• 한국표면공학회지
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• 제54권2호
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• pp.62-70
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• 2021

Al2024 aluminum alloy specimens were exposed to atmospheric conditions for maximum 24 months and analyzed by electron microscopes to characterize their corrosion behavior and oxide film characteristics. As the exposure time increased from 12 months to 24 months, the number of pitting sites per 1 mm² increased from ~100 to ~200. The uniform oxidation (or non-pitting) region of the 12-month exposure specimen showed 30~120 nm thick oxide layer, whereas the 24-month exposure specimen showed 170~200 nm thick oxide with the local oxygen penetration region up to 1 ㎛ deep. There was no local corrosion area observed in the 12-month exposure specimen except pitting. However, in the 24-month exposure specimen, local oxygen penetration region was observed beneath the uniform oxide layer and near the pitting cavity. Al2024 showed two times thicker uniform oxide layer but much shallower local oxygen penetration region than Al1050, which appears to be related to low Si concentration. Further research is needed on the effects of Mg segregation near the tip of the oxygen penetration region.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2013년도 추계 학술논문 발표대회
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• pp.173-174
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• 2013

In this study, the tensile properties of sealants by heat deterioration were measured and analysed to gather the basic data of sealant because these studies do not have been investigated in Korea. Most general one-component silicone sealants were used and test specimen was I-type. The test parameters are sealant types which have different density and heat deterioration time in 80℃. As a result, the rat of reduction in area by heat deterioration was considerable increased at SR-A compared with SR-B. The tensile properties by heat deterioration decreased at SR-A because the specimen by deterioration occurred adhesive failure before tensile test. However, SR-B specimen was increased at maximum tensile stress but decreased at elongation in maximum tensile stress. Also, Maximum principal stress was measured at the edge of specimen by FEM simulation in order to find out failure points.

• 한국재료학회지
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• 제12권10호
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• pp.776-783
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• 2002

Austenitic stainless steel (STS304) has been carburized using glow discharge plasma and its microstructure, wear resistance and corrosion property have been investigated. A repeat boost-diffuse carburizing was used as an effective plasma carburizing method. The effective case depth of the plasma carburized specimens was increased with the carbon concentration at the surface area. The specimens prepared by 3 hours plasma carburizing under $600^{\circ}C$ did not have the standard hardness for the effective case depth, but the specimen prepared by 11 hours plasma carburizing at $500^{\circ}C$ had nearly the same hardness with the specimen plasma carburized for 3 hours at $800^{\circ}C$. The wear resistance increased with temperature but the corrosion properties of the specimens prepared over $600^{\circ}C$ decreased rapidly due to the grain boundary sensitization. However, the specimen plasma carburized for 11 hours at $500^{\circ}C$ had nearly the same wear resistance with the specimen plasma carburized for 3 hours at $800^{\circ}C$ without deterioration of corrosion property. This could be resulted from the fact that the microstructure of the specimen plasma carburized for 11 hours at $500^{\circ}C$ was composed of martensite and austenite, because a partial martensite transformation was occurred only in the specimen plasma carburized for 11 hours at 50$0^{\circ}C$.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.581-584
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• 2008

본 연구에서는 판상-링형 구속시험방법의 유효성 평가를 위하여 그 특성을 국내.외에서 제안된 콘크리트 구속수축시험방법과 비교하여 간편하고 정량적인 수축균열 평가방법의 개발을 위한 기초자료를 제시하고자 하였다. 판상-링형 구속시험방법의 적정 시험체 치수를 검토하기 위하여 시험체 내부링 직경 100, 150 및 200mm, 시험체 높이 30 및 50mm에 대하여 온도 20${\pm}$3$^{\circ}$C, 습도 60${\pm}$5%의 항온항습조건에서 양생 후 마이다스 프로그램을 이용한 3D Solid 요소의 수치 해석, 건조수축변형, 구속수축응력, 균열면적 및 균열 포인트 측정 등 콘크리트의 구속수축균열 특성을 평가하였으며, 그 결과 콘크리트 링 시험체 내부 링 직경 최소 150mm이상, 높이 50mm에서 변별력 있는 평가가 가능한 것으로나타났다. 본 연구를 바탕으로 향후, 판상-링형 구속시험방법에 있어서 온도, 풍속 등의 환경조건 및 배합조건에 따른 콘크리트의 구속수축균열특성에 관한 연구가 필요할 것으로 사료된다.

