• KEPCO Journal on Electric Power and Energy
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• 제1권1호
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• pp.127-134
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• 2015

Recently, the external bonding of carbon fiber reinforced polymer (CFRP) sheets has come to be regarded as a very effective method for strengthening of reinforced concrete structures. The behavior of CFRP-strengthened RC structure is mainly governed by the interfacial behavior, which represents the stress transfer and relative slip between concrete and the CFRP sheet. In this study, the effects of bonded length, width and concrete strength on the interfacial behavior are verified and a bond-slip model is proposed. The proposed bond-slip model has nonlinear ascending regions and exponential descending regions, facilitated by modifying the conventional bilinear bond-slip model. Finite element analysis results of interface element implemented with bond-slip model have shown good agreement with the experimental results performed in this study. It is found that the failure load and strain distribution predicted by finite element analysis with the proposed bond-slip are in good agreement with results of experiments.

• Carbon letters
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• 제17권1호
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• pp.33-38
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• 2016

In the present study, exfoliated graphite nanoplatelets (xGnP) with different particle sizes were coated onto polyacrylonitrile-based carbon fibers by a direct coating method. The flexural properties, interlaminar shear strength, and the morphology of the xGnP-coated carbon fiber/phenolic matrix composites were investigated in terms of their longitudinal flexural strength and modulus, interlaminar shear strength, and by optical and scanning electron microscopic observations. The results were compared with a phenolic matrix composite counterpart prepared without xGnP. The flexural properties and interlaminar shear strength of the xGnP-coated carbon fiber/phenolic matrix composites were found to be higher than those of the uncoated composite. The flexural and interlaminar shear strengths were affected by the particle size of the xGnP, while the particle size had no significant effect on the flexural modulus. It seems that the interfacial contacts between the xGnP-coated carbon fibers and the phenolic matrix play a role in enhancing the flexural strength as well as the interlaminar shear strength of the composites.

• Ocean Systems Engineering
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• 제8권4호
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• pp.409-426
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• 2018

This paper presents the strengthening of tubular joint by wrapping Carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP). In this study, total number of layers, stacking sequence and length of wrapping are the different parameters involved when fiber reinforced polymers (FRP) composites are used for strengthening. For this, parameters where varied and results were compared with the reference joint. The best stacking sequence was identified which has the highest value in ultimate load with lesser deflections. For determining the best stacking sequence, numerical investigation was performed on CFRP composites; length of wrapping and number of layers were fixed. Later, the studies were focused on CFRP and GFRP strengthened joint by varying the total number of layers and length of wrapping. An attempt was done to propose a parametric equation from multiple regression analysis, which can be used for CFRP strengthened joints. Hashin failure criteria was used to check the failure of composites. Results revealed that FRP was having a greater influence in the load bearing capacity of joints, and in reducing the deflections and stresses of joint under axial compressive loads. It was also seen that, CFRP was far better than GFRP in reducing the stresses and deflection.

• Smart Structures and Systems
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• 제19권2호
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• pp.127-136
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• 2017

Fiber reinforced polymer (FRP) has received widespread attention in the field of civil engineering because of its superior durability and corrosion resistance. This article presents the damage mechanisms of a novelty composite called carbon nanofiber modified flax fiber polymer (CNF-modified FFRP). The ability of acoustic emission (AE) to detect damage evolution for different configurations of specimens under uniaxial tension was examined, and some useful AE characteristic parameters were obtained. Test results shows that the mechanical properties of modified composites are associated with the CNF content and the evenness of CNF dispersed in the epoxy matrix. Various damage mechanisms was established by means of scanning electron microscope images. The fuzzy c-means clustering were proposed to classify AE events into groups representing different generation mechanisms. The classifiers are constructed using the traditional AE features -- six parameters from each burst. Amplitude and peak-frequency were selected as the best cluster-definition features from these AE parameters. After comprehensive comparison, a correlation between these AE events classes and the damage mechanisms observed was proposed.

• Structural Engineering and Mechanics
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• 제30권4호
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• pp.403-426
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• 2008

Externally bonding fiber reinforced polymer (FRP) sheets with an epoxy resin is an effective technique for strengthening and repairing reinforced concrete (RC) beams under flexural loads. Their resistance to electro-chemical corrosion, high strength-to-weight ratio, larger creep strain, fatigue resistance, and nonmagnetic and nonmetallic properties make carbon fiber reinforced polymer (CFRP) composites a viable alternative to bonding of steel plates in repair and rehabilitation of RC structures. The objective of this investigation is to study the effectiveness of CFRP sheets on ductility and flexural strength of reinforced high strength concrete (HSC) beams. This objective is achieved by conducting the following tasks: (1) flexural four-point testing of reinforced HSC beams strengthened with different amounts of cross-ply of CFRP sheets with different amount of tensile reinforcement up to failure; (2) calculating the effect of different layouts of CFRP sheets on the flexural strength; (3) Evaluating the failure modes; (4) developing an analytical procedure based on compatibility of deformations and equilibrium of forces to calculate the flexural strength of reinforced HSC beams strengthened with CFRP composites; and (5) comparing the analytical calculations with experimental results.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.371-374
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• 2005

The research reported in this paper provides the test results of eleven reinforced concrete beams strengthened with FRP composites. Three parameters were considered in this investigation: the amount of FRP composites, the types of bonding schemes(continuous sheets or strips), and the material types of FRP composites (Carbon or Glass). The experimental results indicated that because the rupture strain of FRP composites was relatively higher that the yield strain of steel bars, the RC beams strengthened with FRP composites failed due to concrete crushing before the FRP composites arrived at its rupture strain. The compatibility-aided truss model showed reasonable agreement between the predicted and experimental shear stress-strain curves of the beams throughout the entire loading history.

