• 한국해양공학회지
• /
• 제21권3호
• /
• pp.71-76
• /
• 2007

Recently, many industries have been employing the application of laser beam welding, due to the resulting high welding quality, such as smaller width of melting and heat affective zone, smaller welding deformation, and fine grains of weldment, compared to arc welding. However, in order to appropriately utilize this welding process with steel structure, the characteristics of welding residual stresses and fracture toughness in welded joints are to be investigated for reliability. Therefore, in this study, the mechanical properties of weldments by arc and laser welding are investigated using FEM to confirm the weldability of laser welding to the general structural steel (HT50). The Charpy impact test and 3-points bending CTOD test are carried out in the range of temperatures between $-60^{\circ}C\;and\;20^{\circ}C$, in order to understand the effect on the fracture toughness of weldments. From the research results, it has been found that the maximum residual stress appears at the center of plate thickness, and that the fracture toughness is influenced by strength mis-match.

• Ocean and Polar Research
• /
• 제33권1호
• /
• pp.1-11
• /
• 2011

This study describes measurements of fast ice recorded on May 23, 2009, in Kongsfjorden (translated as 'Kongs Fjord'), an inlet on the west coast of Spitsbergen in the Svalbard Archipelago. Seasonal fast ice is an important feature for Svalbard fjords, both in relation to their physical environment and also the local ecosystem, since it grows seaward from the coast and remains in place throughout the winter. Ice thickness, snow, ice properties, and wind speed were measured, while SAR (Synthetic Aperture Radar) data was observed simultaneously observed two times from ALOS-PALSAR (L-band). Measured ice thickness was about 25-35 cm while the thickness of ice floe broken from fast ice was measured as 10-15 cm. Average salinity was 1.9-2.0 ppt during the melting period. Polarimetric data was used to extract H/A/alpha-angle parameters of fast ice, ice floe, snow and glacier, which was classified into 18 classes based on these parameters. It was established that the area of fast ice represents surface scattering which indicates low and medium entropy surface scatters such as Bragg and random surfaces, while fast ice covered with snow belongs to a zone of low entropy surface scattering similar to snow-covered land surfaces. The results of this study will contribute to various interpretations of interrelationships between H/A/alpha parameters and the wave scattering Phenomenon of sea ice.

• 지질공학
• /
• 제18권1호
• /
• pp.7-16
• /
• 2008

석회암지역은 외부의 압력에 의한 파쇄대와 용해성공동 등과 같은 지질학적인 결함을 대부분 갖고 있다. 특히, 장대교량을 건설할 경우 지질학적인 결함을 갖고 있는 석회암공동의 처리는 꼭 필요하다. 석회암 공동에서 기초의 침하량을 줄이고 지반을 보강하기 위한 대책공법으로 고압분사주입공법이 많이 활용되고 있다. 그러나 고압분사주입공법은 석회암공동에 대한 보강공법으로 활용되어 왔으나 연구실적과 기술적인 자료의 축적이 부족한 편이다. 그러므로 본 논문은 고압분사주입공법에 의하여 보강된 석회암공동 구간에 대하여 강도특성과 변형특성에 대한 연구결과를 제시하였다. 그리고 하중전이시험이 수반된 정재하시험에 의하여 지지력특성도 논의하였다.

