• Advances in concrete construction
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• 제9권3호
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• pp.313-326
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• 2020

Glass fiber-reinforced polymer (GFRP) bars have been introduced as an effective alternative for the conventional steel reinforcement in concrete structures to mitigate the costly consequences of steel corrosion. However, despite the superior performance of these composite materials in terms of corrosion, the effect of replacing steel reinforcement with GFRP on the seismic performance of concrete structures is not fully covered yet. To address some of the key parameters in the seismic behavior of GFRP-reinforced concrete (RC) structures, two full-scale beam-column joints reinforced with GFRP bars and stirrups were constructed and tested under two phases of loading, each simulating a severe ground motion. The objective was to investigate the effect of damage due to earthquakes on the service and ultimate behavior of GFRP-RC moment-resisting frames. The main parameters under investigation were geometrical configuration (interior or exterior beam-column joint) and joint shear stress. The performance of the specimens was measured in terms of lateral load-drift response, energy dissipation, mode of failure and stress distribution. Moreover, the effect of concrete damage due to earthquake loading on the performance of beam-column joints under service loading was investigated and a modified damage index was proposed to quantify the magnitude of damage in GFRP-RC beam-column joints under dynamic loading. Test results indicated that the geometrical configuration significantly affects the level of concrete damage and energy dissipation. Moreover, the level of residual damage in GFRP-RC beam-column joints after undergoing lateral displacements was related to reinforcement ratio of the main beams.

• Journal of Mechanical Science and Technology
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• 제19권2호
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• pp.634-648
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• 2005

Performed here is a comparative assessment study for the probabilistic fracture mechanics approach of the pressurized thermal shock of the reactor pressure vessel. A round robin consisting of one prerequisite deterministic study and five cases for probabilistic approaches is proposed, and all organizations interested are invited. The problems are solved by the participants and their results are compared to issue some recommendation of best practices and to assure an understanding of the key parameters in this type of approach, like transient description and frequency, material properties, defect type and distribution, fracture mechanics methodology etc., which will be useful in the justification through a probabilistic approach for the case of a plant over-passing the screening criteria. Six participants from 3 organizations responded to the problem and their results are compiled and analyzed in this study.

• 대한조선학회논문집
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• 제34권1호
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• pp.68-76
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• 1997

본 논문에서는 선박 및 해양 구조물을 구성하는 용접 판구조물의 변형 및 잔류응력 등 용접 초기 결함을 효율적으로 평가할 수 있는 열탄소성 해석방법을 정립하였다. 또한 평판의 선상가열공법(line heating process)을 열탄소성 시뮬레이션함으로써 작업의 고능률화 및 자동화를 위한 기초연구를 수행하였다. 판구조물에 대한 열전도 해석을 수행하기 위하여 해석적인 방법과 수치적인 방법을 병행하였다. 판구조물의 열탄소성 해석방법에 있어서는 초기변형도법에 근거한 유한요소법을 사용하였으며, 증분 구간중 소성 구역에서는 응력 증분 및 항복응력 중분의 2 차항까지 고려해서 시간 증분을 최적 제어함으로써 해석 불능에 빠지는 문제를 극복하였다. 특히 응력 중분에 탄성계수의 온도에 따른 증분을 2 차항까지 포함시켰다. 평판의 두께와 입열량을 변화시키면서 일련의 용접 열탄소성 실험을 수행하였는 바, 온도 및 용접 변형을 계측하여 수치 계산 결과와 비교하여 상호 부합성이 양호함을 확인하였다.

• Biotechnology and Bioprocess Engineering:BBE
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• 제8권4호
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• pp.246-251
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• 2003

The blood-brain barrier (BBB) is composed of the brain capillaries, which are lined by endothelial cells displaying extremely tight intercellular junctions. Several attempts at creating an in vitro model of the BBB have been met with moderate success as brain capillary endothelial cells lose their barrier properties when isolated in cell culture. This may be due to a lack of recreation of the in vivo endothelial cellular environment in these models, including nearly constant contact with astrocyte foot processes. This work is motivated by the hypothesis that growing endothelial cells on one side of an ultra-thin, highly porous membrane and differentiating astrocyte or astrogliomal cells on the opposite side will lead to a higher degree of interaction between the two cell types and therefore to an improved model. Here we describe our initial efforts towards testing this hypothesis including a procedure for membrane fabrication and methods for culturing endothelial cells on these membranes. We have fabricated a 1 $\mu\textrm{m}$ thick, 2.0 $\mu\textrm{m}$ pore size, and 55% porous membrane with a very narrow pore size distribution from low-stress silicon nitride (SiN) utilizing techniques from the microelectronics industry. We have developed a base, acid, autoclave routine that prepares the membranes for cell culture both by cleaning residual fabrication chemicals from the surface and by increasing the hydrophilicity of the membranes (confirmed by contact angle measurements). Gelatin, fibronectin, and a 50/50 mixture of the two proteins were evaluated as potential basement membrane protein treatments prior to membrane cell seeding. All three treatments support adequate attachment and growth on the membranes compared to the control.

