• 한국구조물진단유지관리공학회 논문집
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• 제12권3호
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• pp.93-100
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• 2008

혹독한 자연환경하에서의 구조물의 내구성이 주요한 관심사도 대두되면서 건설분야에서 섬유강화폴리머의 사용이 점차 증가하고 있는 추세이다. 본 연구에서는 FRP bar를 휨부재의 휨보강근으로서의 적용가능성을 평가하기 위하여 휨실험을 수행하였다. 탄소섬유, 유리섬유 및 탄소와 유리섬유를 혼합한 hybrid 섬유 보강근을 사용하여 보강량을 변화시킨 12개의 실험체를 제작하여 실험을 수행하였으며, 그결과는 파괴형태, 모멘트-변위, 휨강도, 연성지수 및 단면에서의 변형율분포 등에 대하여 분석하였다. 실험결과는 ACI 기준에 제시된 모델과 비교하였으며, 전체적으로 보의 휨강도는 강도설계이론에 의한 결과와 거의 유사한 것으로 나타났다. 그러나 처짐의 경우에는 유리섬유의 경우는 이론이 과대평가 되었으며, 탄소섬유는 과소평가되는 것으로 나타났다.

• Journal of the Korean Wood Science and Technology
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• 제39권6호
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• pp.538-547
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• 2011

이 연구에서는 녹차와 목재섬유를 복합한 친환경 복합보드를 건축내장재로 활용하기 위하여, 목재섬유에 대한 녹차의 배합비율을 달리한 녹차-목재섬유 복합보드를 제작하였고, 복합보드의 동적탄성률에 미치는 녹차의 배합비율 및 바인더로 사용한 접착제의 영향을 조사하였다. 녹차-목재섬유복합보드의 동적탄성률은 녹차를 넣지 않은 대조보드(control boards)의 그것보다 적었고, 녹차배합비율이 증가할수록 커지는 경향을 나타내었다. 또한, 보드제조에 사용된 바인더의 종류에 따라 동적탄성률의 차이가 나타났는데, $E_1$급의 요소수지가 $E_0$급의 요소수지보다 1.06~1.54배의 높은 값을 나타내었으며, 녹차의 배합비율이 커질수록 양자의 차이는 커지는 것이 확인되었다. 한편, 녹차-목재섬유복합보드의 동적탄성률과 휨 강도성능과는 비교적 높은 상관관계가 확인되어 일부 편차가 큰 조건을 제외하고 동적탄성률로부터 정적 휨 강도성능의 예측이 가능할 것으로 확인되었다.

• Composites Research
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• 제30권2호
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• pp.158-164
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• 2017

섬유금속적층판은 금속 판재와 섬유 강화 플라스틱을 적층한 하이브리드 소재 중 하나다. 섬유금속적층판은 부품 경량화 측면을 고려했을 시, 뛰어난 충격흡수능력을 가지고 있기 때문에 자동차 및 항공우주 산업에서 적용 및 연구를 진행하고 있는 추세다. 특히, 자동차의 측면 도어 임펙트 빔의 경우, 기존의 금속소재에서 복합재료로 대체하기 위한 연구가 활발히 진행 중이다. 본 연구에서는 자동차의 측면 도어 임펙트 빔을 금속소재와 자기 강화형 폴리프로필렌을 적층한 섬유금속적층판으로 대체하는 것이 목표다. 3가지 종류의 임펙트 빔의 3점 굽힘 시험 수치해석을 통해 단면적 대비 굽힘 저항력의 크기를 비교하였다. 그 후, 제작 실현성을 고려하여 굽힘 저항력이 우수한 이중모자형 임펙트 빔을 순수 DP 980과 섬유금속적층판으로 제작하여 자동차 측면 도어에 설치된 모델을 상정하고 충돌 해석을 수행하였다. 결과적으로 섬유금속적층판을 사용한 임펙트 빔은 기존의 DP 980보다 무게 대비 충격 에너지 흡수 능력이 약 7배 높음을 알 수 있었다.

