and a structural equation model analysis, and the results were as follows: First, it has been shown that the face sensitivity of consumers of camping equipment does not affect the preference of luxury goods. Second, it has been shown that consumers" sensitivity to face of camping equipment does not affect their intention to purchase luxury goods. Third, consumers" preference for luxury goods in camping equipment has a positive effect on their intention to purchase luxury goods. These results can be interpreted as that consumers of camping equipment prefer or do not purchase luxury equipment due to their face sensitivity, but consumers who tend to prefer luxury goods are more likely to purchase luxury goods.
- Published
- 2021
8. Microstructural study on a Fe-10Cu alloy fabricated by selective laser melting for defect-free process optimization based on the energy density
- Author
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Seung-Min Yang, Kwangchoon Lee, Jung Hyun Park, Hyung Giun Kim, Taeg Woo Lee, Won Rae Kim, Gyung Bae Bang, Gun-Hee Kim, and Byoung-Soo Lee
- Subjects
lcsh:TN1-997 ,Materials science ,Alloy ,02 engineering and technology ,engineering.material ,01 natural sciences ,Biomaterials ,Energy density ,0103 physical sciences ,Process optimization ,Laser power scaling ,Composite material ,Selective laser melting ,lcsh:Mining engineering. Metallurgy ,Shrinkage ,010302 applied physics ,Fusion ,Range (particle radiation) ,Metals and Alloys ,Fe-10Cu alloy ,021001 nanoscience & nanotechnology ,Surfaces, Coatings and Films ,High density ,Scientific method ,Ceramics and Composites ,engineering ,Defect ,0210 nano-technology - Abstract
Process optimization for the selective laser melting (SLM) of the Fe-10Cu alloy was performed to obtain defect-free parts based on the energy density for thermodynamically complete melting. A microstructural study was conducted for the corresponding energy densities that focused on identifying defect formation mechanisms. A range of defects formed via by diverse mechanisms, such as lack of fusion, balling, shrinkage and the key-hole effect, were characterized, including mixed zones. The process range in which these defects were not formed could be suggested as the optimal conditions for SLM of the Fe-10Cu alloy. In this study, a laser power below 320 W, a scan speed below 1523 mm/s and an energy density under 15.56 J/mm3 were indicated to be the optimum process conditions for SLM of Fe-10Cu alloy to avoid micro-cracks from shrinkage, balling and rounded pores from the key-hole phenomenon.
- Published
- 2020
9. Effect of electron beam continuity on microstructures and mechanical properties of titanium lattice structures produced with electron beam additive manufacturing
- Author
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Byoung-Soo Lee, Seok-Joon Jeong, and Hae-Jin Lee
- Subjects
Electron-beam additive manufacturing ,Materials science ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Commercially pure titanium ,FeTi4 phases ,Phase (matter) ,General Materials Science ,Composite material ,Porosity ,Elastic modulus ,Materials of engineering and construction. Mechanics of materials ,Mechanical Engineering ,Electron-beam continuity ,021001 nanoscience & nanotechnology ,Microstructure ,0104 chemical sciences ,Compressive strength ,chemistry ,Mechanics of Materials ,Lattice structures ,TA401-492 ,Grain boundary ,0210 nano-technology ,Titanium - Abstract
The effects of the electron beam (EB) continuity on the microstructures and mechanical properties of titanium lattice structures with produced by EB additive manufacturing were studied. Continuous line and discontinuous spot scans were applied for the EB continuity. The porous structures produced with the continuous line scans had lower defect densities than those produced with discontinuous spot scans. Most defects of the continuous line scans had spherical morphologies, whereas non-spherical defects formed in the porous structure produced with discontinuous spot scans because of the availability of sufficient heat for melting the powder. The microstructures were composed of an α-titanium matrix, martensitic α′ phases, and elongated FeTi4 phases on the grain boundaries. Furthermore, the atom probe tomography results showed that the FeTi4 phase had a network structure with a diameter of 5 nm after the continuous line scan, which enhanced the compressive strength. The compressive strength and elastic modulus of the porous structures produced with the continuous line scan were more than 400 MPa and 11 GPa, respectively. Despite the high porosity, continuous line scans are preferable for achieving high compressive strengths with low elastic moduli for biomedical devices.
- Published
- 2021
10. Effect of cyclic heat treatment on commercially pure titanium part fabricated by electron beam additive manufacturing
- Author
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Byoung-Soo Lee, Hyung Giun Kim, Tae-Wook Na, Hyung-Ki Park, Gun-Hee Kim, Jong Min Park, and Yanghoo Kim
- Subjects
Yield (engineering) ,Materials science ,Electron-beam additive manufacturing ,Mechanical Engineering ,Metals and Alloys ,Nucleation ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,Grain size ,0104 chemical sciences ,Mechanics of Materials ,Martensite ,Ultimate tensile strength ,Materials Chemistry ,Composite material ,0210 nano-technology ,Elastic modulus - Abstract
To improve the reliability and functionality of medical commercially pure titanium (CP-Ti) part fabricated by electron beam additive manufacturing (EBAM), we studied a post-treatment like cyclic heat treatment. For uniform microstructure by inducing the repetitive nucleation during phase transformation, the specimens were repeatedly heat-treated from 25 °C to 1,000 °C in Ar atmosphere. Microstructural and mechanical studies were carried out with as-built specimen and heat-treated specimens for 1, 3, and 5 cycles. Grain size was uniformly refined from 61.2 μm to 19.4 μm, in addition the elastic modulus was lowered from 136.8 GPa to 64.4 GPa. Particularly, the martensitic α′′ phase with orthorhombic structure in few tens of nm size was observed after cyclic heat treatment which was considered to reduce the elastic modulus. Although the yield and tensile strengths were slightly decreased after cyclic heat treatment, it was still higher value compared with the wrought CP-Ti part. For the patient-specific CP-Ti part, consequently, the cyclic heat treatment could be considerable post-process without any mechanical process.
- Published
- 2019
11. Influence of the focus offset on the defects, microstructure, and mechanical properties of an Inconel 718 superalloy fabricated by electron beam additive manufacturing
- Author
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Han-Kyu Kim, Hae-Jin Lee, Byoung-Soo Lee, and Hyun-Uk Hong
- Subjects
Materials science ,Electron-beam additive manufacturing ,Mechanical Engineering ,Metals and Alloys ,02 engineering and technology ,Intergranular corrosion ,Atmospheric temperature range ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,0104 chemical sciences ,Superalloy ,Thermal conductivity ,Mechanics of Materials ,Ultimate tensile strength ,Materials Chemistry ,Composite material ,0210 nano-technology ,Inconel - Abstract
The defects, microstructure, and mechanical properties of Inconel 718 superalloy fabricated by electron beam additive manufacturing with different focus offsets were investigated. The samples built with a low focus offset exhibited numerous micro-voids of 10 μm and a columnar grain microstructure with a strong [001] texture in the built direction (BD). Unmelted powder and macro-voids of approximately 200 μm were observed at higher focus offsets, and the columnar grain width decreased from 600 μm to 150 μm with increasing focus offset. γ׳ precipitates with a length of 10 nm developed parallel to the BD, while γ״ precipitates with length of 4 nm formed perpendicular to the BD owing to the higher thermal conductivity. Samples built with a low focus offset exhibited intergranular fractures, while samples built with a high focus offset exhibited brittle fractures because of the unmelted powder and macro-voids. Samples built with focus offsets of 9 mA and 12 mA exhibited the highest tensile strengths of 1.3 GPa and 1.0 GPa at room temperature and high temperature, respectively. γ׳/γ״/γ׳ and γ׳/γ״/γ׳/γ״/γ׳ sandwich structures on the columnar γ grains developed parallel to the BD in the as-built samples because the preheating process between consecutive layers increases the dwelling time in the temperature range facilitating the δ → γ״ and δ → γ׳ phase transformation. The volume fractions and size of the γ׳ and γ״ precipitates increase with the focus offset owing to the prolonged dwelling time; however, micro-voids formed and unmelted powder was present because of insufficient heat of fusion.
