• 한국전기전자재료학회논문지
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• 제33권6호
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• pp.450-453
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• 2020

In this study, ZnO:Ga thin films were fabricated on a glass substrate using various Ar flows by an RF magnetron sputter system at room temperature. The dependencies of Ar flow on different properties were investigated. An appropriate control over the Ar flow led to the formation of a high-quality thin film. The ZnO:Ga films were formed as a hexagonal wurtzite structure with high (002) preferential orientation. The films exhibited a typical columnar microstructure and a smooth top face. The average transmittance was 85~89% within the visible area. By decreasing the Ar flow, the sheet resistance was decreased due to an increase in the grain size and a decrease in the root mean square roughness. The lowest sheet resistance of 86 Ω/□ was obtained at room temperature for the 40 sccm Ar flow.

• 한국결정성장학회지
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• 제10권2호
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• pp.122-127
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• 2000

불규칙 입자형성을 갖는 Ce-TZP와 알루미나가 분산된 Ce-TZP 세라믹스를 세라아 도핑조선과 열처리 조건을 변화시켜 제조한 다음, 미세구조를 관찰하였다. 제조된 시편들은 상대밀도가 99% 이상인 고밀도의 소결체였으며, 정방정 및 입방정상 지르코니아 입자로 구성되었다. 도핑하지 않거나 소결만 시킨 시편의 경우 직선적인 입계와 정상적인 입자형성을 나타낸데 비하여 세리아를 침적법으로 도핑한 후 고온으로 열처리한 시편에서는 확산구동 입계이동이 일어나 입계 및 입자형성이 불규칙하였으며. 이러한 Ce-TZP에서는 입자당 평균 입계같이 정상입자에 비하여 크게 증가하였다. 알루미나를 분산시켜 소결한 {{{{ { Al}_{2 }{ O}_{3 } }}}}/Ce- TZP 시편의 경우, 알루미나 입자에 의해서 입성장이 크게 억제되었고, 세리아를 도핑한 후 소결과 열처리를 행한 {{{{ { Al}_{2 }{ O}_{3 } }}}}/Ce-TZP에서는 불규칙 입자형상이 형성되면서도 입성장이 억제되어 입자크기에 비하여 입계면적이 크게 증가하였다. 분산된 알루미나 입자들은 소결과 열처리 과정 중 입자크기가 증가하였고, 열처리 동안 많은 입자들이 입계에서 입내로 위치가 변화하였다. 정상적인 입자형성을 갖은 시편에서는 균열진전시 입계파괴가 주로 일어났으나 불규칙 입자형성을 갖는 시편에서는 주로 입내파괴가 관찰되었다.

• 한국지형학회지
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• 제25권3호
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• pp.43-55
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• 2018

This study aimed to identify different sedimentary environments of Gochang coast according to geomorphic conditions of each bore hole. To achieve the aim, this study utilized the classification of sedimentary environmental conditions of surface sediment, which was based on grain size distribution characteristics.In other words, three sedimentary environmental conditions ofsandy flat + sand beach, coastal sand dune and weathered bedrock soil, which were distinguished based on grain size distribution characteristics of mean-sorting for surface sediments, were applied to the sediments of bore holes. Four sedimentary environments could be identified in Gochang coast. First, the lake sedimentary environment originated from terrestrial sediments seems to have been dominated by weathered bedrock soil that the surface flow has deposited in a coastal wetland or a boundary, which is affected by the sea. Second, the lake sedimentary environment that is little affected by coastal sand dunes is located at the center of a valley, which is connected to the land, and the dune slack of Saban-ri. The surface flow of weather bedrock soil is the main source of deposits. However, there seems to have been a temporary influence of the sea. Third, the lake sedimentary environment that is strongly affected by coastal sand dunes is located at the dune slack of Yeongjeong-ri. This environment shows traces of a change from a coastal sand dune into the dune slack. Finally, the coastalsand dune sedimentary environment, which wasinvestigated by boring the current coastal sand dune, shows a temporary influence of the land but seems to have maintained the overall stability. Consequently, this study demonstrated that the grain size distribution characteristics of the present surface sediments could be effectively applied to identify the sedimentary environments of the paleo bore hole sediments. In addition, the paleo change of sedimentary environment could also be identified in many places of Gochang coast. If the results of this study are combined with the age dating and geochemical analysis in future works, the paleo environmental change in Gochang coast will be restored more precisely.