• Journal of the Optical Society of Korea
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• 제20권4호
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• pp.488-499
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• 2016

We present a design and optical simulation of a cost-effective hybrid daylighting/LED system composed of mixing sunlight and light-emitting diode (LED) illumination powered by renewable solar energy for indoor lighting. In this approach, the sunlight collected by the concentrator is split into visible and non-visible rays by a beam splitter. The proposed sunlight collector consists of a Fresnel lens array. The non-visible rays are absorbed by the solar photovoltaic devices to provide electrical power for the LEDs. The visible rays passing through the beam splitters are coupled to a stepped thickness waveguide (STW) by tilted mirrors and confined by total internal reflection (TIR). LEDs are integrated at the end of the STW to improve the lighting quality. LEDs’ light and sunlight are mixed in the waveguide and they are coupled into an optical fiber bundle for indoor illumination. An optical sensor and lighting control system are used to control the LED light flow to ensure that the total output flux for indoor lighting is a fixed value when the sunlight is inadequate. The daylighting capacity was modeled and simulated with a commercial ray tracing software (Lighttools^TM). Results show that the system can achieve 63.8% optical efficiency at geometrical concentration ratio of 630. A required accuracy of sun tracking system achieved more than ±0.5^o . Therefore, our results provide an important breakthrough for the commercialization of large scale optical fiber daylighting systems that are faced with challenges related to high costs.

• 상하수도학회지
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• 제32권4호
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• pp.357-361
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• 2018

Forward osmosis (FO) process has been attracting attention for its potential applications such as industrial wastewater treatment, wastewater reclamation and seawater desalination. Particularly, in terms of fouling reversibility and operating energy consumption, the FO process is assumed to be preferable to the reverse osmosis (RO) process. Despite these advantages, there is a difficulty in the empirical step due to the lack of separation and recovery techniques of the draw solution. Therefore, rather than using FO alone, recent developments of the FO process have adapted a hybrid system without draw solution separation/recovery systems, such as the FO-RO osmotic dilution system. In this study, we investigated the performance of the hollow fiber FO module according to various operating conditions. The change of permeate flow rate according to the flow rates of the draw and feed solutions in the process operation is a factor that increases the permeate flow rate, one of the performance factors in the positive osmosis process. Our results reveal that flow rates of draw and feed solutions affect the membrane performance, such as the water flux and the reverse solute flux. Moreover, use of hydraulic pressure on the feed side was shown to yield slightly higher flux than the case without applied pressure. Thus, optimizing the operating conditions is important in the hollow fiber FO system.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.967-972
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• 2004

The role of transfer films formed during sliding of polymer composites against steel counterfaces was studied in terms of the tribological behaviors of composites. Four kinds of composites were included in this study: (1) unfilled PPS, (2) PPS+2%CuO, (3) PPS+2%CuO+5% carbon fiber (CF), and (4) PPS+2%CuO+15%Kevlar. The filler material CuO was in nanoscale particulate form and the reinforcing material was in the form of short fibers. The composites were prepared by compression molding at $310^{\circ}C$ and sliding tests were run in the pin-on-disk sliding configuration. The counterface was made of tool steel hardened to 55-60 HRC and finished to a surface roughness of 0.09-0.10 ${\mu}m$ Ra. Wear tests were run for 6 hrs at the sliding speed of 1 m/s and contact pressure of 0.65 MPa. Transfer films formed on the counterfaces during sliding were investigated using AFM and SEM. The results showed that as the transfer film became smooth and uniform, wear rate decreased. PPS+2%CuO+15%Kevlar composite showed the lowest steady state wear rate in this study and its transfer film showed the smoothest and the most uniform characteristics. The examination of worn surfaces of PPS+2%CuO composite using X-ray area scanning (dot mapping) showed back-transfer of steel counterface material to the polymer pin surface. This behavior is believed to strengthen the polymer pin surface during sliding thereby contributing to the decrease in wear rate.

• 한국강구조학회 논문집
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• 제16권5호통권72호
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• pp.609-619
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• 2004