- Published
- 2019
12. Alloy design of Ni-based superalloy with high γ′ volume fraction suitable for additive manufacturing and its deformation behavior
- Author
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Ji-Un Park, Sun-Young Jun, Bong Ho Lee, Jae Hoon Jang, Byoung-Soo Lee, Hae-Jin Lee, Je-Hyun Lee, and Hyun-Uk Hong
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Biomedical Engineering ,General Materials Science ,Engineering (miscellaneous) ,Industrial and Manufacturing Engineering - Published
- 2022
13. Publisher Correction: Graphene Oxide Quantum Dots Derived from Coal for Bioimaging: Facile and Green Approach
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Sungwook Mhin, Byoung-Soo Lee, Yong Son, Kang Min Kim, Jeong Ho Ryu, Kwang Bo Shim, Kyung-Hwan Jung, Suk Hyun Kang, Taeseup Song, and HyukSu Han
- Subjects
Multidisciplinary ,Materials science ,Graphene ,business.industry ,lcsh:R ,Oxide ,lcsh:Medicine ,Nanotechnology ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Quantum dot ,lcsh:Q ,Coal ,lcsh:Science ,business - Abstract
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
- Published
- 2020
14. Improvement of mechanical properties of cast pure titanium by repeated heat treatment
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Byoung-Soo Lee, Hyung Giun Kim, Jae Hyun Jung, Tae-Wook Na, Hyung-Ki Park, and Jaeho Choi
- Subjects
010302 applied physics ,Materials science ,Mechanical Engineering ,Metallurgy ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Microstructure ,01 natural sciences ,Grain size ,chemistry ,Mechanics of Materials ,Casting (metalworking) ,0103 physical sciences ,Mechanical strength ,General Materials Science ,0210 nano-technology ,Titanium ,Refining (metallurgy) - Abstract
Pure titanium components fabricated by casting have a coarse grain microstructure. To improve the mechanical strength of pure titanium components by refining the grain size, the cast samples were r...
- Published
- 2018
15. Thermodynamic analysis of oxygen refining during electron-beam additive manufacturing of pure titanium products
- Author
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Hyung-Ki Park, Tae-Wook Na, Byoung-Soo Lee, Hyung Giun Kim, Seung-Min Yang, and Gun-Hee Kim
- Subjects
Electron-beam additive manufacturing ,Materials science ,Mechanical Engineering ,technology, industry, and agriculture ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,Partial pressure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Oxygen ,0104 chemical sciences ,chemistry.chemical_compound ,Chemical engineering ,chemistry ,Mechanics of Materials ,General Materials Science ,Limiting oxygen concentration ,0210 nano-technology ,Chemical composition ,Titanium ,Refining (metallurgy) - Abstract
Chemical composition of pure titanium, particularly oxygen, severely affects mechanical properties of product. Oxygen refining during electron-beam additive manufacturing (EBAM) of pure titanium products was thermodynamically analyzed. The oxygen concentration of the titanium sample fabricated by EBAM was 0.172%, which was lower than that of the initial titanium powders (0.228%). This was mainly because the TiO2 native oxide layer formed on the initial powders reduced during EBAM, thereby decreasing the oxygen concentration. Analysis of temperature and oxygen partial pressure in the EBAM building chamber confirmed the occurrence of reduction and hence the oxygen refining effect.
- Published
- 2019
16. Mechanical Properties Including Fatigue of CP Ti and Ti-6Al-4V Alloys Fabricated by EBM Additive Manufacturing Method
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Young Sin Choi, Chang-Woo Lee, Byoung Soo Lee, Gun-Hee Kim, Dong-Geun Lee, and Chang Lim Kim
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010302 applied physics ,Materials science ,0103 physical sciences ,Metallurgy ,02 engineering and technology ,General Medicine ,Ti 6al 4v ,021001 nanoscience & nanotechnology ,0210 nano-technology ,01 natural sciences - Abstract
The Electron Beam Melted (EBM) method is one of the attractive attention thing additive manufacturing methods. By using an EBM additive manufacturing method, CP Ti and Ti-6Al-4V specimen were fabricated with a certain processing parameters. The mechanical properties such as fatigue limit, tensile properties including microstructural characteristics of CP Ti and Ti-6Al-4V specimens fabricated by EBM were confirmed and were compared with the conventional Ti alloys. Additive manufacturing was obtained high strength by creating martensite due to rapid cooling. On the other hand, void occurrence cannot be avoided by the method of using powder, accordingly it had a low fatigue strength value. Therefore, this study focused on that the values of fatigue characteristics of the EBM specimens and conventional specimens were compared and analyzed. EBM CP Ti had good mechanical properties such as yield strength, ultimate tensile strength, elongation and fatigue limits, approximately as same as casting CP Ti. EBM Ti-6Al-4V showed good mechanical properties, but fatigue limits were lower than wroughtTi-6Al-4V. That resulted from the formation of several kinds of internal pores which caused to increase the crack initiation and propagation.
- Published
- 2017
17. Study on surface shape control of pure Ti fabricated by electron beam melting using electrolytic polishing
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Hyung-Ki Park, Hyung Giun Kim, Jae Hyun Jung, Hyo Kyu Kim, Gun-Hee Kim, Bosung Seo, Jaeho Choi, and Byoung Soo Lee
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Surface (mathematics) ,0209 industrial biotechnology ,Materials science ,Metallurgy ,Polishing ,chemistry.chemical_element ,02 engineering and technology ,Surfaces and Interfaces ,General Chemistry ,Electrolyte ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Surface shape ,Flattening ,Surfaces, Coatings and Films ,Catalysis ,020901 industrial engineering & automation ,chemistry ,Materials Chemistry ,Cathode ray ,0210 nano-technology ,Titanium - Abstract
Titanium parts in special industries such as vacuum, catalyst and medical application require a variety of surface properties with a unique structure for high efficiency. In this study, the unique surface of commercially pure titanium (CP Ti) parts fabricated using Electron Beam Melting (EBM) in the process of additive manufacturing is post-treated by the electrolytic polishing process under conditions ranging from 10 to 30 V and 10–600 s in order to study the surface characteristics. The possibility of controlling microstructural surface shape according to electrolytic polishing process conditions is presented from the increase of surface area through the formation of micro-dimples on protruding residual powder on the surface to the flattening of entire surface.