• 한국분말재료학회지
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• 제3권4호
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• pp.271-278
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• 1996

In this study, the effect of the transition elements on the microstructure and mechanical properties of rapidly solidified Al-Mg-X alloys was investigated. As a result of the rapid solidification processing, fine equiaxed grains with a mean diameter of 2 $\mu$m were observed in these alloys. Many fine particles were found to be distributed rather homogeneously throughout the matrix with relatively large particles occasionally at grain boundaries. The ultimate tensile strengths of Al-Mg-X alloys were found to decrease rather remarkably at 150 $^{\circ}C$ without the gain of the ductility at 150 $^{\circ}C$, which may result from segregation of $\beta$ ($Al_{3}Mg_{2}$) precipitates. Fine dimples were observed on the fracture surfaces for all alloy systems and the variation of the size and shape of dimples was not observed upon alloy systems. The ductility at 530 $^{\circ}C$ was found to be ~100%, suggesting that grain boundary sliding did not contribute to ductiliy despite he grain size stabilization. The absence of superplastic behavior may be associated with low boundary misorientation in rapidly solidified Al-Mg-X alloys.

• 소성∙가공
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• 제10권4호
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• pp.338-346
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• 2001

Evaluation of microstructural changes is important for process control during open die forging of heavy ingots. The control of forging parameters, such as shape of the dies, reduction, temperature and sequence of passes, is to maximize the forging effects and to minimize inhomogeneities of mechanical properties. The hot working die steel is produced by using the multistage open die forging. The structure is altered during forging by subsequent Precesses of plastic deformation, recrystallization and grain growth. A numerical analysis using an rigid visco-plastic finite element model was performed to predict microstructural evolution of hot working die steel.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.131-135
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• 2001

Evaluation of microstructural changes during open die forging of heavy ingots is important for process control. The objective of the control of forging parameters, such as shape of the dies, reduction, temperature and sequence of passes, is to maximize the forging effects md to minimize inhomogeneities of mechanical properties. The hot working die steel is produced by using the multistage open die forging. The structure is altered during forging by subsequent processes of plastic deformation, recrystallization and grain growth. A numerical analysis using an rigid visco-plastic finite element model was performed to predict microstructural evolution of hot working die steel.

• 한국지반공학회논문집
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• 제18권3호
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• pp.5-12
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• 2002

투수계수는 지반공학의 문제를 해결하는 데 중요한 인자의 하나이다. 그렇지만 현장이나 실험실에서 투수계수를 구하려면 시간과 비용이 많이 든다. 이 논문에서는 입도분포를 반영하는 통계적인 계수를 이용하여 모래의 투수계수를 예측할 수 있는 식을 제안하였다. 이를 위해 36가지 입도분포의 시료를 통계적인 방법으로 조성하여 투수시험을 한 후 그 결과를 회귀분석하였다. 제안식은 변수로서 체분석시험에서 구한 모래 입경의 기하평균과 기하표준편차 또는 D_{10},D_{50},D_{60} 등과 같은 입도분포계수를 사용한다. 제안된 식의 성능을 검증하기 위해 국내 20개 지역에서 채취한 시료에 대한 투수계수의 예측치와 실측치를 비교한 결과 비교적 잘 맞는 것으로 판명되였다. 또한 제안식의 성능이 Hazen 등 다른 연구자들의 식과 비교되었다.

