• Korean Journal of Materials Research
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• v.2 no.6
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• pp.452-460
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• 1992

Effects of the microalloyed elements, temperatures and cooling rates on the strength and toughness of the medium carbon microalloyed hot forging steels obtained by air cooling(A.C.) method and the low carbon microalloyed forging steels by direct quenching(D.Q.) method were investigated. Combined additions of V+Nb produced the optimum combination of strength and toughness with ferrite-pearlite structure of the medium carbon steel by the A.C. method. 831MPa in UTS and 52.1J in toughness were obtained for 0.40c+0.12V+0.07Nb. It was martensite structure for the low carbon steel by the D.Q. method. The highest UTS and toughness obtained by Mo additions were 855MPa and 108j by 0.12C+0.10V+0.03Nb+1.13Mo respectively. Especially, the toughness of the low carbon steel was twice better than that of the medium carbon steel. 110$0^{\circ}C$was more appropriate than 120$0^{\circ}C$ for the reheating and forging temperature and 1.$2^{\circ}C$ /s was the best cooling rate from the viewpoint of the strength and toughness. Multiple regression analysis was used to quantify the influence of the microalloyed elements, temperatures and cooling rates on the strength, toughness, austenite grain size, and the pearlite interlamellar spacing.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.5
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• pp.429-436
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• 2014

This paper presents the seismic performance of a geometrically unsymmetrical reinforced concrete building considering torsional effect and material nonlinearity of concrete and steel. The reinforced concrete building is a structure for seismic performance evaluation in the SMART-2013 international benchmark program. Nonlinear constitutive models for concrete and steel were constructed, and their numerical performance was demonstrated by various local tests. Modal analysis showed that the first three natural frequencies and mode shapes were close to the experimental results from the SMART-2013 program. In the time history analysis for low-intensity seismic loadings, displacement and acceleration responses at sampling points were similar to the experimental results. In the end, nonlinear time history analysis was conducted for Northridge earthquake to predict the behavior of the reinforced concrete structure under high-intensity seismic loadings.

• Journal of the Korean Electrochemical Society
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• v.2 no.3
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• pp.156-162
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• 1999

Various types of iron oxide based materials as a cathode of lithium secondary battery have been prepared and their electrochemical characteristics have been also observed. In order to understand the fundamental characteristics of iron oxide electrode, three kinds of iron oxides such as iron oxides formed by direct oxidation of iron plate or iron powders and FeOOH powders were tested with cyclic voltammetry. The oxidation and reduction peaks due to the reaction of intercalation and deintercalation were not observed for the iron oxide prepared with iron plate and FeOOH powders. In case of iron oxide prepared from iron powders, only one reduction peak was observed. A layered form of $LiFeO_2$ was synthesized directly from $FeCl_3\cdot6H_2O,\;NaOH\;and\;LiOH$ and LiOH by hydrothermal reaction. The effect of NaOH on the electrode performance was examined. When increasing NaOH, it provides the electrode with less discharge capacity and efficiency, however, decreasing rate of discharge capacity became smaller. $LiFeO_2$ synthesized with the molar ratio of $NaOH/FeCl_3/LiOH$, 2/1/7 showed the largest capacity, but the discharging efficiency was sharply decreased after 30 cycles.

• Composites Research
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• v.12 no.6
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• pp.74-82
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• 1999

The static and fatigue characteristics of polyurethane foam cored sandwich structures are investigated. Three types of the specimens with the glass fabric faces and the polyurethane foam core are used; non-stitched. stitched, and stiffened sandwich specimen. Especially additional structural reinforcements with the twisted polyester and glass fiber for thickness direction are made to stitched sandwich structure panel to minimize the delamination of structure which is stitched the upper and lower faces through the core and the resin is impregnated Into stitched fiber with the characteristics of low viscosity of resin at resin flow temperature and cured together with during the curing process. Bending strength of stitched specimen which is 50 mm $50{\times}50{\;}mm$ pitched is improved by 50 % as com-pared with non-stitched specimen and stiffened specimen is improved 10 times more than non-stitched structure. After fatigue testing of $10^6$cycles by 20% of ultimate load under monotonic load, the bending fatigue strength of non-stitched specimen is decreased by 27% of monotonic bending strength, 39% for stitched structure and 20% for stiffened specimen. To verify the aging effect of polyurethane form core, Ultrasonic C-scanning equipment is used to detect the damage of skin laminate alone after fatigue test. From results of UT C-scan images, there is no defect that can be damaged occurred during fatigue test. It is concluded that the decrease of bending strength for foam cored sandwich specimen is caused by the decrease of stiffness due to the aging of polyurethane foam core during fatigue cycles.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.6
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• pp.33-39
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• 2002