- Published
- 2017
18. Histological Evaluation of Osseointegration of 3D Printed Ti6Al4V Screws
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Hae-Jin Lee, Eunjeong Cho, Byoung-Soo Lee, Rayun Choi, Kang-Sik Lee, and Hyewon Kim
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3d printed ,Materials science ,business.industry ,Dentistry ,business ,Osseointegration - Published
- 2019
19. Laser wavelength modulated pulsed laser ablation for selective and efficient production of graphene quantum dots
- Author
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HyukSu Han, Jeong Ho Ryu, Kyung Hwan Jung, Kwang Bo Shim, Kang Min Kim, Suk Hyun Kang, and Byoung-Soo Lee
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Photoluminescence ,Materials science ,business.industry ,Graphene ,General Chemical Engineering ,Oxide ,Coulomb explosion ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,0104 chemical sciences ,Nanomaterials ,law.invention ,chemistry.chemical_compound ,Wavelength ,chemistry ,Quantum dot ,law ,Optoelectronics ,0210 nano-technology ,business - Abstract
Graphene quantum dots (GQDs) and graphene oxide quantum dots (GOQDs) can be used in different applications such as optoelectronic and biomedical applications, respectively. Hence, the selective synthesis of GQDs and GOQDs is highly desirable but challenging. Here, we present GQDs and GOQDs selectively prepared by an easy and simple pulsed laser ablation in liquid (PLAL) method by controlling the laser wavelength. The obtained GQDs and GOQDs showed a significantly different optoelectronic nature mainly due to the existence of surface oxygen-rich functional groups (e.g. carboxyl or hydroxy groups). Also, we described a possible mechanism for the formation of oxygen functional groups during the PLAL process based on the Coulomb explosion model, which can give further insight for designing functional carbon materials.
- Published
- 2019
20. Graphene Oxide Quantum Dots Derived from Coal for Bioimaging: Facile and Green Approach
- Author
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Yong Son, Sungwook Mhin, Kang Min Kim, Taeseup Song, Jeong Ho Ryu, HyukSu Han, Kyung-Hwan Jung, Kwang Bo Shim, Byoung-Soo Lee, and Suk Hyun Kang
- Subjects
0301 basic medicine ,Materials science ,Oxide ,lcsh:Medicine ,chemistry.chemical_element ,Nanotechnology ,Carbon nanotube ,Article ,law.invention ,Pulsed laser ablation ,03 medical and health sciences ,chemistry.chemical_compound ,0302 clinical medicine ,law ,Coal ,lcsh:Science ,Multidisciplinary ,business.industry ,Graphene ,lcsh:R ,Publisher Correction ,030104 developmental biology ,chemistry ,Quantum dot ,lcsh:Q ,business ,Carbon ,030217 neurology & neurosurgery - Abstract
Graphene oxide quantum dots (GOQDs) are usually prepared using expensive carbon precursors such as carbon nanotubes (CNT) or graphene under the strong acidic condition, which requires an additional purifying process. Here, we first develop a facile pulsed laser ablation in liquid (PLAL) technique for preparing GOQDs using earth-abundant and low-cost coal as a precursor. Only ethanol and coal are used to produce GOQDs with excellent optical properties. The prepared GOQDs exhibit excellent optoelectronic properties which can be successfully utilized in bioimaging applications.
- Published
- 2019
21. Stress-Induced α″ Martensitic Transformation Mechanism in Deformation Twinning of Metastable β-Type Ti-27Nb-0.5Ge Alloy under Tension
- Author
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Kyung Hoon Kim, Yong-Deok Im, Hyung-Giun Kim, Byoung-Soo Lee, Won Yong Kim, and Sung-Hwan Lim
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010302 applied physics ,Materials science ,Mechanical Engineering ,Alloy ,Metallurgy ,Stress induced ,Thermodynamics ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Mechanics of Materials ,Tension (geology) ,Metastability ,Diffusionless transformation ,0103 physical sciences ,engineering ,General Materials Science ,Deformation (engineering) ,0210 nano-technology ,Crystal twinning - Published
- 2016
22. Refining effect of electron beam melting on additive manufacturing of pure titanium products
- Author
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Hyung Giun Kim, Kyung Hwan Jung, Chang-Woo Lee, Byoung Soo Lee, Yong Keun Ahn, and Hyung-Ki Park
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Imagination ,Materials science ,Chemical substance ,media_common.quotation_subject ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,law.invention ,Magazine ,law ,General Materials Science ,media_common ,Refining (metallurgy) ,Mechanical Engineering ,Metallurgy ,Final product ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,chemistry ,Mechanics of Materials ,Cathode ray ,0210 nano-technology ,Science, technology and society ,Titanium - Abstract
The refining effect of electron beam melting (EBM) during the additive manufacturing of Ti products was studied by comparing unused Grade-2 commercially pure (CP) Ti powder to an equivalent powder that had been recycled 50 times. The pre-heating and blasting processes that occur during recycling were found to degrade the perfectly spherical morphology of the powder, and the concentration of O and N were also increased by about 15%. This resulted in it changing to a Grade-3 CP Ti powder; however, the purity of the final product was improved to Grade-1 CP Ti by the slight refining effect of the EBM process.
- Published
- 2017
23. Enhanced osseointegration of Ti6Al4V ELI screws built-up by electron beam additive manufacturing: An experimental study in rabbits
- Author
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Hyung Giun Kim, Byoung-Soo Lee, Kang-Sik Lee, Chang-Woo Lee, Hae-Jin Lee, and Gun-Hee Kim
- Subjects
musculoskeletal diseases ,Materials science ,Electron-beam additive manufacturing ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,Bone tissue ,01 natural sciences ,Osseointegration ,medicine ,Surface roughness ,Surface structure ,Composite material ,Titanium alloy ,Surfaces and Interfaces ,General Chemistry ,equipment and supplies ,musculoskeletal system ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,Surfaces, Coatings and Films ,Smooth surface ,Bone ingrowth ,surgical procedures, operative ,medicine.anatomical_structure ,0210 nano-technology - Abstract
In the present study, the osseointegration of additively manufactured screws with a micro-rough surface structure and conventionally machined Ti6Al4V ELI screws with a smooth surface structure is compared. Screws were implanted in rabbit femurs or tibiae for two weeks. The additively manufactured screws exhibited a micro-rough surface with attached semi-molten powder with a size of 50–100 μm and blunt threads, whereas the conventionally machined screws showed a smooth surface and sharp threads. The bonding strength of the additively manufactured screws was significantly higher than that of the conventionally machined screws. The additively manufactured screws showed higher bone-to-implant contact than the conventionally machined screws. Considerable amount of bone tissue on the surface of the additively manufactured screws remained after the push-out tests, and the rabbit tibiae with the additively manufactured screws were significantly damaged, indicating a higher osseointegration rate. Active osteogenesis was observed around the semi-molten powder of the additively manufactured screws, and new bone was well developed along the micro-rough surface. Overall, this study shows that the micro-rough surface improved the bone ingrowth and suggests that additively manufactured screws may be an alternative to conventionally machined screws.
- Published
- 2020
24. Pulsed laser ablation based synthetic route for nitrogen-doped graphene quantum dots using graphite flakes
- Author
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Suk Hyun Kang, Yong Son, Byoung-Soo Lee, Young Kyu Jeong, Kyung Hwan Jung, Jeong Ho Ryu, Kang Min Kim, and Won Rae Kim
- Subjects
Photoluminescence ,Materials science ,General Physics and Astronomy ,chemistry.chemical_element ,Quantum yield ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,law.invention ,law ,Graphite ,Spectroscopy ,business.industry ,Graphene ,Surfaces and Interfaces ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Graphene quantum dot ,0104 chemical sciences ,Surfaces, Coatings and Films ,chemistry ,Quantum dot ,Optoelectronics ,0210 nano-technology ,business ,Carbon - Abstract
Graphene quantum dots (GQDs) prepared by pulsed laser ablation in liquid (PLAL) process face barriers to commercialization due to their poor optical properties and the use of expensive carbon precursors. In this work, we report a one-step route for the preparation of N-doped graphene quantum dots (NGQDs) with excellent optical properties using a low-cost carbon precursor. The as-prepared NGQDs exhibited excellent optical properties and high quantum yield compared to pristine graphene quantum dots (0.8% → 9.1%) due to the presence of the N atoms. A possible recombination mechanism of NGQDs was investigated by time-resolved photoluminescence spectroscopy. The increase of N atoms incorporated in the GQDs resulted in an increased fraction of the short recombination lifetime from the intrinsic state. We also report a possible mechanism for the formation of the N atoms in the GQDs structure during the PLAL process, which is explained based on the plasma plume, cavitation collapse, and nitrogen precursor decomposition model.