유럽을 중심으로 스틸스터드의 약점으로 지목 받고 있는 열교현상을 억제하기 위한 스터드 개선 연구가 활발히 진행되고 있다. 이 연구는 크게 마감재와 접촉 면적을 줄이는 방법, 웨브면에서 열전달 경로를 늘이는 방법, 열전도성이 낮은 소재를 사용하는 방법, 그리고 스터드를 피복하는 방법으로 구분할 수 있다. 비교적 저층의 주거용 건축물을 대상으로 하는 국외의 경우 에너지 소비에 초점이 맞춰져 있지만, 본 연구의 경우 중층화를 대비하여 구조적 성능도 고려하여 아연도금강판(SGC58)과 FRP를 에폭시로 부착하여 150SL 형태의 복합스터드를 개발하였다. 복합스터드의 소재로는 두께 1.0mm과 1.2mm 강판과 두께 4mm(4ply), 6mm(6ply)의 FRP를 적용하였고, 4가지의 접합 상세에 대한 제작 및 실험을 통해 최종적으로 우수한 결과를 보인 2가지를 선택하였다. 이와 같은 과정을 거쳐 개발된 복합스터드의 압축 성능을 확인하기 위해 2가지 접합 상세에 대해 단면 높이인 150mm에 대해 3, 6, 9, 12배 길이에 대해 압축 실험을 계획하였고, 기존 스틸 스터드와 비교하기 위하여 동일 형태의 비교 실험체도 제작하였다. 실험결과, 복합스터드의 최대하중은 강판 두께 1.0mm인 경우 동일 두께의 스틸 스터드보다 평균 1.62배, 1.2mm인 경우 평균 1.46배 증가하였으며, 가력 종료 시점에 이르기까지 일체 거동을 보여 구조적으로 우수함이 입증되었다.

• Advances in aircraft and spacecraft science
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• 제4권6호
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• pp.679-699
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• 2017

The aim of this study is to perform a finite element analysis of the Von Mises stresses distribution in the adhesive layer and of the J-Integral for a damaged plate repaired by a composite patch. Firstly, we study the effect of the fiber orientation, especially the position of the layers that have orientation angle different of $0^{\circ}$ from the first layer which is in all cases of our study oriented at ($0^{\circ}$) on the J-Integral. Secondly, we evaluate the effects of the mechanical properties of the patch and the use of a hybrid patch on the reduction of stresses distribution and J-Integral. The results show clearly that the stacking sequence for the composite patch must be selected to absorb optimally the stresses from the damaged area and to position the various layers of the composite under the first layer whose fibers orientation will remain in all cases equal to $0^{\circ}$. The use of a hybrid composite reduces significantly the J-Integral and the stresses in both damaged plate and the adhesive layer.

• Computers and Concrete
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• 제21권2호
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• pp.167-179
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• 2018

Reactive powder concrete (RPC) is a type of ultra-high strength cement-based material with a dense microstructure, which is made of ultra-fine powders. RPC demonstrate a very brittle behavior, thus adding fibers improves its mechanical properties. In this study, it was attempted to investigate the effect of using steel and polyvinyl alcohol (PVA) fibers as well as their combination on the properties of RPC. In this regard, hooked-end crimped steel fibers together with short PVA fibers were utilized. Steel and PVA fibers were used with the maximum volume fraction of 3% and 0.75%, respectively, and also different combinations of these fibers were used with the maximum volume fraction of 1% in the concrete mixes. In total, 107 concrete specimens were prepared, and the effect of fiber type and volume fraction on the physico-mechanical properties of RPC including compressive strength, tensile strength, modulus of elasticity, density, and failure mode was explored. In addition, the effect of the curing type on the properties of compressive strength, modulus of elasticity, and density of RPC was evaluated. Finally, coefficients for conversion of cubic compressive strength to cylindrical one for the RPC specimens were obtained under the two curing regimes of heat treatment and standard water curing.

• 한국자동차공학회논문집
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• 제15권6호
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• pp.50-61
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• 2007

The structural stiffness, strength and stability on the bodyshell and floor structures of the Korean Low Floor Bus composed of laminate, sandwich panels and metal reinforced frame were evaluated. The laminate composite panel and facesheet of sandwich panel were made of WR580/NF4000 glass fabric/epoxy laminate, while aluminum honeycomb or balsa was applied to the core materials of the sandwich panel. A finite element analysis was used to verify the basic design requirements of the bodyshell and the floor structure. The use of aluminum reinforced frame and honeycomb core was beneficial for weight saving and structural performance. The symmetry of the outer and inner facesheet thickness of sandwich panels did not affect the structural integrity. The structural strength of the panels was evaluated using Von-Mises criterion for metal structures and total laminate approach criterion for composite structures. All stress component of the bodyshell and floor structures were safely located below the failure stresses. The total laminate approach is recommended to predict the failure of hybrid sandwich composite structures at the stage of the basic design.