• Structural Engineering and Mechanics
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• 제65권6호
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• pp.679-687
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• 2018

In composite materials technology, the fiber-reinforced polymers (FRP) have opened up new horizons in infrastructural engineering field for strengthening existing structures and components of structure. The Carbon fiber reinforced polymer (CFRP) sheets are well suited for RC columns to this application because of their high strength to weight ratio, good fatigue properties and excellent resistance to corrosion. The main focus of present experimental work is to investigate effect of shapes on axial behavior of CFRP wrapped RC columns having same cross-sectional area and slenderness ratio. The CFRP volumetric ratio and percentage of steel are also adopted constant for all the test specimens. A total of 18 RC columns with slenderness ratio four were cast. Nine columns were control and the rest of nine columns were strengthened with one layer of CFRP wrap having 35 mm of corner radius. Columns confined with CFRP wrap were designed using IS: 456:2000 and ACI 440.2R.08 provisions. All the test specimens were loaded for axial compression up to failure and failure pattern for each shaped column was investigated. All the experimental results were compared with analytical values calculated as per the ACI-440.2R-08 code. The test results clearly demonstrated that the axial behavior of CFRP confined RC columns is affected with the change in shapes. The axial deformation is higher in CFRP wrapped RC circular column as compared to square and rectangular columns. Stress-strain behaviour revealed that the yield strength gained from CFRP confinement was significant for circular columns as compare to square and rectangular columns. This behaviour may be credited due to effect of shape on lateral deformation in case of CFRP wrapped circular columns at effective confinement action.

• Steel and Composite Structures
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• 제30권5호
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• pp.417-432
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• 2019

This paper presents the results of axial compression testing and numerical modeling on reinforced concrete columns (RCC) with normal concrete (NC) and high-strength concrete (HSC), RCC confined by glass-fiber reinforced plastic pipes (GRP) casing as well as carbon fiber reinforced polymer (CFRP), The major parameters evaluated in the experiments were the effects of concrete type, GRP casing and CFRP wrapping, as well as the number of CFRP layers. 12 cylindrical RCC ($150{\times}600mm$) were prepared and divided into two groups, NC and HSC. Each group was divided into two parts; with and without GRP casing. In each part, one column was without CFRP strengthening layer, a column was wrapped with one CFRP layer and another column with two CFRP layers. All columns were tested under concentrated compression load. Numerical modeling was performed using ABAQUS software and the results of which were compared with experimental findings. A good agreement was found between the results. Results indicated that the utilization of CFRP wrapping and GRP casing improved compression capacity and ductility of RCC. The addition of one and two layer-FRP wrapping increased capacity in the NC group to an average of 18.5% and 26.5% and in the HSC group to an average of 10.2% and 24.8%. Meanwhile, the utilization of GRP casing increased the capacity of the columns by 3 times in the NC group and 2.38 times in the HSC group. The results indicated that although both CFRP wrapping and GRP casing increased confinement, the GRP casing gave more increase capacity and ductility of the RCC due to higher confinement. Furthermore, the confinement effect was higher on NC group.

• Smart Structures and Systems
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• 제23권5호
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• pp.495-506
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• 2019

This paper presents the results of axial pressure testing on reinforced concrete columns (RCCs) filled with confined normal concrete (NC) and high-strength concrete (HSC) using glass-fiber reinforced plastic pipes (GRP) casing as well as fiber reinforced polymer (FRP). This study aims to evaluate the behavior and mechanical properties of columns confined with GRP casing and FRP wrapping under pressure loads. The major parameters in the experiments were the type of concrete, the effect of GRP casing and FRP wrapping, as well as the number of FRP layers. 12 cylindrical RCCs (150*600) mm were prepared and divided into two groups, NC and HSC, and each group was divided into two parts. In each part, one column was without FRP strengthening layer, a column was wrapped with one FRP layer and another column with two FRP layers. All columns were tested under concentrated compression load. The results of the study showed that the utilization of FRP wrapping and GRP casing improved compression capacity and ductility of RCCs. The addition of one and two layers-FRP wrapping increased compression capacity in the NC group to an average of 18.5% and 26.5% and to an average of 10.2% and 24.8% in the HSC group. Meanwhile, the utilization of GRP casing increased the compression capacity of the columns by 4 times in the NC group and 3.38 times in the HSC group. The results indicated that although both FRP wrapping and GRP casing result in confinement, the GRP casing resulted in increased compression capacity and ductility of the RCCs due to higher confinement. Furthermore, the confinement effect was higher on columns made with NC.

