• Transactions of Materials Processing
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• v.11 no.7
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• pp.561-568
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• 2002

Micro tensile test is the most direct and convenient method to measure material properties such as Young's modulus and fracture strength. It, however, needs more accurate measurement system, mote stable and repetitive alignment and more sensitive gripping than conventional tensile test. Many researchers have put their effort on overcoming these difficulties for tile development of micro tensile tester, fabricating micro specimens of functional materials and measuring their properties. This paper will review the related vigorous researches over the world in the recent decade and explain how to apply them to a design of the fester which is under our own development.

• Korean Journal of Optics and Photonics
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• v.23 no.3
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• pp.124-127
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• 2012

We designed and fabricated dichroic filters for high-power fiber lasers to protect the pumping laser diode from counterpropagating laser beams. The transmittance at laser diode wavelengths of 905 nm~925 nm was designed to be less than 0.1% and the transmittance at the fiber laser or Brillouin scattering wavelengths of 1020 nm ~ 1100 nm was designed to be more than 99.9%. Since oxide materials have good adhesion to the $SiO_2$ substrate, $SiO_2/Ta_2O_5$ were used as coating materials. The filter was fabricated according to our optimized design and its characteristics were compared with the theoretical design. As a result, the transmittance at laser diode wavelengths of 905 nm~925 nm was measured to be less than 0.1%, and the transmittance at the fiber laser or Brillouin scattering wavelengths of 1020 nm~1100 nm was measured to be more than 95.5%, which coincided well with the theoretical design considering processing errors. The filter was found to operate well over 1W of input laser power.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.6
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• pp.712-721
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• 2006

Statement of problem. Acrylic resin is most commonly used for denture bases. However, acrylic resin has week points of volumetric shrinkage during polymerization that reduces denture fit. The expandability of POSS (Polyhedral Oligomeric Silsesquioxane) containing polymer could be expected to reduce the polymerization shrinkage of denture bases and would increase the adaptability of the denture to the tissue. Purpose. The purpose of this study was to compare the dimensional stability in the conventional acrylic resin base, POSS-containing acrylic resin base, and metal bases. Materials and methods. Thirty six maxillary edentulous casts and dentures of different base were fabricated. Tooth movement and tissue contour change of denture after processing (resin curing, deflasking, decasting and finishing without polishing) and immersion in artificial saliva at $37^{\circ}C$ for 1 week and 4 weeks were measured using digital measuring microscope and threedimensional laser scanner. Results. The results were as follows: 1. The conventional resin group showed significant (p<0.01) dimensional change throughout the procedure (processing and immersion in artificial saliva). 2. After processing, the metal group and POSS resin group showed lower linear and 3-dimensional change than conventional resin group (p<0.01). 3. There was no statistically significant linear and 3-dimensional change after immersion for 1 week and 4 weeks in metal and POSS resin group. 4. In all groups, the midline and alveolar ridge crest area presented smaller 3-dimensional change compared with vestibule and posterior palatal seal area after processing and soaking in artificial saliva for 1 week and 4 weeks (p<0.01). Conclusion. In this study, a reinforced acrylic-based resin with POSS showed good dimensional stability.

• Design & Manufacturing
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• v.17 no.3
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• pp.48-54
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• 2023

In this study, an injection mold with ultra-small surface properties was manufactured using nanosecond laser processing. A superhydrophobic characteristic analysis was performed on the PET specimen manufactured through this. To this end, a hydrophobic pattern was defined using the Cassie-Baxter model. The defined features were selected with a spot diameter of 25um and pitch spacing of 30um and 35um. As a result of the basic experiment, it was confirmed that the fine pattern shape had an aspect ratio of 1:1 when the pitch interval was 35um and 20 iterations. Through the determined processing conditions, a hydrophobic pattern was implemented on the core surface of KP4. A specimen with a hydrophobic pattern was produced through injection molding. The height of the molded hydrophobic pattern is 20 ㎛ less than the depth of the core and the contact angle measurement results are 92.1°. This is a contact angle smaller than the superhydrophobic criterion. Molding analysis was performed to analyze the cause of this, and it was analyzed that the molding was not molded due to the lack of pressure in the injection machine.

• Laser Solutions
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• v.10 no.3
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• pp.25-32
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• 2007

The effect of welding speed on the weldability, microstructures, hardness, tensile property of Nd:YAG laser welding joint in 600MPa grade precipitation hardening high strength steel was investigated. A shielding gas was not used, and bead-on-plate welding was performed using various welding speeds at a power of 3.5kW. Porosity in the joints occurred at 1.8m/min, but were not observed over the welding speed of 2.1m/min. However, spatter occurred over the welding speed of 6.6m/min. The hardness was the highest at heat affected zone(HAZ) near fusion zone(FZ), and was decreased on approaching to the base metal. The maximum hardness increased with increasing welding speed. The microstructure of FZ was composed of coarse grain boundary ferrite and bainite(upper) but the HAZ near the FZ contained bainite(Lower) and fine ferrite at a low welding speed. With increasing welding speed, ferrite at the FZ and the HAZ became finely and upper binite changed to lower bainite. In a perpendicular tensile test to the weld line, all specimens were fractured at the base metal, and the tensile strength and the yield strength of joints was equal to those of raw material. Elongation was found to be lower than that of the raw material.