- Published
- 2020
25. Unidirectional columnar microstructure and its effect on the enhanced creep resistance of selective electron beam melted Inconel 718
- Author
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Hyun-Uk Hong, Hae-Jin Lee, Byoung-Soo Lee, Sun-Young Jun, So-Young Im, Jiwon Lee, and Je-Hyun Lee
- Subjects
Materials science ,Mechanical Engineering ,Metals and Alloys ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,0104 chemical sciences ,Superalloy ,Creep ,Mechanics of Materials ,Materials Chemistry ,Grain boundary ,Texture (crystalline) ,Composite material ,0210 nano-technology ,Inconel ,Burgers vector ,Electron backscatter diffraction - Abstract
In this study, the selective electron beam melting (SEBM) process was used to fabricate Inconel 718 superalloy, and their microstructures and creep resistances were investigated. The proper SEBM condition ensuring a relative density higher than 99.9% was found in electron beam current range of 24–30 mA at a scanning speed of 4500 mm/s and a preheat temperature of 1025 °C, from which the SEBMed Inconel 718 exhibited an unidirectional columnar grain microstructure with a strong texture along building direction. It was suggested that the local thermal condition during solidification after SEBM facilitates a continuation of epitaxial growth of crystals on layer beneath. The γ″ precipitates formed in the as-built condition regardless of focus offset, and their size increased with increasing focus offset from 1 to 12 mA. The creep rupture life of the as-built sample fabricated with focus offset of 12 mA showed 2 times longer than that of conventional forged Inconel 718 subjected to full heat treatment under creep condition of 650 °C/700 MPa. EBSD analysis on the crept samples indicated that strain accumulation was significant at the porosities and the high-angle grain boundaries. Additionally, the grain boundaries inclined to loading axis were more damaged during creep. The γ″ particles were occasionally sheared by matrix dislocations with Burger vector of a/2 , without leaving stacking faults behind. The enhanced creep resistance of SEBMed Inconel 718 superalloy can be attributed to the columnar microstructure with a strong texture and the high density of dislocations resulted from strong interaction with the γ″ particles.
- Published
- 2020
26. Role of strain-induced martensitic transformation on extrusion and intrusion formation during fatigue deformation of biomedical Co–Cr–Mo–N alloys
- Author
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Kenta Yamanaka, Akihiko Chiba, Takuya Mitsunobu, Hiroaki Matsumoto, Yunping Li, Byoung Soo Lee, and Yuichiro Koizumi
- Subjects
Materials science ,Polymers and Plastics ,Metallurgy ,Alloy ,Metals and Alloys ,engineering.material ,Electronic, Optical and Magnetic Materials ,Phase (matter) ,Diffusionless transformation ,Ceramics and Composites ,engineering ,Partial dislocations ,Extrusion ,Composite material ,Deformation (engineering) ,Dislocation ,Burgers vector - Abstract
The mechanism of extrusion and intrusion formation in Co–Cr–Mo–N alloys during fatigue deformation was investigated. In particular, we focused on the role of the strain-induced martensitic transformation (SIMT), which is the transformation of the metastable γ face-centered cubic (fcc) phase into a stable e hexagonal close-packed (hcp) phase at room temperature because of the gliding of Shockley partial dislocations in the γ-phase matrix. We found that the SIMT also plays a crucial role in the formation of extrusions and intrusions. Further, the morphology of the extrusions and intrusions formed in the Co–Cr–Mo–N alloy specimens was very different from that seen in other fcc alloys. The extrusions and intrusions were formed by the gliding of perfect dislocations with a Burgers vector of perfect dislocation on the basal plane of the e-hcp phase. This suggests that the e-phases introduced by the SIMT can deform readily.
- Published
- 2014
27. Collective behavior of strain-induced martensitic transformation (SIMT) in biomedical Co–Cr–Mo–N alloy polycrystal: An ex-situ electron backscattering diffraction study
- Author
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Akihiko Chiba, Hiroaki Matsumoto, Byoung Soo Lee, and Yuichiro Koizumi
- Subjects
Materials science ,Condensed matter physics ,Mechanical Engineering ,Condensed Matter Physics ,Crystallographic defect ,Crystallography ,Electron diffraction ,Mechanics of Materials ,Stacking-fault energy ,Diffusionless transformation ,Partial dislocations ,General Materials Science ,Texture (crystalline) ,Deformation (engineering) ,Electron backscatter diffraction - Abstract
Collective behavior of strain induced martensitic transformation (SIMT) in biomedical Co–Cr–Mo–N alloy polycrystal has been investigated by ex-situ electron backscattering diffraction (EBSD) analysis during tensile deformation. The formation of SIMTed e-hcp phase depends on the crystal orientation, and the SIMT behavior is basically understood by the motion of isolated Shockley partial dislocation associated with the negative stacking fault energy (SFE) of this alloy. However, their variant selection is not governed by Schmid׳s law. Most of SIMT occurred in grains with loading axes near and between 〈1 1 1〉 and 〈0 1 1〉 directions because of the low effective SFE, which is determined by the difference in the Schmid factors for leading and trailing Shockley partial dislocations. In grains with loading axes near the 〈0 0 1〉 direction, the SIMT did not occur due to the high value of the effective SFE. These findings are very important to improve the strength and wear resistance of this alloy without sacrificing the ductility by controlling the crystal texture.
- Published
- 2014
28. Asymmetric slip trace formation in tension/compression cyclic deformation of biomedical Co–Cr–Mo–N alloy with negative stacking fault energy
- Author
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Byoung Soo Lee, Yuichiro Koizumi, Akihiko Chiba, and Takuya Mitsunobu
- Subjects
Diffraction ,Materials science ,Mechanical Engineering ,Alloy ,Metals and Alloys ,Slip (materials science) ,Electron ,engineering.material ,Condensed Matter Physics ,law.invention ,Condensed Matter::Materials Science ,Crystallography ,Optical microscope ,Mechanics of Materials ,law ,Stacking-fault energy ,Metastability ,engineering ,Partial dislocations ,General Materials Science ,Composite material - Abstract
Surface relief formation of a biomedical Co–Cr–Mo–N (CCMN) alloy under tension/compression cyclic deformation has been investigated by in situ optical microscopy, atomic force microscopy and electron backscattering diffraction analysis. The formation of slip traces exhibited tension/compression asymmetry, resulting in unique surface reliefs. This is attributed to the motion of isolated Shockley partial dislocations in the metastable γ-face-centered cubic phase, in which the stacking fault energy is negative.
