• 한국재료학회지
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• 제12권6호
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• pp.442-446
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• 2002

Design of microwave absorbers using high frequency properties of fiber reinforced composites are investigated. Two kinds of composite materials (glass and carbon) are used and their complex permittivity and permeability are measured by transmission/reflection technique using network analyzer. Low dielectric constant and nearly zero dielectric loss are determined in glass fiber composite. However, carbon fiber composites show the high dielectric constant and large conduction loss which is increased with anisotropy of fiber arrangement. It is, therefore, proposed that the glass and carbon fiber composites can be used as the impedance transformer (surface layer) and microwave reflector, respectively. By inserting the foam core or honeycomb core (which can be treated as an air layer) between glass and carbon fiber composites, microwave absorption above 10 dB (90% absorbance) in 4-12 GHz can be obtained. The proposed fiber composites laminates with sandwitch structure have high potential as lightweight and high strength microwave absorbers.

• 한국재료학회지
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• 제23권2호
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• pp.149-153
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• 2013

Delamination crack detection is very important for improving the structural reliability of laminated composite structures. This requires real-time delamination detection technologies. For composite laminates that are reinforced with carbon fiber, an electrical potential method uses carbon fiber for reinforcements and sensors at the same time. The use of carbon fiber for sensors does not need to consider the strength reduction of smart structures induced by imbedding sensors into the structures. With carbon fiber reinforced (CF/) epoxy matrix composites, it had been proved that the delamination crack was detected experimentally. In the present study, therefore, similar experiments were conducted to prove the applicability of the method for delamination crack detection of CF/polyetherethereketone matrix composite laminates. Mode I and mode II delamination tests with artificial cracks were conducted, and three point bending tests without artificial cracks were conducted. This study experimentally proves the applicability of the method for detection of delamination cracks. CF/polyetherethereketone material has strong electric resistance anisotropy. For CF/polyetherethereketone matrix composites, a carbon fiber network is constructed, and the network is broken by propagation of delamination cracks. This causes a change in the electric resistance of CF/polyetherethereketone matrix composites. Using three point bending specimens, delamination cracks generated without artificial initial cracks is proved to be detectable using the electric potential method: This method successfully detected delamination cracks.

• Carbon letters
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• 제19권
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• pp.47-56
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• 2016

In this study, the fracture behavior of a thermoplastic-modified epoxy resin reinforced with continuous carbon fibers for two levels of fiber-matrix adhesion was performed. A carbon fiber with commercial sizing was used and also treated with a known silane, (3-glycidoxy propyl trimethoxysilane) coupling agent. Toughness was determined using the double cantilever test, together with surface analysis after failure using scanning electron microscope. The presence of polysulfone particles improved the fracture behavior of the composite, but fiber-matrix adhesion seemed to play a very important role in the performance of the composite material. There appeared to be a synergy between the matrix modifier and the fiber-matrix adhesion coupling agent.

• Composites Research
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• 제28권4호
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• pp.168-175
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• 2015

탄소섬유 강화 복합재료는 높은 비강도 및 비강성을 가지기 때문에 자동차 산업, 선박, 우주 항공 산업과 같은 다양한 산업 분야에 적용되어 왔으며, 수요가 점차 증가하고 있다. 탄소섬유 강화 복합재료에는 기지재로 주로 에폭시(Epoxy)와 같이 점도가 낮고 젖음 특성이 우수하며 강도가 양호한 열경화성(Thermosetting) 수지가 사용된다. 열경화성 수지는 우수한 물리적 특성을 나타내지만 재사용이 어렵다. 이러한 문제를 해결하기 위하여 재사용이 가능한 탄소섬유 강화 열가소성 수지(Thermoplastic) 복합재료 개발 및 탄소섬유 재사용에 관한 많은 연구들이 진행되고 있다. 본 연구에서는 열분해 방법을 사용하여 탄소섬유/에폭시 복합재료로부터 탄소섬유와 수지를 분리하여 탄소섬유를 재활용하였다. 에폭시의 분해도(Degree of decomposition)는 열중량분석기(TGA)와 시차 주사현미경(SEM)을 통해 확인하였다. 수지로부터 분리해낸 탄소섬유는 절단(Cutting)과 그라인딩(Grinding) 방법을 거쳐 탄소섬유 복합재료 시트(Sheet)를 제조하였다. 재활용 탄소 섬유로 제조된 탄소섬유 시트는 각각 다른 냉각조건에서 결정화 엔탈피(Crystallization enthalpy)와 기계적 특성, 표면과 단면의 형태를 분석하였다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.131-134
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• 2002

Braided carbon fiber reinforced Al matrix composites were developed and characterized. Braided carbon fiber preforms with braiding angles of $30^{\circ}$, $45^{\circ}$ and $60^{\circ}$ were manufactured by using a braiding machine. The manufactured braided carbon fibers were used as reinforcement to fabricate Al matrix composites by employing a pressure infiltration casting method. In the processing of pressure infiltration casting, important processing parameters such as melting temperature, preheating temperature of preform and applied pressure were optimized. Prediction of elastic constants on composites was performed by using the volume averaging method, which utilizes the coordinate transformation and the averaging of stiffeness and compliance constants based upon the volume of each reinforcement and matrix material. The elastic moduli of composites were evaluated by using Resonant Ultrasound Spectroscopy(RUS) method and compared with the elastic moduli obtained from static tensile test method.