• 한국주조공학회지
• /
• 제8권3호
• /
• pp.287-295
• /
• 1988

The experiment was carried out for the purpose of studying the carburization of pure iron ingot and sintered iron powder by solid carbon in the atmosphere of CO gas. The volocity of carburization was estimaed by the diffusion coefficient D calculated by carburization equation. The results obtained were as follow: 1. The higher the carburization temperature, carburization depth and carbon concentration were increased, and the melting zone which had $2.8{\sim}3.4%C$ at the $3{\sim}4mm$ from interface of carburization was formed at $1300^{\circ}C$. 2. The main carburization mechanism of pure iron ingot and the sintered iron powder were proceeded by CO gas up to $1100^{\circ}C$, solid carbon over than $1300^{\circ}C$, respectively. 3. The main carburization mechanism of pure iron ingot at $1200^{\circ}C$ was proceeded by solid carbon, and sintered iron powder was proceeded bs CO gas, however, in case the reaction time, the carburization was proceeded by solid carbon over than 5hrs. 4. The diffusion coefficient D of carbon were $0.559{\times}10^{-6}cm^2.sec^{-1}$ at $1100^{\circ}C$, $0.237{\times}10^{-6}cm^2.sec^{-1}$ at $1200^{\circ}C$, $0.087{\times}10^{-6}cm^2.sec^{-1}$ at $1300^{\circ}C$, in case of pure iron ingot carburized. 5. The diffusion coefficient D of carbon were $0.124\;cm^2.sec^{-1}$ at $1100^{\circ}C$, $0.102\;cm^2.sec^{-1}$ at $1200^{\circ}C$, $0.480\;{\times}10^{-6}cm^2.sec^{-1}$ at $1300^{\circ}C$, in the case of sintered iron carburized at the pressuring $4ton\;/\;cm^2$.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2001년도 하계학술대회 논문집
• /
• pp.624-627
• /
• 2001

Two kinds of Nd$_{1+x}$Ba$_{2-x}$Cu$_3$O$_{7-{\delta}}$, the sintering samples and zone melting samples, were heat treated under pure Ar at 95$0^{\circ}C$. The substitution of Nd ion for Ba ion in the Nd$_{1+x}$Ba$_{2-x}$Cu$_3$O$_{7-{\delta}}$ before and after the heat treatment were investigated by XRD. In order to know the effects of the heat treatment, the T$_{c}$ and J$_{c}$ of samples with the heat treatment and those without the heat treatment by Ar were comparatively studied. The results show that the substitution of Nd for Ba decreased, T$_{c}$, and J$_{c}$ increased after the treatment under Ar at 95$0^{\circ}C$. The Nd$_{1+x}$Ba$_{2-x}$Cu$_3$O$_{7-{\delta}}$ samples were oxygenated under pure oxygen at 30$0^{\circ}C$. From the XRD pattern it was found that the sample with x< 0.4 could transfer from tetragonal phase to orthorhombic phase after the oxygenation, but the sample with x>0.4 could not make the phase transition even after a long time oxygenation.ion even after a long time oxygenation.ation.n.ation.ation.

• Journal of Welding and Joining
• /
• 제27권3호
• /
• pp.73-79
• /
• 2009

This present paper investigated the mechanical properties and the microstructures of each penetration shapes classifying the conduction shape area and the keyhole shape area about electron beam welded 120(T)mm thick plated aluminum 5052 112H. As a result the penetration depth is increased linearly according to the output power, but the aspect ratio is decreased after the regular output power. In the conduction shape area, the Heat affected zone is observed relatively wider than the keyhole shape area. In the material front surface of the welded specimen, the width is decreased but the width in the material rear surface is increased. After the measuring the Micro Vikers Hardness, it showed almost similar hardness range in all parts, and after testing the tensile strength, the ultimate tensile strength is similar to the ultimate tensile strength of the base material in all the specimens, also the fracture point was generated in the base materials of all the samples. In the result of the impact test, impact absorbed energy of the Keyhole shape area is turned up very high, and also shown up the effect about four times of fracture toughness comparing the base material. In the last result of observing the fractographs, typical ductile fraction is shown in each weld metal, and in the basic material, the dimple fraction is shown. The weld metals are shown that there are no other developments of any new chemical compound during the fastness melting and solidification.

• 한국결정성장학회지
• /
• 제1권2호
• /
• pp.23-33
• /
• 1991

Mn-Zn Ferrite는 단결정을 성장하기 위하여 용융하는 동안 불균질 용융과 ZnO휘발의 고유특성을 갖는 재료이다. 그 결과로, 결정성장축을 따라 양이온의 분포가 불균일 하게 된고 또한 기존의 Bridgman법에서는 도가니내에서 용융대가 장시간 유지됨으로써 백금입자가 결정안으로 침입하게된다. 이들은 훼라이트의 자기적 성질을 저하시키는 성질을 갖고 있다. 그러나 새로운 성장법에서는 이러한 단점들을 극복하고 양질의 단결정을 얻기 위하여 결정성장 인자들의 관계를 고찰하였으며 그 인자들은 다음과 같다 : 도가니내의 melt 높이, melt의 표면장력과 밀도, 계면에서의 melt거동, 도가니와 고액계면의 형상, 원료공급속도, 결정성장속도. 아울러, 성장된 결정의 조성을 분석하였을 때 초기조성과 비교하여 $\textrm{Fe}_2\textrm{O}_3$ 1.5 mol%, MnO, Zn 2.0 mol% 이내로 조성 변동은 각각 억제되었고 성장결정면 (110)에서 화확적인 etching 법을 이용하여 광학현미경을 통해 결정내부등을 관찰하였으며, 자기적 특성등을 측정하였다.