• Restorative Dentistry and Endodontics
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• 제18권2호
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• pp.431-445
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• 1993

The purpose of this study was to observe corrosion characteristics of six dental amalgams and was to analyse corrosion products electrochemically. After each amalgam alloy and Hg was triturated as the direction of the manufacturer by using mechanical amalgamator, the triturated mass was inserted into the cylinderical metal mold ($12{\times}10mm$) and was condensed with 160kg/$cm^2$ by using the hydrolic press. The specimen was removed from the mold and was stored at room temperature for 1 week, and was polished with amalgam polishing kit. The anodic and cathodic polarization curve was obtained by using cyclic voltammetric method with 3-electrode potentiostat in saline for each amalgam and Ag, Sn, Cu plate specimen at $37{\pm}0.5^{\circ}C$. The potential sweep range was -1.7V~0. 4V(vs SCE) in working electrode and scan rate was 50mV/s and the exposed surface area of each specimen to the electrolytic solution was $0.79cm^2$. The results were as follows. 1. In anodic-cathodic polarization curve of amalgam specimens, two anodic current rising areas and two cathodic current peaks were obtained at the low Cu amalgam(CF, CS) specimen and three anodic current rising areas and three cathodic current peaks were obtained at the high Cu amalgam (TY, DS, HV) specimen. 2. As this compared with the anodic and cathodic current peak potentials of Sn, Cu and Ag specimen, the first cathodic current peak I c was caused by the reduction of divalent tin salt, second cathodic current peak IIIc results from the reduction of quadravalent tin salt, and third cathodic current peak me results from the reduction of copper salt. 3. As reverse potential sweeping was done repeatedly, anodic current was decreased slightly in all amalgam specimens.

• 한국추진공학회지
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• 제5권1호
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• pp.42-48
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• 2001

지난 20년 동안 인장하중과 굽힘 하중 상태에서 복합재료 적층판의 크기효과에 관한 많은 연구가 수행되었으며, 시편의 크기를 증가함에 따라 복합재 적층판의 강도가 저하되는 경향은 잘 알려져 있다. 그러나, 복합재 압축시험의 어려움으로 인해 압축하중 상태에서 시편의 파괴강도에 대한 크기효과에 관한 연구는 거의 수행되지 않았다. 본 연구에서는 홀을 갖는 복합재의 압축 강도에 대한 크기 효과를 고찰하기 위해 T300/924C, $>[45/-45/0/90]_{3S}$를 사용하였으며, 시편의 크기 변화를 위해 2차원면적 변화(시편의 폭 및 길이 변화)를 고려하는 평면 스케일링 방법을 사용하였다. 실험 결과는 유한폭을 가지는 평판에 대한 명확한 홀 크기 효과를 보였을 뿐만 아니라, 같은 a/W(홀 직경/시편 폭)를 갖는 시편에서도 크기 효과를 확인할 수 있었다. 반면에, 홀이 없는 시편은 명확한 강도 크기 효과를 보이지 않았다.

• 한국화재소방학회논문지
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• 제29권1호
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• pp.12-18
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• 2015

본 연구에서는 실내장식 및 가구류 등에 이용되고 있는 편백루바와 파티클보드를 이용하여 방염처리 방법에 따른 방염성능 및 연소특성을 비교하는 실험을 하였다. 편백루바의 방염성능검사 결과 진공가압처리를 이용하여 난연수지를 주입한 편백루바가 표면에 염화고무수지 성분의 방염도료처리를 한 편백루바 보다 탄화면적은 9.55%, 탄화길이에서는 22.91% 우수한 것으로 나타났으며, 파티클보드는 파티클보드에 방염필름을 부착한 시편이 비방염필름을 부착한 시편보다 탄화면적 40.10%, 탄화길이에서는 43.40% 우수한 것으로 파악 되었다. Cone calorimeter를 이용한 연소특성 결과 편백루바 표면에 방염도료 처리를 한 시편이 진공가압처리를 이용한 난연수지 주입방식의 편백루바 보다 착화가 빨리 발생하였고, 총방출열량에서는 진공가압처리를 이용한 난연수지 주입방식의 편백루바가 $68.2MJ/m^2$, 편백루바 표면에 방염도료 처리를 한 시편이 $111.52MJ/m^2$을 나타내었으며, 파티클보드의 경우 착화시간에서는 미소한 차이를 보인 반면 총 방출열량에서는 파티클보드에 방염필름을 부착한 시편이 $90.1MJ/m^2$, 비방염필름을 부착한 시편은 $107.6MJ/m^2$의 총열방출량을 나타내었다.