• 대한토목학회논문집
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• 제36권6호
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• pp.999-1010
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• 2016

최근 국내에서는 고강도 강연선이 실구조물에 적용되는 사례가 늘어나고 있다. 이 연구에서는 LNG 저장탱크에 통상적으로 적용되는 1,860 MPa급 강연선을 2,400 MPa급 고강도 강연선으로 대체할 때 쉬스 배치 간격 증가에 따른 구조적인 영향을 고찰해 보았다. 먼저, LNG 탱크의 원통형 벽체를 모사하는 유한요소모델에 원환텐던 및 수직텐던의 프리스트레싱 효과를 등가하중으로 가하되 프리스트레싱 효과의 총합은 일정한 상태에서 텐던의 간격 및 긴장력을 조절한 결과, 고강도 강연선을 적용해도 설계 시 요구되는 소정의 응력 분포를 구현할 수 있는 것으로 나타났다. 또한, LNG 탱크 벽체 일부분을 모사하는 실대형 실험체를 제작하고 15.2 mm 직경 고강도 강연선이 31개 삽입된 쉬스를 2개 배치하여 매우 높은 수준의 프리스트레싱 힘이 콘크리트에 적절히 전달되는지 관찰하였다. 한편, 세계 최대 용량인 270,000 kl급 LNG 탱크의 유한요소모델을 구축하고 고강도 강연선을 적용했을 때의 프리스트레싱 효과를 일반 강연선의 경우와 비교하였으며, LNG 누출 사고 시에도 여유압축응력 및 여유압축구간과 같은 수밀성 규정을 만족함을 확인하였다. 이 연구결과는 2,400 MPa급 고강도 강연선이 실제 LNG 탱크에 적용될 때 유용하게 활용될 것으로 기대된다.

• 한국환경과학회지
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• 제20권9호
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• pp.1141-1149
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• 2011

The three-dimensional hydrodynamic model was simulated to understand coastal sea front of formation and seasonal variation in the Southern Sea of Korea. In this study, we used to concept of stratification factor, to realize seasonal distribution of stratification coefficient which of seasonal residual flow, considered with, tide, wind and density effect. Tidal current tends to flow westward during the flood and eastward during ebb. The current by the wind stress showed to be much stronger the coastal than the offshore area in the surface layer. And the current by the horizontal gradient of water density showed to be relatively weak in the coastal area, with little seasonal differences. On the other hand, the flow in the offshore area showed results similar to that of the Tsushima Warm Current. The stratification factor (SHv) was calculated by taking into account the total flow of tide, wind and density effect. In summer, the calculated SHv distribution ranged from 2.0 to 2.5, similar to that of the coastal sea front. The horizontal temperature gradient showed to be strong during the winter, when the vertical stratification is weak. On the other hand, the horizontal gradient became weak in summer, during which vertical stratification is strong. Therefore, it is presume that the strength of vertical stratification and the horizontal temperature gradient affect the position of the coastal sea front.

• 한국지반신소재학회논문집
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• 제16권1호
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• pp.73-83
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• 2017

모래 및 실트 함유량이 우세한 서해안 저소성 지반(인천, 화성, 군산)에서 실시된 실내 및 현장시험으로부터 얻어진 비배수전단 강도를 이용하여 피에조콘계수(Nkt)를 분석한 후, 이에 대한 적용성을 평가하였다. 인천, 화성 및 군산지역에서 얻어진 일축압축 강도에 의한 콘계수(Nkt)는 19~23, 간이 CU 강도에 의한 값은 13~13.8, 현장베인강도에 의한 값은 11.6~13.1로 평가되었다. 이는 저소성 실트 지반조건에서 일축압축강도가 과소평가되는 원인에 의한 것으로 간이 CU 강도 적용조건과 비교했을 때 콘계수(Nkt)가 약 1.8배 전후로 커지며 분산되는 경향을 나타냈다. 저소성 실트 지반에서 수행된 CPTU 데이터를 이용하여 콘계수(Nkt)를 평가할 때에는 지반의 입도분포, 액소성한계 등의 물리적 특성, 지층 내의 sandseam 분포 등으로 인한 콘선단저항(qt) 및 주면마찰력(fs)의 불규칙한 분포, 간극수압계수(Bq)를 종합적으로 분석하여 수행하는 것이 바람직할 것으로 판단된다.