• 한국해안해양공학회지
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• 제18권2호
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• pp.124-136
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• 2006

백령도 용기포항 연안해역에서 2004년 6월에 채취한 총 90개 퇴적물을 분석하여 추정된 정보를 기준격자정보로 하여, 내삽기법과 퇴적물 추출 밀도변화에 따른 추정 퇴적물 입도분포 정보(중앙입경(D50) 등)의 변화를 분석하였다. 격자정보 추출방법에 의한 절대편차의 표준편차는 자료수가 많은 6월에는 $8.0 {\mu}m$ 정도, 적은 경우인 11월은 $10{\mu}m$ 이상으로 분석되었다. 표본추출밀도에 따른 격자내용과 기준격자정보를 비교하여 추정한 절대편차의 통계정보는, 표본의 수가 감소할수록 절대편차의 평균오차는 증가하는 경향을 보인다. 연구사업에서 요구되는 퇴적물 정보의 정확도(절대편차 평균기준) 수준이 10% 이하인 경우에는 50개정도의 표본이 적당한 수준으로 파악되었다. 이 경우의 표본추출밀도는 용기포항 연안해역 격자정보 전환 면적(5.9 $km^2$)을 기준으로 50개 정도를 적용하는 경우, $km^2$당 9개 정도이다.

• Structural Engineering and Mechanics
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• 제78권4호
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• pp.473-484
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• 2021

Similar to other structures, ultimate strength values showing the maximum load that the structure can resist without damaging has great importance on ships. Therefore, increasing the ultimate strength values will be an important benefit for the structure. Low carbon steels used in ships due to their low cost and good weldability. Improving the ultimate strength values without interfering with the chemical composition to prevent of the weldability properties of these steels would be very beneficial for ships. Grain refinement via severe plastic deformation (SPD) is an essential strengthening mechanism without changing the chemical composition of metallic materials. Among SPD methods, equal channel angular pressing (ECAP) is one of the most commonly used one due to its capacity for achieving bulk ultrafine-grained (UFG) materials. When the literature is examined, it is seen that there is no study about ultimate strength calculation in ships after ECAP. Therefore, the mean purpose of this study is to apply ECAP to a shipbuilding low carbon steel to be able to achieve mechanical properties and investigate the alteration of ship hull girder grillage system's ultimate strength via finite element analysis approach. A fine-grained (FG) microstructure with a mean grain size of 6 ㎛ (initial grain size was 25 ㎛) was after ECAP. This microstructural evolution brought about a considerable increase in strength values. Both yield and tensile strength values increased from 280 MPa and 425 MPa to about 420 MPa and 785 MPa, respectively. This improvement in the strength values reflected a finite element method to determine the ultimate strength of ship hull girder grillage system. As a result of calculations, it was reached significantly higher ultimate strength values (237,876 MPa) compared the non-processed situation (192,986 MPa) on ship hull girder grillage system.

• 한국지형학회지
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• 제25권1호
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• pp.1-17
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• 2018

The characteristics and burial ages of sand sediments on the Jiduri coast in Daechung-myeon, Ongjin-gun, Incheon were investigated. Daecheong Island is the area where the characteristics of the rocky coast and sand coast are shown. Various studies have been conducted on the Okjukdong sand dune that appears in the north of the island. However, there has been no study on the sandy sedimentary topography of the Jiduri and Moraewul area in the south. The sandy sedimentary terrain of Jiduri is divided into sandy beaches, sand dunes and sand deposits along the slope including climbing dune. Overall, the depth of sandy sediments in Jiduri is not deep. The characteristics of sandy sediments and burial ages were investigated at an elevation of about 23 m above sea level at the back of Jiduli Beach and 46 m above sea level at the ridge line between Jiduri and Moraewol. From the Jiduri coast to the hillside behind, the average grain size decreases and the sorting becomes better as it moves from the intertidal zone to the beach and the foredune. This indicates the selective sand transport by the wind and can be judged by the terrain formed under the current sedimentation environment. The average grain size at the upper part of the section of JD-1 (elevation of about 23m MSL) was $1.6918{\varphi}$ of medium sand. The sorting was $0.4584{\varphi}$, skewness was -1.0491 and kurtosis was -1.2411, respectively. Particularly, the average particle size of the crosssection issomewhat uniform, but the color of the constituent material changes from brown to black. In the case of JD-2 (about 46 m MSL), the mean grain size of the section was $1.7943{\varphi}$, the sorting was 0.4931, the skewness was -1.1163, and the kurtosis was 1.2133. On the other hand, the brown and black layers of JD-1 exhibited a burial age of $0.1{\pm}0.0ka$ and the JD-2 had a burial age of $0.7{\pm}0.0ka$.