• Ocean and Polar Research
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• 제32권2호
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• pp.123-135
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• 2010

Around Tongyeong coasts which located in southern coast of Korea composed to the complex coastal line and scattered by small islands. It also has been distributed to a complicated bathymetric structure by several types of channels. This study carried to analyze the spatial characteristics of macrobenthic community and benthic environmental variance on sub-tidal area based on multivariate statistics tools. Sediment composition varied from muddy sand to mud, and along the channels, it composed to a heterogeneous bottoms mixed by shell fragment, cobbles and mud. Organic contents on the surface sediment varied 1.1-3.9%. Total of 272 species, $33,349\;ind./m^2$ of macrobenthos identified in all of sample area. Polychaetes also prevailed among the specimen. L. longifolia, P. pinnata dominated based on density. Considering on the biomass, echinoderm S. lacunosa, A. tricoides listed. Closer to the coastal area, the density and diversity were higher. Community structure based on cluster analysis was discriminated into three groups. Each group was also characterized by geographical state such as depth, sediment composition. In addition, when applied to the bathymetric data, the channel, which composed to the mixed sediment, made a role of limited factor which characterized to benthic community. Because the specimen around the channel have been affected on the diverse sediment mixture. Most of benthic studies in the southern coast of Korea focused to the condition of benthic organic pollution spatially, because along the coast, it also developed a aquaculture ground and industrial complex. But, as results, most of the area, it turn out the less polluted areas nevertheless similar environment situation. It supposed that benthic community affect to the bottom sediment composition by physical characteristics.

• Steel and Composite Structures
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• 제21권5호
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• pp.1017-1029
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• 2016

When a welded circular hollow section (CHS) tubular joint is subjected to brace axial loading, failure position is located usually at the weld toe on the chord surface due to the weak flexural stiffness of the thin-walled chord. The failure mode is local yielding or buckling in most cases for a tubular joint subjected to axial load at the brace end. Especially when a cyclic axial load is applied, fracture failure at the weld toe may occur because both high stress concentration and welding residual stress along the brace/chord intersection cause the material in this region to become brittle. To improve the ductility as well as to increase the static strength, a tubular joint can be reinforced by increasing the chord thickness locally near the brace/chord intersection. Both experimental investigation and finite element analysis have been carried out to study the hysteretic behaviour of the reinforced tubular joint. In the experimental study, the hysteretic performance of two full-scale circular tubular T-joints subjected to cyclic load in the axial direction of the brace was investigated. The two specimens include a reinforced specimen by increasing the wall thickness of the chord locally at the brace/chord intersection and a corresponding un-reinforced specimen. The hysteretic loops are obtained from the measured load-displacement curves. Based on the hysteretic curves, it is found that the reinforced specimen is more ductile than the un-reinforced one because no fracture failure is observed after experiencing similar loading cycles. The area enclosed by the hysteretic curves of the reinforced specimen is much bigger, which shows that more energy can be dissipated by the reinforced specimen to indicate the advantage of the reinforcing method in resisting seismic action. Additionally, finite element analysis is carried out to study the effect of the thickness and the length of the reinforced chord segment on the hysteretic behaviour of CHS tubular T-joints. The optimized reinforcing method is recommended for design purposes.

• 한국건축시공학회지
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• 제2권2호
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• pp.129-134
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• 2002

The strength and durability of concrete are affected by various factors such as the quality of material, mixing ratio, construction, the method of cure, time elapsed. the condition of test and etc., it is very difficult to pre-estimate the strength of concrete with the use of experimental specimen. The domestic standard of specimen cylindrical type and its sizes are both l0cm$\times$20cm and 15cm$\times$30cm, which are prescribed in KS F2405, and the loading speed is prescribed to test with 2~3kgf/$\textrm{cm}^2$ per second. The loading speed should have great effect on the compressive strength, but in reality in the construction site sometimes the loading speed is applied so dubiously that the value of the compressive strength can be unreliable. And the cross sectional area of a specimen should be level and smooth, otherwise it can be broken at a lower stress than the real strength through the eccentric or intensive working of the load. Capping should be carried out in order to measure the strength correctly. And used for capping are various materials such as capping compound, cement glue, plaster, mechanical grinding and etc. In this study, therefore, I have carried out an experiment on the relationship among the loading speed, the ratio of height to diameter of specimen, the method of capping, and the compressive strength, for the efficient quality control of concrete structures. So this study has been purposed to provide some basic data that can be used effectively at construction sites.