• 자원환경지질
• /
• 제29권4호
• /
• pp.455-470
• /
• 1996

Mesozoic granitic rocks in the Korean peninsula contain $H_2$, $CH_4$, CO and rare $C_2H_6$. The Jurassic Daebo granites mostly belonging to the ilmenite series are predominated in $CH_4$. Meanwhile, the magnetite series Bulguksa granites of Cretaceous age in the Kyongsang basin and Okchon zone are relatively enriched in $CO_2$. The older granites have a wide variation of $CH_4/CO_2$ ratios (0.1~1.0) compared to those of the younger ones (0.1~0.5). This characteristics of gas compositions suggest that the Jurassic granites are principally derived from the partial melting of metasedimentary rocks with much reducing materials in the lower continental crust. On the other hand, the mantle source granitic magmas might be responsible for the Cretaceous granites characterized by dominant and homogeneous $CO_2$ gas compositions. Liquid-vapor homogenization temperatures of quartz in the Jurassic and Cretaceous granites range from 108 to $539^{\circ}C$ (av. $324^{\circ}C$) and 160 to $556^{\circ}C$ (av. $358^{\circ}C$), respectively. Their salinities are between 0.2 and 16.3 wt.% NaCl for the Jurassic granites and 0.4, and 15.6 wt.% NaCl for the Cretaceous ones. Fluid inclusions with solid daughter minerals lying on or near the halite equilibrium curve represent inclusion fluids from the magmatic stage. The type I and II fluid inclusions which are plotted apart from the equilibrium curve are considered to trap in late hydrothermal alteration stage with a increasing influx of metedric water.

• 센서학회지
• /
• 제13권6호
• /
• pp.411-416
• /
• 2004

In the international temperature scale of 1990 (ITS-90), standard platinum resistance thermometer (SPRT) is a defining standard thermometer used in the temperature range from 13.8033 K to $961^{\circ}C$. Uncertainty of SPRT is about several mK and uncertainty of defining fixed points of the ITS-90 which is used for calibrating SPRT is about several tenth of mK. Above $0^{\circ}C$. the defining fixed points are gallium melting point and indium, tin, zinc, aluminium and silver freezing points which are all realized using an electric furnace or a liquid bath. To realize freezing point of tin ($231.928^{\circ}C$) and zinc ($419.527^{\cir}C$), two 3-zone furnaces which have 3 electric heaters were manufactured. Temperature gradient of the constructed furnaces were tested. Uncertainty caused by temperature gradient of furnace and immersion effect of SPRT in the sealed-type freezing point cells were evaluated 0.038 mK for tin freezing point and 0.036 mK for zinc freezing point.

• 한국결정성장학회지
• /
• 제6권4호
• /
• pp.532-542
• /
• 1996

Floating zone(FZ)법으로 육성하고 annealing한 undoped $LiNbO_3$ 단결정 및 MgO 또는 ZnO를 첨가한 $LiNbO_3$ 단결정의 전기적,광학적 특성을 조사하였다. 전기전도도, 유전율 및 전이온도, 전기.기계결합계수등의 전기적 특성과 광투과율, 굴절율 등의 광학적 특성을 측정하였으며, 비선형 광학특성의 척도라 할 수 있는 비선형 굴절율을 이론적으로 계산하였다. Undoped $LiNbO_3$ 단결정과 MgO 또는 ZnO를 첨가한 $LiNbO_3$ 단결정의 전기적, 광학적 특성을 비교함으로서 MgO 또는 ZnO의 첨가가 $LiNbO_3$ 단결정의 전기적 및 광학적 특성에 미치는 영향을 조사하였다.