• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.115-123
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• 2007

For investigating self-diagnosis applicability, a method based on monitoring the changes in the electrical resistance of carbon fiber reinforced concrete has been tested. Then after examining change in the value of electrical resistance at each flexural weight-stage of carbon fiber in CFGFRP (carbon fiber and glass fiber reinforcing plastic) with new type rib and carbon sheet for concrete reinforcing, the correlations of electrical resistance and load as a function of strain, deflection were analyzed. As the results, it is clarified that when carbon fiber rod, rib and sheet fracture, the electrical resistance of it increase largely, and specially in case of CFGFRP, afterwards glass fiber tows can be resist the load due to the presence of the hybrid (carbon and glass) reinforced fiber. Therefore, it can be recognized that reinforcing bar and new type rib of CFGFRP and sheet of CF could be applied for self-diagnosis of fracture in reinforced FRP concrete.

• Journal of the Korea Concrete Institute
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• v.23 no.4
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• pp.405-411
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• 2011

Using combinations of carbon and glass fiber composites normally used for strengthening of concrete structures, the hybrid effect from strengthening concrete structures using the composite is studied. To produce the hybrid effects, the specimens were made with optimum proportions of carbon fibers with glass fibers. Then, direct tensile tests were conducted on the hybrid FRP (fiber reinforced polymer) specimens. Unlike the woven fiber sheet currently used in construction sites, the FRP specimens have to be directly combined with the fibers, which make the work very complicated. Therefore, direct tensile test specimens manufacturing method based on the combination of high-tension carbon fibers and E-type glass fibers was proposed and the effects of hybridization is studied through the direct tensile test. By comparing the ductility index, the modulus of elasticity, and the stress-strain curves of the specimens, the most optimum glass to carbon fiber combination ratio for the hybrid FRP was found to be 9 to 1 with ductile K-type epoxy. The study results are discussed in detail in the paper.

• Journal of the Korea Concrete Institute
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• v.21 no.1
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• pp.47-53
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• 2009

12 concrete blocks, on which hybrid fibrous sheets (carbon fiber and glass fiber) had been bonded, were subjected to tensile load in order to estimate properties of the bonded interface. the sheet length was varied by 100mm, 200mm and 400mm. It was found that more than 150mm bond length is required to achieve the maximum bearing capacity of the interface. In this study, maximum bond stress $\tau_{F,max}$, ultimate slip $S_{FU}$ of the interface were estimated $\tau_{F,max}$=3.0MPa and $S_{FU}$= 0.175mm, respectively.

• Journal of the Korea Concrete Institute
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• v.20 no.2
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• pp.239-247
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• 2008

Use of both carbon fiber (CF) and glass fiber (GF) at the same time to strengthen existing flexural members was exploited. Using a proper volumetric GF / CF ratio, the CF can rupture first followed by subsequent rupture of GF at higher stress and strain showing a pseudo-ductile behavior. A theoretical study indicated that the ratio is 4.62 : 1 and higher where the pseudoductile effect can be shown. Flexural tests of plain concrete beams strengthened using fibers were first carried out. Hybrid FRP sheet using 8.8 : 1 ratio was then fabricated and the sheet was used to strengthen reinforced concrete beams. The RC beams strengthened using 1-ply and 2-ply hybrid sheets both revealed increased strength over a non-strengthened beam and ductile flexural behavior. A comparable beam strengthened using CF also showed increased strength but with limited ductility.

• Composites Research
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• v.28 no.4
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• pp.168-175
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• 2015

Recently, the applications of carbon fiber reinforced plastics (CFRPs) have become broader than ever when it comes to such industries as automotive, ships, aerospace and military because of their lightweight-ness and high mechanical properties. Thermosetting plastics like epoxy are frequently used as the binding matrix in CFRPs due to their high hardness, wetting characteristics and low viscosity. However, they cannot melted and remolded. For this reason, thermosetting plastic wastes have caused serious environmental problems with the production of fiber reinforced plastics. Thus, many studies have focused on the carbon fiber reinforced thermoplastics (CFRTPs) and recycling carbon fiber. In this study, recycled carbon fiber (RCF) was prepared from CFRPs using a pyrolysis method, which was employed to separate resin and carbon fiber. The degree of decomposition for epoxy resin was confirmed from thermal gravimetric analysis (TGA) and scanning electron microscope (SEM). The RCF was cut and ground to prepare a carbon fiber composite sheet (CFCS). CFCS was manufactured by applying recycled carbon fibers and various thermoplastic fibers. Various characterizations were performed, including morphological analyses of surface and cross-section, mechanical properties, and crystallization enthalpy of CFCS at different cooling conditions.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.2
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• pp.227-234
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• 2010