- Published
- 2014
29. Strain-induced martensitic transformation near twin boundaries in a biomedical Co–Cr–Mo alloy with negative stacking fault energy
- Author
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Yunping Li, Akihiko Chiba, Kazuhisa Sato, Shingo Kurosu, Yuichiro Koizumi, Sho Suzuki, Kenta Yamanaka, Hiroaki Matsumoto, and Byoung Soo Lee
- Subjects
Materials science ,Polymers and Plastics ,Metallurgy ,Metals and Alloys ,Slip (materials science) ,Electronic, Optical and Magnetic Materials ,Electron diffraction ,Residual stress ,Stacking-fault energy ,Diffusionless transformation ,Ceramics and Composites ,Composite material ,Deformation (engineering) ,Crystal twinning ,Electron backscatter diffraction - Abstract
Biomedical Co–Cr–Mo (CCM) alloys have been commonly used for artificial hip and knee joint prostheses, but a need to improve their biomedical inertness and wear resistance has become widely recognized. The mechanical behavior of CCM alloys is dominated by strain-induced martensitic transformation (SIMT), which causes crack initiation during plastic deformation but dramatically enhances the wear resistance in practical use. To develop more reliable CCM alloys it is essential to clarify the factors affecting the occurrence of SIMT. In the present study we have focused on the effect of annealing twin boundaries (ATBs) on SIMT behavior. We have analyzed in detail the substructures near a parallel pair of ATBs after deformation under a stress preferential for slip parallel to the ATBs. Preferential formation of e-hexagonal close-packed (HCP) phase at ATBs in metastable γ-face-centered cubic (FCC) phase was found by both scanning electron microscopy with electron backscattered diffraction (EBSD) analysis and transmission electron microscopy (TEM). High resolution TEM images indicated that thickening of the e-HCP phase does not proceed regularly on every second atomic plane, which would form perfect e-phase HCP structure, but irregularly leaving a high density of stacking faults. Furthermore, the thickness of the e-HCP phase was found to be different at ATBs on the two sides of the twin. The difference was attributed to the internal stress due to strain incompatibility at the ATBs on the basis of residual stress analysis by the EBSD–Wilkinson method and phase-field simulation of solute segregation at ATBs.
- Published
- 2013
30. The Influence of Aging Treatment on the Mechanical and Electrical Properties of Cu-Be Alloy
- Author
-
Byoung-Soo Lee, Myung-Ho Kim, Min Ryou, and Bong-Yong Jeong
- Subjects
Engineering drawing ,Materials science ,Precipitation (chemistry) ,Alloy ,engineering.material ,Microstructure ,chemistry.chemical_compound ,Beryllide ,chemistry ,Electrical resistivity and conductivity ,Mechanical strength ,engineering ,Composite material ,Tem analysis - Abstract
The influence of aging treatment on the microstructure, mechanical and electrical properties of Cu-Be alloy for connector material applications was investigated. The properties of mechanical strength and electrical conductivity were found to increase with increasing aging temperature. By the way, SEM/EDS and TEM analysis exhibited that beryllides precipitation (CoBe and NiBe) with a size of 50 nm were distributed in grains. It was, therefore concluded that these beryllide precipitates improved the mechanical strength and also it was favor in increasing of electrical conductivity.
- Published
- 2011
31. Deformation mode in biomedical Co–27% Cr–5% Mo alloy consisting of a single hexagonal close-packed structure
- Author
-
Hiroaki Matsumoto, Shingo Kurosu, Yunping Li, Byoung Soo Lee, and Akihiko Chiba
- Subjects
musculoskeletal diseases ,Diffraction ,Materials science ,Condensed matter physics ,Mechanical Engineering ,Alloy ,technology, industry, and agriculture ,Metals and Alloys ,Close-packing of equal spheres ,Slip (materials science) ,Electron ,engineering.material ,Condensed Matter Physics ,body regions ,Physics::Fluid Dynamics ,Condensed Matter::Materials Science ,Crystallography ,Mechanics of Materials ,Critical resolved shear stress ,Ultimate tensile strength ,engineering ,General Materials Science ,Crystallite - Abstract
The deformation mode of polycrystalline Co–27Cr–5Mo (in mass%) alloy consisting of the hexagonal close-packed e phase was examined. Basal 〈a〉 and prismatic 〈a〉 slips were the dominant deformation modes. The activation of these 〈a〉 slips is strongly dependent on Schmid factor, which indicates that the values of critical resolved shear stress for basal 〈a〉 slip and prismatic 〈a〉 slip are similar. For tensile strains up to 10%, the frequent occurrence of deformation twins could not be confirmed by electron backscattered diffraction analysis.
- Published
- 2010
32. DEVELOPMENT OF HIGH STRENGTH AND HIGH CONDUCTIVITY <font>Cu–Ag</font> ALLOY FOR MEDICAL ULTRASOUND EQUIPMENT
- Author
-
Hyung-Ho Jo, Byoung-Soo Lee, and Hoon Cho
- Subjects
Materials science ,High conductivity ,business.industry ,Metallurgy ,Surfaces and Interfaces ,Condensed Matter Physics ,Homogenization (chemistry) ,Surfaces, Coatings and Films ,Electrical resistivity and conductivity ,Ultimate tensile strength ,Materials Chemistry ,business ,Dissolution ,Medical ultrasound ,Thermal energy ,Solid solution - Abstract
The effect of thermal heat treatment on the mechanical and electrical properties of Cu–Ag alloys was investigated. The homogenization heat treatment leads to an increase in tensile strength and a decrease in electrical conductivity due to dissolution of Ag into copper matrix. Also, it is shown that electrical conductivity of as-cast Cu–Ag alloys decreases with increasing Ag content. In contrast, the aging heat treatment gives rise to increase both the tensile strength and electrical conductivity because the Ag solute diffuses out from copper matrix during aging heat treatment. Therefore, it can be mentioned that the electrical conductivity of Cu–Ag alloys depends on Ag solute in copper matrix. Also, aging treatment is favorable to acquire high strength and high electrical conductivity.
- Published
- 2010
33. DEVELOPMENT OF HIGH STRENGTH AND HIGH CONDUCTIVITY Cu–Ag ALLOY FOR MEDICAL ULTRASOUND EQUIPMENT
- Author
-
HOON CHO, BYOUNG-SOO LEE, and HYUNG-HO JO
- Subjects
High strength and high conductivity, micro-multicable, ultrasonic diagnostic, solid solution, aging - Abstract
The effect of thermal heat treatment on the mechanical and electrical properties of Cu–Ag alloys was investigated. The homogenization heat treatment leads to an increase in tensile strength and a decrease in electrical conductivity due to dissolution of Ag into copper matrix. Also, it is shown that electrical conductivity of as-cast Cu–Ag alloys decreases with increasing Ag content. In contrast, the aging heat treatment gives rise to increase both the tensile strength and electrical conductivity because the Ag solute diffuses out from copper matrix during aging heat treatment. Therefore, it can be mentioned that the electrical conductivity of Cu–Ag alloys depends on Ag solute in copper matrix. Also, aging treatment is favorable to acquire high strength and high electrical conductivity.