• 융복합기술연구소 논문집
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• 제8권1호
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• pp.27-31
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• 2018

The age of electric vehicle is coming. One of the most important problems to be solved for popularization of electric vehicle is fuel economy. To increase fuel economy of electric vehicles, it is necessary to improve the performance of the battery or the car body should be lighter than now. To solve the problem of the car body, change the car body's material to carbon fiber reinforced composites can be an excellent answer. However, the part made from carbon fiber reinforced composites is vulnerable to accidents due to their high brittleness. In this study, ductile silica fume was added into the carbon fiber composites to enhance toughness. To examine this, various amounts and sizes of silica fume were considered and the toughness enhancement was examined by performing tensile tests.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.89-92
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• 2001

Drop weight impact tests were performed to investigate the impact behavior of carbon fiber/epoxy composite laminates reinforced by short fibers and other interleaving materials. Characterization techniques, such as cross-sectional fractography and scanning acoustic microscopy, were employed quantitatively to assess the internal damage of some composite laminates. Scanning electron microscopy was used to observe impact damage and fracture modes on specimen fracture surfaces. The results show that composite laminates experience various types of fracture; delamination, intra-ply cracking, matrix cracking and fiber breakage depending on the interlayer materials. Among the composite laminates tested in this study, the composites reinforced by Zylon fibers showed very good impact damage resistance with medium level of damage, while the composites interleaved by poly(ethylene-co-acrylic acid) (PEEA) film is expected to deteriorate the bulk strength due to the reduction of fiber volume fraction, even though the damaged area is significantly reduced.

• Fibers and Polymers
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• 제5권1호
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• pp.31-38
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• 2004

In the present paper, a variety of fiber reinforcements, for instance, stabilized OXI-PAN fibers, quasi-carbon fibers, commercial carbon fibers, and their woven fabric forms, have been utilized to fabricate pseudo-unidirectional (pseudo-UD) and 2-directional (2D) phenolic matrix composites using a compression molding method. Prior to fabricating quasi-carbon fiber/phenolic (QC/P) composites, stabilized OXI-PAN fibers and fabrics were heat-treated under low temperature carbonization processes to prepare quasi-carbon fibers and fabrics. The thermal conductivity and thermal expansion/contraction behavior of QC/P composites have been investigated and compared with those of carbon fiber/phenolic (C/P) and stabilized fiber/phenolic composites. Also, the chemical compositions of the fibers used have been characterized. The results suggest that use of proper quasi-carbonization process may control effectively not only the chemical compositions of resulting quasi-carbon fibers but also the thermal conductivity and thermal expansion behavior of quasi-carbon fibers/phenolic composites in the intermediate range between stabilized PAN fiber- and carbon fiber-reinforced phenolic composites.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1322-1325
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• 2005

The main objectives of this research work are to develop conductive glass fiber woven roving and carbon fiber unidirectional fabric composite materials and to determine their electromagnetic shielding effectiveness(EMSE). Epoxy is the matrix phase and glass, carbon fiber are the reinforcement phase of the composite material. Carbon black are incorporated as conductive fillers to provide the electromagnetic shielding properties of the composite material. The amount of carbon black in the composite material is varied by changing the carbon black composition, woven roving and unidirectional (fabric) structure. The EMSE of various fabric composites is measured in the frequency range from 300MHz to 800MHz. The variations of EMSE of woven roving and unidirectional composites with fabric structure, metal powder composite are described. Suitability of conductive fabric composites for electromagnetic shielding applications is also discussed.

• 한국재료학회지
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• 제31권11호
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• pp.626-634
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• 2021

Cu matrix composites reinforced with chopped carbon fiber (CF), which is cost effective and can be well dispersed, are fabricated using electroless plating and hot pressing, and the effects of content and alignment of CF on the thermal properties of CF/Cu composites are studied. Thermal conductivity of CF/Cu composite increases with CF content in the in-plane direction, but it decreases above 10% CF; this is due to reduction of thermal diffusivity related with phonon scattering by agglomeration of CF. The coefficient of thermal expansion decreases in the in-plane direction and increases in the through-plane direction as the CF content increases. This is because the coefficient of thermal expansion of the long axis of CF is smaller than that of the Cu matrix, and the coefficient of thermal expansion of its short axis is larger than that of the Cu matrix. The thermal conductivity is greatly influenced by the agglomeration of CF in the CF/Cu composite, whereas the coefficient of thermal expansion is more influenced by the alignment of CF than the aggregation of CF.