• 폴리머
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• 제27권1호
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• pp.52-60
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• 2003

본 연구에서는 탄소섬유 강화 에폭시 수지 복합재료의 충격 특성 향상을 위해 탄소섬유표면에 전해 및 무전해 니켈도금처리를 하였으며, 이때 각각의 니켈도금법에 따른 충격 특성을 비교 고찰하였다. 도금된 탄소섬유의 표면 특성은 XRD, SEM, 그리고 접촉각 측정을 통해 관찰하였고, 탄소섬유 강화 복합재료의 충격 특성은 Izod형의 충격시험기를 이용하여 분석하였다. 실험결과, 무전해 니켈도금층에는 전해도금층과는 달리 Ni-P 합금이 포함된 것이 XRD를 통하여 확인되었으며, 전해 니켈도금된 탄소섬유가 무전해 니켈도금된 것보다 표면자유에너지가 큰 것이 접촉각 측정을 통해 관찰되었다. 한편, 무전해 니켈도금된 탄소섬유 강화 에폭시 수지 복합재료는 충격강도가 크게 증가하였으나, 전해 니켈도금된 복합재료의 경우는 충격강도가 증가하지 않았다. 이러한 결과는 각각의 도금법에 따른 젖음성의 차이가 탄소섬유 강화 복합재료의 연성을 변화시켜 충격강도 증가에 주요하게 작용되었기 때문으로 사료된다.

• Composites Research
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• 제30권5호
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• pp.316-322
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• 2017

탄소섬유는 매우 우수한 기계적, 전기적, 열적 특성을 가진 소재로써, 고분자를 매트릭스로 하는 복합재료로써 산업적으로 널리 쓰이고 있다. 하지만 이 복합재료는 높은 강도 및 탄성을 가진 탄소섬유에 비해, 약한 고분자 매트릭스로 인한 분리 형상이 약점으로 지적되고 있다. 이를 해결하기 위해 강화재의 첨가가 필수적이다. 그래핀은 매우 우수한 기계적 물성을 지닌 강화재로써, 첨가 시에 높은 물성 향상을 기대할 수 있다. 하지만 그래핀 자체의 응집현상과 고분자 기지와의 약한 결합이 강화효과를 제대로 구현해내지 못하는 결과를 초래하고 있다. 이러한 문제점을 해결하기 위한 핵심 기술로 제시된 것이 기능기화 방법이며, 이를 통해 분산성을 향상시킬 수 있다. 본 연구에서는 멜라민을 이용하여 그래핀 나노플레이틀릿의 기능기화를 진행하고, 이를 에폭시 고분자 기지와 혼합하였다. 제조된 그래핀 나노플레이틀릿/에폭시을 이용하여 탄소섬유 강화 고분자 복합재료를 제조하고 굽힘 특성과 층간전단강도를 측정하였다. 그 결과 복합재료의 기계적 물성이 증가되었으며, 그래핀 나노플레이틀릿의 분산성이 향상됨을 확인하였다.

• Composites Research
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• 제12권3호
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• pp.84-90
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• 1999

HAC/PVA계 MDF시멘트 복합재료의 수분안정성 및 기계적 강도향상을 위하여 불용성 폴리머류(폴리우레탄, 페놀, 에폭시수지)와 탄소섬유(길이3mm)를 1-4wt% 보강하였다. 그리고 가압성형법으로 제조한 복합체의 수분침적 기간별 강도특성(수분안정성)과 계면 및 기계적 특성에 영향을 미치는 폴리머와 시멘트의 가교반응에 대하여 SEM 및 TEM 분석을 통하여 관찰하였다. HAC/PVA계 MDF 시멘트 복합체의 섬유함량에 따른 건조 굽힘강도는 섬유함량이 증가할수록 치밀화 구조가 저하되어 비례적으로 감소되었다. 또한 불용성 폴리머류를 사용한 경우에 건조 굽힘강도는 섬유함량이 증가될수록 저하되는 반면, 수분안정성은 크게 향상되었다. 에폭시 수지를 첨가한 경우에 수분안정성이 가장 우수하였으며, 섬유함량 4% 첨가의 경우에 3일 침적강도가 95%, 7일침적시 87%강도를 유지하였다. 이 점은 폴리머와 시멘트의 금속이온이 가교반응을 일으켜 섬유-메트릭스간 계면 부착강도를 크게 개선되었기 때문으로 추정된다. 반면 인장강도 특성은 모든 불용성 폴리머류 첨가 수준에서 섬유 함량이 증가할수록 비례적으로 증가되었으며, 역시 에폭시 수지 첨가의 경우에 강도특성이 가장 우수하였다. 그리고 섬유함량 4% 첨가된 경우에 있어서 인장강도는 섬유함량 0% 대비 약 30~80% 높게 나타났다.

• 한국초전도ㆍ저온공학회논문지
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• 제12권3호
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• pp.1-6
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• 2010

Since the fiber reinforced polymeric (FRP) composites are considered in next generation of space transportation systems, reliable thermal expansion properties should be well provided for structural design of composite materials. To obtain accurate mechanical behaviors at a cryogenic temperature, precise strain measurement and calibration must be provided. In this work, apparent strains (or thermal output) of temperature self-compensated strain gages were deliberately investigated for epoxy, CTBN modified epoxy and carbon fabric composite system from room temperature to liquid nitrogen temperature. Also, fourth-order thermal output curves were presented for the further calibration. The results showed that the thermal output is heavily dependent on test materials and a large amount of apparent strains were observed for the polymer resins.