• Transactions on Electrical and Electronic Materials
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• v.11 no.1
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• pp.1-10
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• 2010

This is an overview paper reporting our most recent work on processing and microstructure of nano-structured oxides and their photoluminescence and photo-catalysis properties. Zinc oxide and related transition metal oxides such as vanadium pentoxide and titanium dioxide were produced by a combination of magnetron sputtering, hydrothermal growth and atmosphere controlled heat treatment. Special morphology and microstructure were created including nanorods arrays, core-brushes, nano-lollipops and multilayers with very large surface area. These structures showed special properties such as much enhanced photoluminescence and chemical reactivity. The photo-catalytic properties have also been promoted significantly. It is believed that two factors contributed to the high reactivity: the large surface area and the interaction between different oxides. The transition metal oxides with different band gaps have much enhanced photoluminescence under laser stimulation. Use of these complex oxide structures as electrodes can also improve the energy conversion efficiency of solar cells. The mixed oxide complex may provide a promising way to high-efficiency photo emitting materials and photo-catalysts.

• Transactions of Materials Processing
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• v.32 no.4
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• pp.221-227
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• 2023

While tube bending is a conventional forming technique, it is still used to make curved products for load-bearing members or aesthetically pleasing parts in various manufacturing industries such as automotive, aerospace, and others. Whole or local deformation of the final product such as springback, distortion, or local buckling are of interest in metal forming or precision manufacturing. In this paper, the factors affecting the cross-sectional deformation are explored. A 5-axis stretch bending machine was used for two-dimensional bending with extruded AA6082-T4 rectangular tubes. Three different bending sequences were employed: stretch before bending, stretch after bending, simultaneous bending and stretch. Furthermore, by considering both the stretch and bending angle, cross-sectional deformation was also analyzed. It was observed that employing stretch bending techniques can effectively reduce cross-sectional deformation and contribute to overall quality enhancement. Through this study, it was revealed that these factors have an impact on the cross-sectional deformation of the tubes.

• Particle and aerosol research
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• v.6 no.3
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• pp.131-138
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• 2010

Flexible electronics are the electronics on flexible substrates such as a plastic, fabric or paper, so that they can be folded or attached on any curved surfaces. They are currently recognized as one of the most innovating future technologies especially in the area of portable electronics. The conventional vacuum deposition and photolithographic patterning methods are well developed for inorganic microelectronics. However, flexible polymer substrates are generally chemically incompatible with resists, etchants and developers and high temperature processes used in conventional integrated circuit processing. Additionally, conventional processes are time consuming, very expensive and not environmentally friendly. Therefore, there are strong needs for new materials and a novel processing scheme to realize flexible electronics. This paper introduces current research trends for flexible electronics based on (a) nanoparticles, and (b) novel processing schemes: nanomaterial based direct patterning methods to remove any conventional vacuum deposition and photolithography processes. Among the several unique nanomaterial characteristics, dramatic melting temperature depression (Tm, 3nm particle~$150^{\circ}C$) and strong light absorption can be exploited to reduce the processing temperature and to enhance the resolution. This opens a possibility of developing a cost effective, low temperature, high resolution and environmentally friendly approach in the high performance flexible electronics fabrication area.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.150-150
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• 2003

wide bind gap과 wurtzite hexagonal structure를 가지고 있으며 청색 발광 및 청자색 레이저 특성을 보이는 III-V족 화합물반도체 GaN는 laser diodes (LD) 및 light emitting diodes (LED) 재료로 주목받고있는 주요 전자재료이다. 본 연구에서는 GaN를 chemical vapor deposition (CVD) 법을 이용하여 vapor-liquid-solid (VLS) mechanisum에 의하여 GaN나노와이어 형태로 성장시켰다. 기판은 (001)Si을 사용하였고 suputtering을 이용하여 GaN와 AlN의 double buffer layer (DBL)를 증착시켰으며 촉매로는 Ni을 사용하였다. 또한, 원료로는 고순도 Ga금속과 NH$_3$ gas를, carrier gas로는 Ar을 사용하여 GaN/AlN/(001)Si 위에 GaN 나노와이어를 성장시켰다. 성장된 GaN 나노와이어는 DBL의 두께, Ga source의 양, 튜브 안의 압력, 튜브 안의 위치 등의 제 공정변수에 따라 tangled, straight 등의 다양한 형상을 보였으며 지름은 약 30~100 nm, 길이는 수 $\mu\textrm{m}$로 관찰되었다. GaN나노와이어의 결정성, 형상 및 발광특성 등을 x-ray diffraction (XRD), photoluminesence (PL), scanning electron microscope (SEM), transmision electron microscope (TEM) 등을 이용하여 측정하였으며 제 공정변수와의 상관관계를 규명하였다.

• Proceedings of the KAIS Fall Conference
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• 2004.06a
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• pp.267-269
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• 2004

본 연구에서는 일반적인 미세구조물 제작공정인 lithography 공정을 이용하지 않고 SLS(Selective Laser sintering)형 RP(Rapid Prototyping system)을 이용하여 패턴의 깊이가 400$\mu$m인 미세구조물을 제작하였다. 제작 공정변수 중 재료의 상태가 new powder 이고 배치각이 $0^{\circ}$ 일 때 패턴의 깊이, 선폭과 표면조도가 가장 잘 구현되었다.