• Design & Manufacturing
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• 제10권1호
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• pp.19-25
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• 2016

Connectors are very important components that transmit electric signals to different parts. It must maintain intensity of the connector to prevent defects from impact and maintain contact to transmit electric signals. Most of the external parts of the connector, which act as the main framework, are formed by injection molding. However, bend deformation occurs for injection molded products due to the residual stress left inside the product after product molding. When the bend deformation is large, it does not come into complete contact when being assembled with other parts, which leads to connector contact intensity not being properly maintained. In result, the main role of the connector, which is to transmit electric signals, cannot be performed. In order to address this problem, this study conducted bend deformation cause analysis through bend deformation analysis to predict and prevent bend deformation of housings and wafers, which are injection molded products of pressure welded connectors that are normally applied in compact mobile and display products. Bend deformation analysis was carried out by checking the charging time, pressure distribution and temperature distribution through wire to board connector wafer and housing injection molding analysis. Based on the results of the bend deformation analysis results, the cause of the bend deformation was analyzed through deformation resulting from disproportional cooling, deformation resulting from disproportional contraction, and deformation resulting from ingredient orientation. In result, it was judged that the effects for bend deformation were biggest due to disproportional contraction for both the pressure welded connector wafer and housing.

• Composites Research
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• 제35권3호
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• pp.188-195
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• 2022

본 논문은 멀티스케일 공정-구조 해석의 방법론을 제안하고 단섬유층과 직물층으로 이루어진 배터리 하우징 파트에 적용한다. 특별히 마이크로스케일 대표체적요소(RVE: Representative Volume Element)안 기지의 불확정성을 고려하였다. 마이크로스케일의 RVE내 기지 물성의 랜덤한 공간내 분포는 KLE(Karhunen-Loeve Expansion)을 통해 구현하였다. 공간상 랜덤분포된 기지 물성을 갖는 RVE의 유효 물성을 전산균질화를 통해 얻어 매크로스케일 유한요소 모델에 매핑하였다. 또한 하이브리드 공정해석을 통해 압축 성형 해석으로부터 얻은 잔류응력과 섬유배향을 매핑한 유한요소 모델과 드레이핑 공정 해석결과로부터 얻어진 섬유배향을 매핑한 모델을 결합하였다. 본 연구에 제안된 방법은 배터리 하우징 뿐만 아니라 다양한 재료 구성을 갖는 복합재료의 공정-구조해석을 통해 설계요구도를 엄밀하게 평가할 수 있을 것이라 기대된다.

• 대한치과보철학회지
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• 제42권4호
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• pp.397-411
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• 2004

Purpose: The purpose of this study was to determine the effect of anchorage systems and palatal coverage of denture base on load transfer in maxillary implant-supported overdenture. Material and methods: Maxillary implant -supported overdentures in which 4 implants were placed in the anterior region of edentulous maxilla were fabricated, and stress distribution patterns in implant supporting bone in the case of unilateral vertical loading on maxillary right first molar were compared with each other depending on various types of anchorage system and palatal coverage extent of denture base using three-dimensional photoelastic stress analysis. Two photoelastic overdenture models were fabricated in each anchorage system to compare with the palatal coverage extent of denture base, as a result we got eight models : Hader bar using clips(type 1), cantilevered Hader bar using clips(type 2), Hader bar using clip and ERA attachments(type 3), cantilevered milled-bar using swivel-latchs and frictional pins(type 4). Result: 1. In all experimental models, the highest stress was concentrated on the most distal implant supporting bone on loaded side. 2. In every experimental models with or without palatal coverage of denture base, maximum fringe orders on the distal ipsilateral implant supporting bone in an ascending order is as follows; type 3, type 1, type 4, and type 2. 3. Each implants showed compressive stresses in all experimental models with palatal coverage of denture base, but in the case of those without palatal coverage of denture base, tensile stresses were observed in the distal contralateral implant supporting bone. 4. In all anchorage system without palatal coverage of denture base, higher stresses were concentrated on the most distal implant supporting bone on loaded side. 5. The type of anchorage system affected in load transfer more than palatal coverage extent of the denture base. Conclusion: To the results mentioned above, in the case of patients with unfavorable biomechanical conditions such as not sufficient number of supporting implants, short length of the implant, and poor bone quality, selecting a resilient type attachment or minimizing the distal cantilevered bar is considered to be an appropriate method to prevent overloading on implants by reducing cantilever effect and gaining more support from the distal residual ridge.