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Search Results: 1 - 10 of 12379 matches for " Si-Young Kwak "
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Measurement of heat treatment induced residual stresses by using ESPI combined with hole-drilling method
Jie Cheng,Si-Young Kwak,Ho-Young Hwang
China Foundry , 2010,
Abstract: In this study, residual stresses in heat treated specimen were measured by using ESPI (Electronic Speckle-Pattern Interferometry) combined with the hole-drilling method. The specimen, made of SUS 304 austenitic stainless steel, was quenched and water cooled to room temperature. Numerical simulation using a hybrid FDM/FEM package was also carried out to simulate the heat treatment process. As a result, the thermal stress fields were obtained from both the experiment and the numerical simulation. By comparision of stress fields, results from the experimental method and numerical simulation well agreed to each other, therefore, it is proved that the presented experimental method is applicable and reliable for heat treatment induced residual stress measurement.
Impact analysis of casting parts considering shrinkage cavity defect
Si-Young Kwak,Jie Cheng,Jeong-Kil Choi
China Foundry , 2011,
Abstract: Shrinkage cavity may be detrimental to mechanical performances of casting parts. As a consequence, design engineers often use overly large safety factors in many designs due to insufficient understanding of quantitative effects of shrinkage cavity defects. In this paper, process of Al alloy wheel impact test was computationally analyzed for both the wheel models with and without shrinkage cavity defects. Based on shrinkage cavity data obtained from industrial CT (Computerized Tomography), the shrinkage cavity defects were modeled with SSM (Shape Simplification Method), which reconstructs shrinkage cavity defects to hollow spheroid primitives. After the impact simulation was conducted, the results show that under impact test condition, the wheel considering shrinkage cavity defects may fracture while the sound-assumed wheel may not.
Critical cooling rate on carbide precipitation during quenching of austenitic manganese steel
Youn-Soo Ham,Jeong-Tae Kim,Si-Young Kwak
China Foundry , 2010,
Abstract: Critical cooling rate to avoid carbide precipitation during quenching of austenitic manganese steel was investigated by means of optical microscopy, image analyzer and numerical analysis. An efficient heat treatment analysis program including temperature-dependent material properties was developed for the prediction of cooling rate and probability of carbide precipitation during quenching by finite difference method. Time-dependent heat transfer coefficient was adopted to achieve more precise results. Area ratio of carbide precipitation was measured by image analyzer to determine the critical point of carbide precipitation. Temperature-dependent critical cooling rate at that point was calculated by the developed numerical program. Finally, the probability of carbide precipitation on the whole area of specimen can be predicted by the proposed numerical program and the numerical result of a specimen was compared with the experimental result.
Virtual Mold Technique in Thermal Stress Analysis during Casting Process

Si-Young Kwak,Jae-Wook Baek,Jeong-Ho Nam,Jeong-Kil Choi,

材料科学技术学报 , 2008,
Abstract: It is important to analyse the casting product and the mold at the same time considering thermal contraction of the casting and thermal expansion of the mold. The analysis considering contact of the casting and the mold induces the precise prediction of stress distribution and the defect such as hot tearing. But it is difficult to generate FEM mesh for the interface of the casting and the mold. Moreover the mesh for the mold domain spends lots of computational time and memory for the analysis due to a number of meshes. Consequently we proposed the virtual mold technique which only uses mesh of the casting part for thermal stress analysis in casting process. The spring bar element in virtual mold technique is used to consider the contact of the casting and the mold. In general, a volume of the mold is much bigger than that of casting part, so the proposed technique decreases the number of mesh and saves the computational memory and time greatly. In this study, the proposed technique was verified by the comparison with the traditional contact technique on a specimen. And the proposed technique gave satisfactory results.
Effect of Silane Coupling Agent on the Flexural Property of Glass Fiber Reinforced Composite Film  [PDF]
Hye-Hyun Kim, Si-Young Kim, Dae-Hee Kim, Chae-Young Oh, Nam-Ju Jo
Journal of Materials Science and Chemical Engineering (MSCE) , 2014, DOI: 10.4236/msce.2014.210006
Abstract:

Transparent glass fiber reinforced composites films ware fabricated by UV light induced chemical crosslinking of composite materials consisting of glass fiber and UV curable resin in film state. In order to apply film to flexible device, excellent flexural property is required, then the delamination should not occurred between glass fiber and UV curable resin when film is bent. To minimize delamination and improve the interfacial adhesion at interface between glass fiber and UV curable resin, the γ-aminopropyl triethoxy silane and γ-glycid oxypropyl trimethoxy silane were applied for the surface treatment of glass fibers. Silanization of glass fiber surface was checked by scanning electron microscopy and the degree of delamination of composite film was confirmed through the bending test, ASTEM290-96a, used by haze meter.