- Published
- 2010
34. Estimation of Energy Requirements and Atmospheric Emission in Continuous Casting Process for Al Wire
- Author
-
Hyung Ho Jo, Byoung Soo Lee, and Hoon Cho
- Subjects
Materials science ,Annealing (metallurgy) ,Manufacturing process ,Mechanical Engineering ,Metallurgy ,chemistry.chemical_element ,Condensed Matter Physics ,Energy requirement ,Continuous casting ,chemistry ,Mechanics of Materials ,Aluminium ,General Materials Science ,Extrusion ,Atmospheric emissions - Abstract
Energy requirement and yield for production of aluminum wirerods manufactured by continuous casting process were investigated to enhance yield of aluminum wiredrods. Also, it was compared with conventional process including extrusion process. The enhancement of yield more than 30% could be accomplished through the continuous casting process. The conventional process including extrusion process for production of wirerods consumes more energy compared to continuous casting. In addition, a number of intermediate annealing may be introduced during wiredrawing process of wirerods manufactured by conventional process including extrusion process. It can be mentioned that continuous casting process is suitable process for wiredrawing process because it can save energy requirement not only during manufacturing process of wirerods but also during following wiredrawing process.
- Published
- 2009
35. Eco-Friendly Grain Refinement for A3003 Alloy
- Author
-
Jae Hong Ha, Byoung Soo Lee, Je Sik Shin, Hoon Cho, and Sung Ho Chang
- Subjects
6111 aluminium alloy ,Materials science ,Mechanical Engineering ,Metallurgy ,Alloy ,Nucleation ,chemistry.chemical_element ,engineering.material ,Condensed Matter Physics ,Grain size ,Grain growth ,chemistry ,Mechanics of Materials ,Aluminium ,Phase (matter) ,engineering ,General Materials Science ,Carbon - Abstract
Eco-friendly grain refinement of A3003 alloy was studied by addition of non-toxic Al-Ti alloy because of toxic-fluorine in Al-Ti-B alloys which used as a representative grain refiner for aluminum and its alloys. TiAl3 phase in Al-Ti alloy bring to decrease grain size of A3003 alloy. But, grain growth occurred with prolonged holding time due to the solution of Ti into aluminum matrix. In contrast, lasting grain refinement of A3003 alloy was occurred in graphite crucible. It can be mentioned that carbon comes from graphite crucible was combined with Ti solute in aluminum melt and then TiC acts as a heterogeneous nucleation for A3003 alloy.
- Published
- 2009
36. Anisotropy Control of Cold Rolled Cu-Ag Alloys
- Author
-
Hoon Cho, Byoung Soo Lee, Jae Hong Ha, and Hyung Ho Jo
- Subjects
Materials science ,Annealing (metallurgy) ,Electrical resistivity and conductivity ,Metallurgy ,Mechanical strength ,Alloy ,Ultimate tensile strength ,General Engineering ,engineering ,Conductivity ,engineering.material ,Anisotropy ,Eutectic system - Abstract
The anisotropy in mechanical strength and electrical conductivity in Cu-Ag alloy during cold rolling were investigated. The anisotropy in tensile strength and electrical conductivity was significant with increasing Ag content in Cu-Ag alloy. The cold rolled Cu-Ag alloys with higher Ag content have filamentary structure, which is composed of elongated eutectic phase and Cu matrix. In addition, the eutectic phase in Cu-Ag alloys with higher Ag content has a strong α-fiber texture. It can be mentioned that the eutectic phase in filamentary structure is promotes the anisotropy of electrical conductivity of Cu-Ag alloys. This strong a-fiber texture of eutectic phase was decreased by annealing process (300 OC for 1h), and the anisotropy in strength and conductivity was decreased.
- Published
- 2008
37. Ageing Behavior of Cu-Ag Alloys
- Author
-
Byoung Soo Lee, Bok Hyun Kang, Ki-Young Kim, and Hoon Cho
- Subjects
International Annealed Copper Standard ,Solid solution strengthening ,Materials science ,Fabrication ,Electrical resistivity and conductivity ,Ultimate tensile strength ,Metallurgy ,Alloy ,General Engineering ,Hardening (metallurgy) ,engineering ,engineering.material ,Solid solution - Abstract
To develop Cu alloy with tensile strength of 800 MPa and electrical conductivity of 80 %IACS (International Annealed Copper Standard), the variation of mechanical strength and electrical conductivity in Cu-Ag alloy during fabrication processes including casting, solid solution and ageing treatment were investigated. Solid solution hardening leads to a large drop in electrical conductivity of Cu-Ag alloys due to super-saturation of Ag solute in Cu matrix. Ageing hardening gives rise to enhance both of the mechanical strength and the electrical conductivity. Therefore, it can be mentioned that the electrical conductivity of Cu-Ag alloys was affected dominantly by Ag solute in Cu matrix.
- Published
- 2008
38. Modeling of a Transmission Control Cable for Vibration Analysis
- Author
-
Hae-Woon Choi and Byoung-Soo Lee
- Subjects
Lever ,Engineering ,business.product_category ,Torsional vibration ,Noise measurement ,Noise (signal processing) ,business.industry ,Acoustics ,Vibration ,Harmonic analysis ,Transmission (telecommunications) ,Active vibration control ,Electronic engineering ,business - Abstract
A transmission control cable connects the transmission control arm and the control lever mechanically and transfers control effort exerted by a driver to the transmission. It also transfers vibration generated by the engine to the passenger room through mechanical connection. To understand vibration and noise transfer mechanism and to further find a way to suppress the transmission of vibration effectively, a dependable dynamic vibration model is a necessity. A vibration model for a transmission control cable is developed and a simulation study has been conducted to obtain mode frequencies and a transmittability. The resonance frequencies obtained by an harmonic analysis is compared with the noise level measurement data. The measurement agrees with the simulation result thus ensures the reliability of the model.
- Published
- 2008
39. Automotive Windshield Wiper Linkage Dynamic Modeling for Vibration Analysis
- Author
-
Byoung-Soo Lee
- Subjects
Engineering ,Computer simulation ,business.industry ,Mechanical engineering ,Stiffness ,Linkage (mechanical) ,Multibody system ,Automotive engineering ,law.invention ,Vibration ,law ,Bushing ,Windshield ,medicine ,medicine.symptom ,business ,Actuator - Abstract
An automotive windshield wiper system is modeled mainly for vibration analysis purpose. The model is composed of solid links, ideal joints, imperfect joints to simulate unavoidable manufacturing defects and bushings having stiffness, contact between a wiper blade and a wind screen glass, friction, a spring and an actuator. Main stream of wiper dynamics analysis has been obtaining a closed form of system of equations using Newton`s or Lagrange`s formula and doing a numerical simulation study to understand and predict the behavior of it. However, the modeling process is complex since a wiper system is of multibody and a contact problem occurs. When imperfection, such as dead zone of a joint and stiffness of a rubber bushing, should be included, the added complexity makes the modeling difficult. Since the imperfection is understood as main cause of problematic vibration, the dynamics model of a wiper system aiming vibration analysis should include such unavoidable manufacturing defects in the model. An open form of dynamic model of a automotive windshield wiper system with imperfect joints using a commercial software is obtained and a simulation analyssis is conducted for vibration reduction study.