Response Modification Factor(R-factor) approach is currently implemented to reflect inelastic ductile behavior of the structures and to reduce elastic spectral demands from earthquakes to the design level. However R factors were set empirically and simply based on the professional committee consensus on observed performance of building structures during past earthquakes. Consequently some major shortcomings linked to the current R factor approach have been pointed out. Using reinforced concrete intermediate moment-resisting frames(RC IMRFs), an analytical procedure is presented in this paper to establish R factor rationally. To this end, analytical R values were evaluated based on N2 Method and compared with the values recommended by IBC 2000. Overall, the analytical results correlated well with the code values. However the results also revealed that R factor might strongly depend on the system fundamental period. As evidenced by the interstory drift index(IDI) analysis results of this study, current R-factor based(or, Life Safety based) design tends to fail in fulfilling other implicit and hopeful performance objectives such as immediate Occupancy and Collapse Prevention. Performance based design(PBD) appears to be a promising approach to meet the multi level seismic performance objectives assigned to the building structures of nowadays.

• Economic and Environmental Geology
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• v.53 no.1
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• pp.87-98
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• 2020

The bird track fossil site in Haman Formation is divided into seven sedimental layers by the sedimentary structures, lithofacies and sequences. The bird tracks top on the highest layer, which includes ripple marks and suncracks. The layer has lithofacies with reddish grey siltstone and dark grey mudstone, alternately. As an analysis for the same rocks of the fossil site, physical properties show on mean values for 0.62% of absorption rate, 1.64% of porosity and 2.63 of specific gravity. Rock-forming minerals composed mainly of plagioclase, quartz, calcite, chlorite and mica. Meanwhile, we executed an experiments based on the petrography and weatherings to find a proper consolidants. In the experiments, the OH 100 reagent proved stable aspect and the lowest transition rate in terms of weight and chromaticity. Also, it showed the highest increase in ultrasonic velocity, improving the physical properties of the rocks. In the case of applying the OH 100 with antihygro, an swelling inhibitors on the sedimentary rocks, the chromaticity indicated an stable transition aspect. When it comes to the physical properties, the antihygro also decreases the porosity effectively. Thus, the most proper method for the fossil site of Haman Formation is to apply antihygro and OH 100 reagents since the rocks includes clay minerals that show swelling characteristics. However, this result is deduced from an indoor application experiments, leaving the necessity of verification how these reagents would affect the bird tracks site under the field condition.

• Economic and Environmental Geology
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• v.36 no.1
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• pp.1-8
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• 2003

This study was performed to measure expandabilities and coherent scattering domain sizes (CSDs) of bentonite samples from Campo and Yonil area, Korea, using X-ray powder diffraction (XRD), and to compare their experimental data with those of international standard bentonite samples (SAz-1, STx-1, and SWy-2). Most of Gampo and Yonil bentonite samples comprised randomly interstratified illite-smectite (R0 I-S), and their expandabilities ranged over 77-100%S$_{XRD}$ from the saddle/001 method. The interstratification deformed 001 peaks of EG-solvated samples (Mering's first principle), which prohibited us from adopting these peaks to measure CSDs using BWA (Bertaut-Warren-Averbach) method. CSDs of the bentonite samples with R0 I-S could be measured through dehydration at 30$0^{\circ}C$ after K-saturation, where the deformation originated from the interstratification could be removed effectively. Campo and Yonil bentonite samples showed that their mean CSDs ranged over 3.8-5.4 interlayers, and that their CSDs distributions were similar to those of Gonzales (STx-1) and Wyoming (SWy-2) bentonite samples.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2000.11a
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• pp.17-17
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• 2000