• Elastomers and Composites
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• 제35권1호
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• pp.29-37
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• 2000

본 연구에서는 elastomer의 기초 연구로써 두개의 침투할 수 없는 평판사이로 국한시킨 용융상태에서 두개의 다른 사슬 길이를 가진 고분자의 거동에 대한 결과를 보여 주었다. 입방 격자시뮬레이션은 reptation과 crankshaft bond flip 이동의 조합에 따른 방법으로 유도되었다. 10개의 구슬로 엮어진 544개의 짧은 사슬과 160개의 구슬로 엮어진 136개의 긴 사슬로 구성된 전체 680개의 사슬은 20개의 격자 충에 투입되었다. 공유결합으로 연결된 구슬사이의 energetic 상호인력은 없고 반면에 모든 다른 이웃들은 truncated 6-12 Lennard-Jones 포텐셜로서 상호작용하고 있다고 가정하였다. 수치모사 결과의 분석으로부터 순수한 entropic 효과로 인하여 짧은 사슬이 우선적으로 표면에 도달하는 것을 보여 주었다 또한 짧은 사슬의 질량밀도중심은 표면근처에서 최고값을 보여주었다. 이것은 긴 사슬의 경우와 상반되는 현상이다. 그러나 짧은 사슬과 긴 사슬의 segment는 결합 정렬에 있어서는 큰 변화를 주지 않았다.

• 접착 및 계면
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• 제14권2호
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• pp.82-87
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• 2013

본 연구에서는 레졸, 질산철 그리고 트리블럭 공중합체를 이용하여 직접 탄화과정에 의해 자성체 나노입자가 분산된 탄소나노세공체를 합성하였다. 나노세공 마그네타이트/카본($Fe_3O_4$/carbon) 나노복합체는 낮은 마그네타이트 함량(1 wt%)을 가지고 잘 배열된 이차원적 육방체 구조(p6mm)를 보이며, 균일한 세공크기(3.6 nm), 높은 표면적(635 $m^2/g$)과 세공부피(0.48 $cm^3/g$)를 가진다. 작은 입자크기(10.2 nm)를 가지는 마그네타이트 나노입자는 초상자기성(7.7 emu/g)을 보이고 탄소 세공벽 내에 잘 분산되었다. 나노세공 마그네타이트/카본 물질은 최대 995 mg/g의 아이부프로펜 흡착량을 보였다. 또한, 자석을 이용하여 용액과 나노세공 마그네타이트/카본 물질의 분리가 용이하였다. 본 연구에서 제조된 나노복합체는 우수한 아이부프로펜 흡착제로 작용하였다.

• 폴리머
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• 제37권1호
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• pp.52-60
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• 2013

셀룰로오스 아세테이트(CA) 섬유를 $Na_2CO_3$ 용액으로 가수분해하여 탈아세테이트 반응시키면 레이온 섬유로 전환된다. 이때 처리조건을 조절함으로써 표면만 가수분해시켜, 표면은 레이온 성분이고 내부는 CA 성분으로 된 sheath-core형 표면가수분해 CA(SH-CA) 섬유를 얻었다. 시료들의 가수분해는 FTIR 스펙트럼 및 WAXD 패턴으로 분석하였으며, CA 성분을 아세톤으로 용출시킨 시료들의 SEM 사진으로부터 sheath-core 구조를 확인하였다. 이 sheath-core 형태의 SH-CA 섬유로 된 벨벳 직물을 사용하여, 액정디스플레이(LCD)용 폴리이미드 배향막을 러빙시키고 편광 FTIR 스펙트럼으로 분석하여 이 SH-CA 섬유 벨벳직물이 LCD용 러빙포로 사용될 수 있음을 확인하였다.