- Published
- 2008
40. Development of A3003 Alloy Tube for Eco-Friendly Refrigerant Application
- Author
-
Hoon Cho, Hyung Ho Jo, and Byoung Soo Lee
- Subjects
Materials science ,Mechanical Engineering ,Metallurgy ,Alloy ,engineering.material ,Condensed Matter Physics ,Microstructure ,Environmentally friendly ,Refrigerant ,Mechanics of Materials ,Particle-size distribution ,engineering ,General Materials Science ,Tube (fluid conveyance) ,Extrusion ,Ductility - Abstract
The influence of extrusion temperature and Ti content was investigated by observing the microstructure and determining the mechanical strength of A3003 alloy tube. The A3003 alloy was modified by inoculation in terms of addition of Ti and then extruded at the various extrusion temperatures. In case of A3003 alloy tube without addition of Ti, the yield strength was slightly improved with decreasing extrusion temperature. On the other hand, the yield strength was improved markedly in A3003 alloy tube with small addition of Ti, and also ductility was slightly reduced. Grain size distribution from observing the microstructure was different with addition of Ti. Coarse grains were formed on the outer and inner parts of the alloy tube without addition of Ti, whereas the finer grains were uniformly distributed in the alloy tube with addition of Ti. Thus the microstructure and mechanical strength of A3003 alloy tube could be controlled by addition of Ti. Threefore, optimum Ti content and extrusion temperature to fabricate high yield strength and ductility A3003 alloy tube (σy=60 MPa, ε=30%) for eco-friendly refrigerant application are above 0.05wt.Ti and below 480 °C, respectively. Introduction
- Published
- 2008
41. Influence of Annealing Atmosphere on the Mechanical and Wear Properties of Free-Cutting Phosphor Bronze Alloy
- Author
-
Byoung Soo Lee, Hyung Ho Jo, Hak Young Kim, and Hoon Cho
- Subjects
Phosphor bronze ,Materials science ,Annealing (metallurgy) ,Alloy ,Metallurgy ,General Engineering ,engineering.material ,Wear resistance ,Condensed Matter::Materials Science ,Vaporization ,Air atmosphere ,engineering ,Annealing atmosphere ,Softening ,Physics::Atmospheric and Oceanic Physics - Abstract
The influence of annealing atmosphere on mechanical and wear properties of free-cutting phosphor bronze alloy was investigated. After annealing in vacuum, the mechanical properties of the alloy decreases due to vaporization of alloying element. In addition, the softening of matrix induces decreasing the wear resistance dramatically. In contrast, high mechanical properties were observed in the alloy annealed in air and in nitrogen atmosphere. In particular, a large smearing of lead in the alloy annealed in air atmosphere was observed and was affected on the enhancement of wear resistance. Consequently, annealing in vacuum atmosphere is not suitable for high mechanical properties and wear resistance.
- Published
- 2007
42. Influence of ECAP Routes on the Microstructure and Mechanical Properties of Hot Extruded 3003 Al Alloy
- Author
-
Hoon Cho and Byoung Soo Lee
- Subjects
Equiaxed crystals ,Materials science ,Alloy ,Metallurgy ,engineering.material ,Deformation (meteorology) ,Condensed Matter Physics ,Microstructure ,Atomic and Molecular Physics, and Optics ,Grain size ,engineering ,General Materials Science ,Extrusion ,One pass - Abstract
The microstructures and mechanical properties of unidirectional deformation structured Al alloy during ECAP with various deformation routes were investigated. In order to fabricate unidirectional deformation structure for Al alloy, hot extrusion was carried out. It was found that the deformation route A in ECAP routes is the dominant route for the grain refinement and strengthening. In deformation route A, the high strength ultra-fine grained Al alloy with a grain size of ~ 200 nm was obtained due to the accumulation of consecutive strain process. In contrast, the strength of ECAP’ed Al alloy produced via deformation route C was greatly increased after one pass because the grains were strained and cancelled each pass. By contrast, the equiaxed grains were obtained in deformation route BC because the sample was rotated 90 O in the same sense in each pass. The deformation route BC was superior to the deformation route C because the deformation route BC was more favorable than the deformation route C in the accumulation of consecutive strain. It is also found that unidirectional deformation structured Al alloy via hot extrusion shows similar grain refinement tendency with equiaxed structured Al alloy during ECAP processing.
- Published
- 2007
43. Fabrication of micro condenser tube through direct extrusion
- Author
-
Duck-Young Hwang, Hoon Cho, Hyung-Ho Jo, and Byoung-Soo Lee
- Subjects
Materials science ,Metallurgy ,Alloy ,Metals and Alloys ,Refrigeration ,engineering.material ,Industrial and Manufacturing Engineering ,Computer Science Applications ,Refrigerant ,Modeling and Simulation ,Heat exchanger ,Ceramics and Composites ,engineering ,Brazing ,Tube (fluid conveyance) ,Extrusion ,Condenser (heat transfer) - Abstract
In accordance with environmental regulations on refrigeration technology, the commercial A1100 alloy condenser tube that has widely been used in CFC and HCFC refrigerant systems and operated at a low working pressure (10–30 bar) was inappropriate to the eco-friendly CO 2 refrigerant systems which possess a high working pressure (60–80 bar) due to the low mechanical properties. As a result, the stiffness of the conventional 1000 series alloys might not be appropriate in this requirement. The present study is mainly aimed at developing condenser tube material such as A3003 alloy for the application of eco-friendly refrigerants with higher working pressure rather than for conventional CFC and HCFC refrigerants. The mechanical properties and pressurized strength of condenser tube are greatly affected by the coarse grains, which grow during the brazing process. According to the pressurized testing, A3003 alloy is more suitable than A1100 alloy when the condenser tube is applied to eco-friendly refrigerants usage because A3003 alloy can be durable in a heat exchanger which requires high working pressure.
- Published
- 2007
44. Effect of Annealing on the Mechanical Property and Machinability of Free-Cutting Phosphor Bronze Alloy
- Author
-
Hyung Ho Jo, Byoung Soo Lee, Jin Seok Yang, and Hoon Cho
- Subjects
Phosphor bronze ,Materials science ,Annealing (metallurgy) ,Mechanical Engineering ,Machinability ,Alloy ,Metallurgy ,Recrystallization (metallurgy) ,engineering.material ,Condensed Matter Physics ,Continuous casting ,Grain growth ,Mechanics of Materials ,Ultimate tensile strength ,engineering ,General Materials Science ,Composite material - Abstract
Free-cutting phosphor bronze alloy (ASTM C54400) was used as a material for automotive parts and industrial valve parts for its high strength, machinability and excellent corrosion resistance. To obtain desired mechanical strength of the alloy, the process parameters including continuous casting speed, reduction in area and annealing temperature have to be controlled. In this study, we investigated the effect of annealing on the mechanical property and machinability of free-cutting phosphor bronze alloy fabricated by continuous casting with different casting speeds of 80, 100, and 120 m/min, respectively. After annealing, the tensile strength of the alloy decreased with increasing annealing time owing to the occurrence of recrystallization and grain growth. In the cast and swaged alloy produced at casting speed of 120 m/min, the grain growth occurred rapidly. In contrast, in the alloy produced at the casting speed of 80 m/min, the grains growth rate was low. Furthermore, the effect of Pb particle in the alloy on machinability was also investigated by using a tool dynamometer installed force sensor.
- Published
- 2007
45. Modification of A3003 Alloy for Development of High Toughness Al Alloy Tube
- Author
-
Hoon Cho, Byoung Soo Lee, and Hyung Ho Jo
- Subjects
Toughness ,Materials science ,Mechanical Engineering ,Metallurgy ,Alloy ,engineering.material ,Condensed Matter Physics ,Grain size ,Dendrite (crystal) ,Mechanics of Materials ,engineering ,6063 aluminium alloy ,Formability ,General Materials Science ,Elongation ,Deformation (engineering) - Abstract
The strength of aluminum alloys was improved by a severe deformation process while the decrease of elongation leads to the defect. Modification of A3003 alloy was attempted in order to develop a high strength and high formability Al alloy tube for the application of air-conditioning systems in transportation, such as passenger planes and automobiles. An A3003 alloy was modified by Ti addition, grain refiner. As a result of modification, the modified A3003 alloy was able to suitably satisfy the mechanical strength requirements, including elongation. Grain size and secondary dendrite arm spacing of A3003 alloy decreased by as much as 50 % by Ti addition. The finer grains were uniformly distributed in the modified A3003 alloy billet. The yield strength of the modified A3003 alloy was improved by 30 % without decreasing elongation.