탄소섬유/에폭시 적충복합재는 경량성 및 비강도, 비강성이 우수해 최근 들어 항공기, 자동차, 우주선 등에 대한 적용이 급속도로 증가하고 있다. 그러나 적충복합재 구조물에 있어 최대 약점 중 하나는 적충된 면이 서로 떨어지는 충간분리가 발생 할 수 있다는 것이다. 본 논문에서는 탄소섬유/에폭시 적충복합재의 파괴특성을 향상시키기 위해 프리프레그 (prepreg)를 이온빔으로 표면처리하는 방법에 대해 연구하였다. 즉 프리프레그를 $Ar^+$ 이온도 움반응법에 의해 표면처리 하였으며 이를 적용, 열림모드 파괴특성을 검토하였다. 즉 표준 프리프레그와 표면처리 된 프리프레그를 이용 $0^{\circ}$ 단일방향 DCB(Double Cantilever Beam) 시편을 제작하였으며, 각각의 경우에 대하여 파괴시험을 수행하였다. 파괴시험으로부터 파괴 저항곡선(R-곡선)을 결정하여 이를 비교 검토함으로서 프리프레그의 표면처리가 파괴특성에 미치는 영향을 해석하였다. 본 연구를 통해 얻어진 결과를 요약하면 다음과 같다. 첫째, 층간분리 길이가 동일한 경우 표면처리한 경우의 컴플라이언스가 표면처리 하지 않은 경우에 비해 작게 나타남을 알 수 있었다. 둘째, 파괴하중 값은 컴플라이언스와 반대현상을 나타낸다. 즉 표면처리한 경우의 파괴하중 이 표면처리 하지 않은 경우에 비해 크게 나타남을 알 수 있었다. 셋째, 표면처리 한 시편의 경우 R-곡선이 향상됨을 알 수 있었다. 즉 표면처리 한 경우의 열림모드 파괴이성, $G_{Ic}$ 값은 표준 시편의 값보다 24% 높았다. 이는 프리프레그의 표면처리 가 충과 충간의 접착강도를 증가시키고 또한 탄소섬유와 에폭시 간의 계면력을 증가시킨데 기인하는 것으로 사려된다.되었으며, duty-on 시간의 증가에 따라 $Cr_2N$ 상의 형성이 점점 많아져 80% duty-on 시간 경우에는 거의 CrN과 $Cr_2N$ 상이 공존하는 것으로 나타났다. 또한 duty-on 시간이 증가할수록 회절피크의 세기가 증가하여 결정화가 더 많이 진행되어짐을 알 수 있었다. 마찬가지로 바이어스 펄스이 주파수에 다른 결정성의 변화도 펄스의 주파수가 증가할수록 박막이 결정성이 좋아지고 $Cr_2N$ 상이 쉽게 형성되었다. 증착 진공도에 따른 결정성은 상대적으로 질소의 농도가 높은 낮은 진공도에서는 CrN 상이 주로 형성되었으며, 반대로 높은 진공도에서는 $Cr_2N$ 상이 많이 만들어졌다. 즉 $1.3{\times}10^{-2}Torr$의 증착 진공도에서는 CrN 상만이 보이는 반면 $9.0{\tiems}1-^{-2}Torr$ 진공도에서부터 $Cr_2N$ 상이 형성되기 시작하여 $5.0{\tiems}10^{-2}Torr$ 진공도에서는 두개의 상이 혼재되어 있음을 알 수 있었다. 박막의 내마모성을 조사한 결과 CrN 박막의 마찰 계수는 초기에 급격하게 증가한 후 0.5에서 0.6 사이의 값으로 큰 변화를 보이지 않았으며, $Cr_2N$ 박막도 비슷한 거동을 보였다.차 이, 목적의 차이, 그리고 환경의 의미의 차이에 따라 경관의 미학적 평가가 달라진 것으로 나타났다.corner$적 의도에 의한 경관구성의 일면을 확인할수 있지만 엄밀히 생각하여 보면 이러한 예의 경우도 최락의 총체적인 외형은 마찬가지로 $\ulcorner$순응$\lr

• Economic and Environmental Geology
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• v.24 no.3
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• pp.233-244
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• 1991

A biotite that substantially altered to chlorite and vermiculite in hornblende gneiss from Cheonyang, Korea, has been investigated with electron microprobe analysis. The data show the general variational trends of Ti and K-leaching with increased weathering. However, the chloritization is characterized by Si- conservative reaction and relatively dramatic increase of Al-for-(Fe+Mg) octahedral substitution, whereas the vermiculitization is characterized by total Mg-conservative and Ca-enriching exchange reaction. In the initiating stage the vermiculitization proceeded in a continuous decrease of the Al-for-Si tetrahedral substitution and an increase of the Al-for-(Fe+Mg) octahedral substitution, supporting the currently accepted weathering process. But it differs in the late stage, in which AI(IV) and Fe increase significantly. Recalculations of the structural formular for vermiculite on the basis of several assumptions indicate that the oxidation of Fe is necessary for vermiculite to form the reasonable strutural formular. The relative timing of the oxidation of Fe probably occurs in the late stage, supported by the substantial increase of the Al-for-Si tetrahedral substitution.

• Journal of Digital Convergence
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• v.16 no.12
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• pp.77-86
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• 2018

This study was carried out by using the concentration index calculation method from 1996 to 2016 by using the household trend survey data to confirm the difference of income transfer income and inequality in public transfer income. The main results are as follows. First, the public transfer income concentration index in 1996 was concentrated on the high income group with +0.2774, but since 2009, the concentration index has been negative (-), which has concentrated on the low income group. However, the effect of redistribution of income was small. Second, the average public transfer income of low - income households increased significantly while the number of high income earners decreased. It is gradually improving that public transfer income did not play a role in the improvement of income inequality. Third, public transfer income has been continuously increasing in all income classes, and the rate of increase is low in the low income class and slow in the high income class, so the public transfer income of the low income class is higher than that of the high income class. In sum, the inequality of public transfer income by income class in Korea is gradually improving, but it is not considered to be a level that can improve the inequality between income groups.