• Fibers and Polymers
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• 제2권3호
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• pp.135-140
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• 2001

Organic-inorganic hybrid composites consisting of poly(vinylidene fluoride) (PVDF) and SiO$_2$ were prepared through a sol-gel process and the crystallization behavior of PVDF in the presence of $SiO_2$ networks was investigated by spectroscopic, thermal and x-ray diffraction measurements. The hybrid composites obtained were relatively transparent, and brittleness increased with increasing content of tetraethoxysilane (TEOS). It was regarded from FT-lR and DSC thermal analyses that at least a certain interaction existed between PVDF molecules and the $SiO_2$ networks. X-ray diffraction measurements showed that all of the hybrid samples had a crystal structure of PVDF ${\gamma}$-phase. Fresh gel prepared from the sol-gel reaction showed a very weak x-ray diffraction peak near 2$\theta$=$21^{\circ}$ due to PVDF crystallization, and Intensity increased grade-ally with time after gelation. The crystallization behavior of PVDF was strongly affected by the amount of $SiO_2$ networks. That is, $SiO_2$ content directly influenced preference and disturbance fur crystallization. In polymer-rich hybrids, $SiO_2$ networks had a favorable effect on the extent of PVDF crystallization. In particular, the maximum portent crystallinity of PVDF occurred at the content of 3.7 wt% $SiO_2$ and was higher than that of pure PVDF. However. beyond about 10 wt% $SiO_2$, the crystallization of PVDF was strongly confined.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 C
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• pp.1196-1198
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• 1995

In this paper, stability improvement of fragile LB films was attempted by monolayers at the air-water interface and crosslinking of the resulting LB films. The spreading polymers were synthesized by radical copolymerization of monoalkyl with oligoethyleneglycol methyl ether, and poly(allylamine) was employed as the subphase polymer. The monolayer properties have been studied by the surface pressure-area($\pi$-A) isotherms. Interaction between polymers and metal ions at the air-water interface and in their LB films were investigated. From the FT-IR(Reflection and Transmission) spectra, the formation of carboxylate ions and the relative orientation of the side chains could be confined. The monolayers were transferable on various substrates, and the resulting LB films were characterized by SEM and VIS-UV absorbance.

• International Journal of Precision Engineering and Manufacturing
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• 제8권4호
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• pp.63-69
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• 2007

The two-photon stereolithography (TPS) process is a promising technique for the fabrication of real three-dimensional (3D) nano/micro-structures via application of a femto-second laser, In TPS, when a near-infrared ultrashort-pulsed laser is closely focused onto a confined volume of photocurable resin, only the local area at the center of the focus is cured. Therefore, real 3D microstructures with resolution under the diffraction limit can be fabricated through a layer-by-layer accumulative technique, This process provides opportunities to develop neo-conceptive nano/micro devices in IT/BT industries, However, a number of issues, including development of effective fabrication methods, highly sensitive and functional materials, and neo-conceptive devices using TPS, must be addressed for the realization of industrial application of TPS. In this review article, we discuss our efforts related to TPS: effective fabrication methods, diverse two-photon curable materials for high functional devices, and applications.

• Structural Engineering and Mechanics
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• 제48권5호
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• pp.737-755
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• 2013

This paper aims to develop a practical approach to modeling of fiber reinforced polymers (FRP) strengthened masonry panels. The main objective is to provide suitable relations for the material characterization of the masonry constituents so that the finite element applications of elasto-plastic theory achieves a close fit to the experimental load-displacement diagrams of the walls subjected to in-plane shear and compression. Two relations proposed for masonry columns confined with FRP are adjusted for the cohesion and the internal friction angle of both units and mortar. Relating the mechanical parameters to the uniaxial compression strength and the hydrostatic pressure acting over the wall surface, the effects of major and intermediate principal stresses ${\sigma}_1$ and ${\sigma}_2$ on the yielding and the shape of the deviatoric section are then reflected into the analyses. Performing nonlinear finite element analyses (NLFEA) for the three walls tested in two different studies, their stress-strain response and failure modes are eventually evaluated through the comparisons with the experimental behavior.