• Composites Research
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• v.16 no.3
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• pp.49-57
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• 2003

This paper presents the tensile characteristics for carbon/epoxy, carbon/phenolic and silica/phenolic composites under elevated temperature, which are considered for vehicle structure or thermal protection materials. The tensile test was conducted with servo-hydraulic testing machine and high temperature furnace, and the mechanical properties such as tensile strength, elastic modulus and Poisson's ratio were evaluated by using high temperature strain gages. Also, they were compared each other with respect to fiber orientation and temperature effect. These test results were used for designing and analyzing some airframe structures with these composites.

• Composites Research
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• v.18 no.3
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• pp.14-20
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• 2005

This paper presents a study on the permittivities of the carbon black/epoxy composite at microwave frequency. The measurements were performed at the frequency band of $1\;GHz\~18\;GHz$. The experimental data show that the complex permittivities of composites depend strongly on the natures and concentrations of the carbon black dispersion. The frequency characteristics of dielectric constants and ac conductivities of composites show the good conformity with descriptions of the percolation theory, satisfying the general scaling relation. The measuring frequency band is over the critical frequency, below that the ac conductivities of composites are constant to the frequency. The values of dielectric constants and ac conductivities have consistent relationships with the carbon black concentration. The A new scheme, that is a branch of Lichtenecker-Rother formula, is proposed to obtain a mixing law to describe the complex permittivities of the composites as function frequency and concentration of carbon black.

• Composites Research
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• v.16 no.2
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• pp.48-53
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• 2003

This paper presents a study on the permittivities of the I-glass fabric/epoxy composite laminates containing carbon black dispersions at microwave frequency. Measurements were performed at the frequency band of 5 GHz∼18 GHz. The results showed that the complex permittivities of the composites depend strongly on the natures and concentrations of the carbon black dispersion. A new scheme is proposed to obtain a mixing law for the estimation of the complex permittivities of the composite laminates as a function of concentration of carbon black. Simultaneously, the complex permittivity of carbon black itself was also calculated by the scheme. The experimental values of the complex permittivities of the composites were compared to those calculated.

• Composites Research
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• v.14 no.6
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• pp.38-46
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• 2001

In this study, An optimization code that can design microwave absorbing composite laminates is developed, and 3-layered microwave absorbing composite laminates are developed by optimizing the thickness of each layer. The layers are 3 different composite laminates. Many variables including lay-up angles of electromagnetically orthotropic composite layer can be considered in this code. The developed laminate is composed of an impedance matching layer of glass/epoxy fabric laminate, a glass/epoxy fabric laminate layer containing aluminum filler and carbon/epoxy fabric laminate layer. Permittivities of the materials are obtained using a network analyzer and a coaxial air line.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.144.2-144.2
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• 2010

Bipolar plate는 고분자 전해질 연료전지(PEMFC)에서 핵심 부품 중의 하나이고, 전해질 막이나 촉매 등에 비해서는 상대적으로 쉽게 접근할 수 있기 때문에 많은 연구가 수행되고 있다. Bipolar plate를 제조하는 기술은 크게 금속을 프레스 가공하는 방법, graphite 판을 직접 밀링하는 방법 및 고분자/카본계의 press molding 법 등 3가지로 분류되며, 본 연구에서는 3번째 방법에 의해서 bipolar plate를 대량 생산하는 방법에 대해 연구하였다. 고분자 매트릭스는 에폭시계 수지를 사용하였고, 카본계 재료는 graphite 분말과 carbon nanotube를 사용하였다. 이들 재료들을 일정한 비율로 혼합한 후 differential scanning calorimetry(DSC)를 사용하여 열분석 하였고, 그 결과를 Kissinger equation에 대입하여 경화반응 속도론을 연구하였다. 또한, 경화된 에폭시/탄소 복합재료의 전기전도도, 유리전이온도, 표면에너지 특성 등을 분석하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1268-1272
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• 2000