- Published
- 2007
46. Web Accessibility Evaluation of Cyber Universities' Contents in Korea
- Author
-
Ji-Sun Lee and Byoung-Soo Lee
- Subjects
World Wide Web ,Web standards ,Engineering ,Government ,Web Accessibility Initiative ,business.industry ,business ,Web accessibility - Abstract
This paper analyzes if the rapidly increasing cyber universities` remote education provides services based on web accessibility standard and suggest the direction to reduce information difference between people. It selected 10 cyber universities recognized by the government and analyzed the application situation of the web accessibility using` A-Prompt`, an evaluation and analysis tool for web accessibility focusing on factors that can be evaluated technically. It also compared it with cyber universities remote education web accessibility result performed in 2006 to confirm if the accessibility is improved according to `web contents accessibility instruction (KWCAG) 1.0. The result shows that the items such as the use of text and the support of supplementary explanation tool have improved. But it was analyzed that it is difficult for people to use web contents provided by domestic cyber universities. So the educational contents` accessibility application must be considered to solve such problems and publicize the remote education.
- Published
- 2007
47. Microstructures and Mechanical Properties of Melt Extruded Al-Cu Alloys
- Author
-
Byoung Soo Lee, Myung-Ho Kim, and Dae Heon Joo
- Subjects
Fabrication ,Materials science ,business.product_category ,Metallurgy ,Alloy ,chemistry.chemical_element ,engineering.material ,Condensed Matter Physics ,Microstructure ,Copper ,Casting ,Atomic and Molecular Physics, and Optics ,Grain size ,chemistry ,engineering ,Die (manufacturing) ,General Materials Science ,Extrusion ,business - Abstract
Melt extrusion is a new fabrication process with the characteristics of both casting and extrusion. In this process, a metallic melt which is poured and solidified up to semisolid state in the container can be directly extruded through the die exit to form a product of bar shape without other intermediate processes. The effects of various process parameters, such as melt temperature and extrusion ratio, on the extrusion behavior of Al-Cu alloys in the semisolid state were investigated. Mechanical properties of the melt extruded Al-Cu alloy were measured and its characteristics are compared with the microstructure and copper contents in the alloy. Al-Cu alloys were successfully extruded after squeezing out of liquid during the melt extrusion with smaller force (60 Mpa) compared to the solid extrusion. Al-Cu alloys bar with the mean grain size of 200 μm was fabricated by melt extrusion; however, the mechanical properties have nothing to do with the extrusion ratio. The squeezing out of liquid was get lead to the segregation of the alloys and was affect on the mechanical properties.
- Published
- 2006
48. Aging Behavior of Al-Cu Alloys Produced by Melt Extrusion Process
- Author
-
Byoung Soo Lee, Dae Heon Joo, Hyung Ho Jo, Hoon Cho, and Myung-Ho Kim
- Subjects
business.product_category ,Fabrication ,Materials science ,Bar (music) ,Alloy ,Metallurgy ,engineering.material ,Condensed Matter Physics ,Microstructure ,Casting ,Atomic and Molecular Physics, and Optics ,Grain size ,engineering ,Die (manufacturing) ,General Materials Science ,Extrusion ,business - Abstract
Melt extrusion is a new fabrication process with the characteristics of both casting and extrusion. In this process, a metallic melt which is poured and solidified up to semisolid state in the container can be directly extruded through the die exit to form a product of bar shape without other intermediate processes. The aging behavior of Al-Cu alloys in the semisolid state was investigated. And the microstructure and mechanical properties of the melt extruded Al-Cu alloy bar were measured and its characteristics are compared with those of a hot extruded Al-Cu alloy bar. Al-Cu alloys were successfully extruded after squeezing out of liquid during melt extrusion with smaller force compared to the solid extrusion. Al-Cu alloys bar with the mean grain size of up to 200 μm was fabricated by melt extrusion process. And the mechanical properties of the melt extruded Al-Cu alloy bar were improved after the T6 treatment.
- Published
- 2006
49. [Untitled]
- Author
-
Dong-Jun Kang, Sun-Geon Kim, and Byoung-Soo Lee
- Subjects
Nanocomposite ,Aqueous solution ,Materials science ,Silicon ,Mechanical Engineering ,Composite number ,Inorganic chemistry ,chemistry.chemical_element ,Nanoparticle ,Crystallinity ,Chemical engineering ,chemistry ,Mechanics of Materials ,General Materials Science ,Thermal stability ,Dispersion (chemistry) - Abstract
Various TiO2/SiO2 composite nanoparticles were prepared by vapor phase hydrolysis of Titanium Tetraisopropoxide (TTIP) and Tetraethylorthosilicate (TEOS) in a tubular reactor heated by electrical furnace by changing the methods of reactant mixing, the molar ratio of the precursors and the set temperature of the furnace. These variables affected the average size and the bulk composition of the particles as well as their morphological and crystalline structures. The morphological structures of the particles were reconfirmed as T-S, S-T and T/S as in the previous study. Various correlations were obtained between the molar ratio of the precursors, and the size, the composition and the TiO2 main peak intensity of the particles as a parameter of the mode of reactant mixing. In general, it was found that high content of silicon constituent showed translucent envelopes surrounding primary particles, which increased the dispersion diameter of the particles, reduced the thermal stability, retarded the anatase-to-rutile transformation and the initial photocatalytic degradation of phenol in an aqueous solution.
- Published
- 2003
50. Chaos maximizing optimal control
- Author
-
Byoung Soo Lee
- Subjects
Mechanical Engineering ,Synchronization of chaos ,Chaotic ,Lyapunov exponent ,Optimal control ,Nonlinear Sciences::Chaotic Dynamics ,symbols.namesake ,Mechanics of Materials ,Control theory ,Limit cycle ,Attractor ,symbols ,Applied mathematics ,Lyapunov equation ,Lyapunov redesign ,Mathematics - Abstract
A chaos maximizing optimal control problem is formulated and applied to Duffing's equation to maximize the largest Lyapunov exponent. The resulting bang-bang optimal controller yields a positive value of the largest Lyapunov exponent, indicating chaotic behavior. In fact, the largest Lyapunov exponent is approximately twice as large as that achieved with simple sinusoidal forcing at the same amplitude bounds. However, the resulting phase portrait of the optimal trajectory is a limit cycle and is not chaotic at all. This paradoxical result contradicts the basic theory that a bounded trajectory with at least one positive Lyapunov exponent must be chaotic. Details concerning the development of a chaos measurement that is viable for current optimal control theory, a method of continuous normalization, the paradoxical chaotic limit cycle, resolution of the paradox, and closed-loop optimal jump condition in an augmented space are presented. In particular, for systems of differential equations with only piecewise differentiable right-hand sides due to a switching control, a jump discontinuity condition must be imposed on the state perturbations in order to compute correct Lyapunov exponents.
- Published
- 1995
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