Evaluation the Properties of Titanium Matrix Composites by Melting Route Synthesis

Bong-Jae Choi,Si-Young Sung,Myoung-Gyun Kim,Young-Jig Kim,

材料科学技术学报 , 2008,
Abstract: The main purpose of this study is an in-situ synthesis of (TiB TiC) hybrid titanium matrix composites (TMCs) by vacuum induction melting method and to verify its mechanical properties. The melting route was adopted to synthesize the commercial pure titanium (cp Ti) and granular boron carbide (B4C). The reinforcements, the fraction of 10 vol. pct, were formed by adding 1.88 wt pct B4C to cp Ti. After in-situ synthesis of TMCs, electron probe micro-analysis elemental mapping was carried out to confirm the distribution and shape of reinforcements. The cone-on-disk type sliding wear test was also done for the identification of TMCs. It is concluded that (TiB TiC) hybrid TMCs can be in-situ synthesized and has better wear properties than H13.
Epidural cement leakage through pedicle violation after balloon kyphoplasty causing paraparesis in osteoporotic vertebral compression fractures - a report of two cases
Si-Young Park, Hitesh N Modi, Seung-Woo Suh, Jae-Young Hong, Won Noh, Jae-Hyuk Yang
Journal of Orthopaedic Surgery and Research , 2010, DOI: 10.1186/1749-799x-5-54
Abstract: Osteoporotic vertebral compression fracture (OVCF) is the commonest complication of osteoporosis[1]. Over the past two decades, vertebroplasty was developed to stabilize OVCF without increasing morbidity and mortality associated with open surgery[2,3]. Diamond and colleagues. [4] noted that vertebroplasty for acute compression fracture was significantly better than nonoperative treatment in terms of pain relief, level of function, and hospital stay. However, complications related with vertebroplasty are not uncommon such as cement extravasation, pulmonary embolism, infection, epidural hematoma, systemic toxicity, and vertebral body fractures [5-17]. Among the commonest complications, cement extravasation has been estimated in 70% cases for vertebroplasty procedures [18,19]. Most of the time it is asymptomatic; however, disastrous complications causing paraparesis have been also reported in the literature [10,15,19].Kyphoplasty, as a modification of vertebroplasty, has theoretical advantages such as focal kyphosis correction and diminished risk of cement extravasation due to lower cement injection pressures [9,11,20-22]. Backer et al. [23] reported that out of 100 balloon kyphoplasties, overall cement leakage rate was 31%. Most leakages were anterior and superior; only 2% were posterior and most leakages were below 3 mm. The biomechanical principle of increasing anterior column load with progressing kyphosis leading to subsequent vertebral compression fracture has established the basic rationale for kyphoplasty [24]. Probably that is the reason for increasing use of kyphoplasty procedures for OVCF now a day. Even though kyphoplasty has significantly lower rates of cement extravasations than vertebroplasty [21], cement leakage may occur more frequently than originally appreciated, and often associated with significant morbidity [25]. There are numerous descriptions of significant spinal cord or cauda equina injuries associated with vertebroplasty procedures; however,
Evaluation of Alpha-case in Titanium Castings