To investigate the flexural behavior of RC beams strengthened with carbon fiber sheets, 1 control beam and 8 strengthened beams(4 NU-beams without U-shaped band and 4 U-beams with U-shaped band) are tested. The variables of experiment are composed of the number of carbon fiber sheets and the existence of U-shaped band, etc. The experimental results showed that the strengthening system with U-shaped band controls the premature debonding and provides a more ductile failure mode than the strengthening system without U-shaped band. It can be found from the load-deflection curves that as the number of fiber sheets is increased, the maximum strength and the flexural rigidity is increased. The experimental results are compared with the analytical results of nonlinear flexural behaviors for strengthened RC beam. The proposed analytical method for strengthened beams is proved to be accurate by an experimental investigation of load-deflection curve, yield load, maximum load, and flexural rigidities in the pre- and post-yielding stages.

• Proceedings of the Korean Fiber Society Conference
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• 2003.04a
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• pp.309-310
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• 2003

활성탄소 (activated carbons, ACs)는 넓은 비표면적을 가지고 있어 흡착용량이 크며, 발달된 미세공을 가지고 있기 때문에 오염물질의 제거능력이 높을 뿐만 아니라 경제적, 환경 친화적인 측면에서도 유리하다. 특히 섬유화된 할성탄소섬유 (activated carbon fibers, ACFs)는 균일한 세공이 표면에 노출되어 있어 흡착속도가 빠르며, 안정성과 재생성이 좋고 섬유상이기 때문에 가공이 용이하며 직포, 부직포, 시트 등의 형태로 만들어져 용매회수, 공업제품의 정제, 오폐수의 처리시설, 소각시설의 유해 배기가스의 흡착등에 널리 사용되고 있다.[1,2] (중략)

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1997.11a
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• pp.171-176
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• 1997

본 연구에서는 노후화 된 구조물을 효과적으로 보강할 수 있는 방법에 대해 휨 거동을 중심으로 그 성능을 규명하고자 하였다. 연구에 채택된 보강재료로는 현재 시공의 간편성과 보강된 부재 단면의 최소화로 최근에 각광을 받고 있는 섬유접착 보강재료 중에서 탄소섬유쉬트(CFS)와 아라미드섬유쉬트(AFS) 접착공법을 선택하였으며, 현재 상용중인 보강단면을 채택하여 보수ㆍ보강을 실시하였다. 그리고, 보강효과를 실험을 통하여 비교ㆍ분석함으로써 합리적인 보수ㆍ보강공법을 위한 선택의 폭을 넓히고, 현재 활발히 진행중인 국내 보수ㆍ보강의 체계화를 위한 기초적인 자료를 얻고자 한다. (중략)

• Composites Research
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• v.26 no.1
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• pp.14-20
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• 2013

The electrospun PVDF containing CNT was made for fabricating materials of the actuator. The electrochemical and their actuating movement were evaluated for the actuator performance in the electrochemical environment. The actuator (which was fabricated by electrospinning) had some advantages, i.e., good dispersion and flexible properties. In the electrospinning process, the final product would have different forms based on different essential factors. In this work, electrospun nanofibers were aligned by using the drum-type collector, and the morphology was identified via the field emission-scanning electron microscope (FE-SEM). The uniform dispersion of CNT in PVDF nanofiber was observed by electron probe X-ray micro-analysis (EPMA) test. The results of tensile strength and electrical resistivity provided the aligned state. The electrospun CNT/PVDF nanofiber sheet on the aligned direction showed better mechanical and electrical properties than the case of the vertically-aligned direction. The efficiency and electrical capacities of electrospun CNT/PVDF nanofiber sheets were compared with the cast PVDF sheet for actuator application. Electrospun CNT/PVDF nanofiber sheet exhibited much better the case of actuator performance than cast neat PVDF actuator, due to the excellent electrical connecting areas.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.2
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• pp.69-77
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• 2009

The experiment was carried out to investigate lateral retrofitting effects by FRP and BRB (Buckling-Restrained Brace) for beam-column elements. These results were utilized to establish an analytical model using commercial nonlinear analysis software, PERFORM3D. Concrete and steel analytical models previously proposed by several scholars were adopted for this analytical study. A proposed analysis model showed reasonable accuracy compared with the test results on the beam-column elements strengthened FRP sheets and BRB, as well as with the non-strengthened element subjected to lateral cyclic loadings. Subsequently, the proposed modeling technique for nonlinear analysis would be helpful for preliminary analyses for retrofitting structures, by enabling engineers to estimate the improved capacity of retrofitted structural elements before performing construction.