본, 논문에서는 카본/에폭시, PZT 세라믹 박판, 글래스/에폭시 층으로 이루어진 곡면형 복합재료 작동기(LIPCA)의 설계, 제작 및 성능실험에 대한 연구 성과를 제시하고 있다. LIPCA의 큰 요점은 기존 THUNDER의 성능을 유지하면서 이를 경량화 하기 위하여 THUNDER의 금속 층을 상대적으로 가벼운 섬유 강화 복합재료로 대체하는 것이다. 이러한 경량화 작업으로 LIPCA는 기존 THUNDER 보다 약 $30{\sim}40%$ 정도의 무게를 감소시킬 수 있으며, 복합재료의 특성에 따라 설계의 유연성을 가질 수 있는 장점이 있다. 또한, 에폭시 수지를 사용함으로써 접착제 없이 평판 몰드에서 오토클레이브에서 $177^{\circ}C$로 경화되어, 탈형된 후 충분한 곡률을 형성하였다. 작동 성능 실험에서, LIPCA는 기존 THUNDER보다 작동변위가 향상됨을 보였다.

• Polymer(Korea)
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• v.28 no.4
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• pp.285-290
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• 2004

Nondestructive damage sensitivity of carbon nanotube(CNT) and nanofiber (CNF)/epoxy composites with their adding contents was investigated using electro-micromechanical technique. Carbon black (CB) was used only for the comparison with CNT and CNF. The fracture of carbon fiber was detected by acoustic emission (AE), which was correlated to the change in electrical resistance, ΔR under double-matrix composites (DMC) test. Stress sensing on carbon nanocomposites was performed by electro-pullout test under uniform cyclic loading. At the same volume fraction, the damage sensitivity for fiber fracture, matrix deformation and stress sensing were highest for CNT/epoxy composite, whereas for CB/epoxy composite they were the lowest among three carbon nanomaterials (CNMs). Damage sensitivity was correlated with morphological observation of carbon nanocomposites. Homogeneous dispersion among CNMs could be keying parameters for better damage monitoring. In this study, damage sensing of carbon nanocomposites could be evaluated well nondestructively by the electrical resistance measurement with AE.

• Composites Research
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• v.17 no.3
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• pp.38-44
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• 2004

The electromagnetic interference (EMI) shielding is very essential for commercial and military purposes. We fabricated multi-walled carbon nanotube (MWNT)/epoxy composites and studied the electromagnetic characteristics of the composites before we study the characteristics of MWNT-added glass fiber-reinforced composites. After setting up the fabrication process, we measured the permittivity of MWNT/epoxy composites with process variables and MWNT concentrations in X-band (8.2GHz~12.4GHz). We also observed re-aggregation phenomenon of MWNTs and investigated its effect on the permittivity. The permittivity of the composites was influenced by the degree of dispersion of MWNTs and increased almost linearly as MWNT concentration increases.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.135-138
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• 2000

본 논문에서는 열팽창계수(CTE)가 거의 없는 카본게폭시, PZT 세라믹 박판, 그리고 열팽창계수가 큰 글래스/에폭시 층으로 이루어진 곡면형 복합재료 작동기(LIPCA)의 설계, 제작 및 성능실험에 대한 연구성과를 제시하고 있다. LIPCA의 른 요점은 기존 THUNDER의 성능을 유지하면서 이를 경량화 하기 위하여 THUNDER의 금속 층을 상대적으로 가벼운 섬유 강화 복합재료로 대체하는 것이다. 이러한 경량화 작업으로 LIPCA는 기존 THUNDER 보다 약 30~40% 정도의 무게를 감소시킬 수 있으며, 복합재료의 특성에 따라 설계의 유연성을 가질 수 있는 장점이 있다. 또한, 에폭시 수지를 사용함으로써 접착제 없이 평판 몰드에서 오토클레이브에서 177$^{\circ}C$로 경화되어, 탈형된 후 충분한 곡률을 형성하였다. 작동 성능 실험에서, LIPCA는 기존 THUNDER보다 작동변위가 향상됨을 보였다.

• Composites Research
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• v.23 no.5
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• pp.15-21
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• 2010

In this study, repair and maintenance schemes of the damaged composite structure was investigated, and a repair process of the carbon/epoxy laminate composite structure was investigated numerically and experimentally. The composite laminates were damaged by drop weight type impact test machine. The damaged composite structure was repaired using external patch repair method after removing damaged area. The compressive strength test and analysis results after repairing the impact damaged specimens were compared with the compressive strength test and analysis results of undamaged specimens and impact damaged specimens. Finally, the strength recovery capability by repairing were investigated.