Si-Young Sung,Bong-Jae Choi,Beom-Suck Han,Han-Jun Oh,Young-Jig Kim,

材料科学技术学报 , 2008,
Abstract: The alpha-case formation reactions between Ti and investment molds (Al2O3, ZrSiO4, ZrO2, CaO stabilized ZrO2) were evaluated in a plasma arc melting furnace. Regardless of thermodynamic approaches, there were distinct alpha-case formations. The reaction products were characterized by electron probe micro-analysis and transmission electron microscopy. The α-case generation between Ti and Al2O3 mold was not able to be explained by the conventional α-case formation mechanism, which is known to be formed by the interstitials, especially oxygen dissolved from mold materials. However, from our experimental results and thermodynamic calculations, it was confirmed that the c-case is formed not only by an interstitial element but also by substitutional metallic elements dissolved from mold materials. Our newly established α-case formation mechanism will surely lead to a variety of significant applications of the α-case controlled Ti casting.
Control of Crystallinity in Nanocrystalline Silicon Prepared by High Working Pressure Plasma-Enhanced Chemical Vapor Deposition
Jung-Dae Kwon,Kee-Seok Nam,Yongsoo Jeong,Dong-Ho Kim,Sung-Gyu Park,Si-Young Choi
Advances in Materials Science and Engineering , 2012, DOI: 10.1155/2012/213147
Abstract: The crystalline volume of nanocrystalline silicon (Si) films could be successfully controlled simply by changing the substrate scan speed at the high working pressure of 300?Torr. The Si crystalline volume fraction was increased from 30% to 57% by increasing the scan speed from 8 to 30?mm/s. When the Si film was prepared at a low scan speed (8?mm/s), Si crystals of size 5?nm grew homogeneously through the whole film. The higher scan speed was found to accelerate crystallization, and crystals of size up to 25?nm were deposited in the Si film deposited when the scan speed was 30?mm/s. 1. Introduction Nanocrystalline silicon (Si) films are mixed-phase materials containing a crystalline Si phase and an amorphous Si phase; they have attracted a lot of interests because of their superior properties, such as high stability against light soaking, high doping efficiency, and improved carrier mobility, compared to those of amorphous Si [1, 2]. Control of the crystalline volume is crucial because the Si crystallinity has a significant influence on the optical gap and conductivity of the materials [3]. For example, in a tandem Si thin film solar cell, the best performance is achieved with a material of low crystalline volume [4]. In contrast, for the gate of a thin film transistor (TFT), nanocrystalline Si with a high crystalline volume and uniform grain size is required for high mobility and good stability [5, 6]. The commonest method of obtaining nanocrystalline Si is plasma-enhanced chemical vapor deposition (PECVD) using a mixture of silane (SiH4) and hydrogen (H2) gases; hydrogenated nanocrystalline Si (nc-Si:H) is formed, and its crystallinity depends on the H2 flow rate or the plasma power [3, 7–9]. Hydrogen radicals are known to preferentially etch amorphous Si, and the exothermic heat generated during etching allows local recrystallization by chemical annealing [10, 11]. Here, we tried to develop a new method of fabricating homogeneous nc-Si:H films. We used a high working pressure plasma-enhanced chemical vapor deposition (HWP-PECVD) system with a cylindrical rotary electrode; this system is superior to conventional PECVD because it has the following features: a high deposition rate as a result of the high partial pressure of the reactive gas and a high plasma density by the very high frequency of 150?MHz; the ability to control the film uniformity because of the homogeneous distribution of reactants by the rotary electrode system; low bombardment damage because of the lower kinetic energy [12–16]. We were able to synthesize nc-Si:H films using HWP-PECVD
SIRT1 Regulates Thyroid-Stimulating Hormone Release by Enhancing PIP5Kγ Activity through Deacetylation of Specific Lysine Residues in Mammals
Sayaka Akieda-Asai,Nobuhiro Zaima,Koji Ikegami,Tomoaki Kahyo,Ikuko Yao,Takahiro Hatanaka,Shun-ichiro Iemura,Rika Sugiyama,Takeaki Yokozeki,Yoshinobu Eishi,Morio Koike,Kyoji Ikeda,Takuya Chiba,Haruyoshi Yamaza,Isao Shimokawa,Si-Young Song,Akira Matsuno,Akiko Mizutani,Motoji Sawabe,Moses V. Chao,Masashi Tanaka,Yasunori Kanaho,Tohru Natsume,Haruhiko Sugimura,Yukari Date,Michael W. McBurney,Leonard Guarente,Mitsutoshi Setou
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0011755
Abstract: SIRT1, a NAD-dependent deacetylase, has diverse roles in a variety of organs such as regulation of endocrine function and metabolism. However, it remains to be addressed how it regulates hormone release there.
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