• Composites Research
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• v.12 no.3
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• pp.8-16
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• 1999

Carbon woven fabric/C/SiC composites were fabricated by multiple impregnations of carbon woven fabric/carbon preform with the polymer precursor of SiC, i.e., polycarbosilane. In addition, two kinds of low density carbon/carbon preforms which had different fiber volume fraction and fiber orientation, i.e., a carbon woven fabric(${\thickapprox}$55 vol%)/carbon and a chopped carbon fiber${\thickapprox}$40 vol%)/carbon composites, were reaction-bonded with a silicon melt at 1$700^{\circ}C$ in a vacuum to fabricate dense carbon fiber/Si/SiC composites. The reaction-bonding process increased the density to ~2.1 g/$cm^3$ from 1.6 g/$cm^3$ and 1.15 g/$cm^3$ of a carbon woven and a chopped carbon preforms, respectively. All of the composites fractured with extensive fiber pull-out. The higher the density the higher the stiffness and proportional limit stress. The mechanical properties obtained from a three-point bend and tension tests were compared. The ratios of the peak tensile stresses to the bending strengths of a carbon woven and a chopped carbon composites were about one-third, respectively. The carbon woven fabric/Si/SiC composites with density of 2.06 g/$cm^3$ showed ~120 MPa of ultimate strength and ~80 MPa of proportional limit in bend testing.

• Composites Research
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• v.33 no.3
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• pp.101-107
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• 2020

This study investigates the characterization on the thermal insulation properties of silicon carbide coating on the C_f-C composites. The silicon carbide coatings by chemical vapor deposition on the C/C composites are prepared to evaluate thermal resistance. Firstly, we perform the basic insulation test by thermal shock at 1350℃ in air on the C/C composite and SiC-coated C/C composite. We also performed the burner tests on the surface of the composites at high temperatures such as 1700 and 2000℃, and the weight change after burner tests are measured. The damages on the surface of C/C composite and SiC-coated composite are observed. As a result, the SiC coating is beneficial to protect the C/C composite from high temperature even though damages such as defoliation, crack and voids are observed during burner test at 2000℃.

• Composites Research
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• v.18 no.3
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• pp.1-6
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• 2005

Carbon nanofiber exhibits superior and of ien unique characteristics of mechanical, electrical, chemical and thermal properties. Despite of the excellent properties of carbon nanofiber, the properties of carbon nanofiber filled polymer composites were not increased largely. The reason is that it is still difficult to ensure the uniform dispersion of carbon nanofiber in a polymer matrix. In this study, for improvement of the mechanical properties of composites, carbon nanofiber reinforced hybrid composites was investigated. For the dispersion of carbon nanofiber. solution blending method using ultrasonic was used. Dispersion of carbon nanoifiber was observed by scanning electron microscope (SEH). Mechanical properties were measured by universal testing machine(UTM).

• Korean Journal of Materials Research
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• v.7 no.8
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• pp.687-693
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• 1997

4방향성(4D)탄소섬유 프리폼을 각각 polyfurfury1 alcohol과 석탄계 핏치로 함침하는 방법과 CVI방법에 의하여 열분해 탄소로 증착하는 방법을 채택하여 4방향성 탄소/탄소 복합재를 제작하였다. 아크플라즈마 토치 및 지상연소 시험에 의하여 이들의 삭마특성을 비교 관찰하였다. 4D 탄소/탄소 복합재의 기공도는 밀도가 증가할 수록 감소하였으며, 고밀도화된 시편일 수록 삭마저항성이 우수하게 나타났다. CVI-핏치계 4D 탄소/탄소 복합재가 내삭마 성능이 가장 우수하였다. 삭마거동은 결합재의 종류와 복합재의 밀도 및 기공도에 크게 의존함을 알 수 있었다.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.118-123
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• 1999

저밀도 폐놀계 탄소/탄소 복합재의 층간전단강도를 개선하기 위해 흑연분말, 카본블랙, 카본매트, 단섬유 등의 첨가제를 사용하였다. 카본매트와 단섬유를 첨가한 경우, 수지의 부족에 의한 층간접착력의 약화를 가져왔으며, 카본블랙을 첨가한 경우에도 큰 효과를 나타내지 못했다. 흑연을 첨가했을 때 약 30%의 층간강도 개선을 가져왔으며 특히 9 vol.%의 첨가량에 대해서 가장 큰 효과를 보였다.

• Composites Research
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• v.13 no.2
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• pp.22-29
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• 2000

Although C/C composites have excellent mechanical properties at high temperature, the disadvantage of oxidation in air restricts their applications. Thus a lot of investments have been studied to improve this drawback. In this study, SiC used as a thermal protective coating material possesses almost the same expansion coefficient compared to that of carbon, so SiC was coated on 4D C/C composites by Pack-Cementation process. For SiC-coated C/C composites, optical microscopy observations were performed to estimate the conversion mechanism involved and air oxidation tests were also performed to evaluate the improvement of oxidation resistance. Afterwards the optimum conditions of coating process were estimated from the results of several analysis and tests.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.554-557
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• 2010

본 논문에서는 동일한 체적분율 가지는 탄소나노튜브 나노복합재의 기계적 특성을 규명하였다. 동일한 chirality를 가지는 서로 다른 크기의 탄소나노튜브를 이용하여 탄소나노튜브의 크기가 복합재의 물성에 미치는 영향을 규명하였다. 복합재료의 분자동역학의 결과 탄소나노튜브의 길이방향의 물성은 크게 증가하나, 전단특성의 물성 강화효과를 나타나지 않았다. 이는 통해 탄소나노튜브와 기지재료 사이의 상호작용력이 복합재료의 전단력을 전달하고, 변형을 유지할 만큼 강하지 않다는 것을 확인하였다. 이와 같은 분자동역학 결과를 바탕으로 멀티스케일 모델을 개발하여 복합재료에서 나타나는 현상을 묘사하였다. 제안된 멀티스케일 모델을 이용하여 다양한 조건의 복합재료에 대한 특성 예측이 가능하다.

• Composites Research
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• v.13 no.2
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• pp.72-80
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• 2000

Effect of graphite powder addition on the mechanical properties of carbon fiber reinforced carbon composites (C/C composites) was investigated. Greenbody (G/B) with 0~30wt.% graphite powder addition to phenol resin was prepared and carbonized at $1000^{\circ}C$ to make C/C composites. Flexural strengths of 20wt.% graphite powder additions showed maximum values in the both case of G/B and C/C composites. But, at the graphite addition over 20wt.%, there was negative effect due to the matrix inhomogeneity. Flexural strength of cured resin without graphite Powder was higher than that with graphite. However, flexural strength of carbonized resin with graphite increased three times as much as that of carbonized resin without graphite. Because the addition of graphite powder effects the restraint of shrinkage after carbonization and the deflection of crack path. In Mode II ENF test, energy release rates($G_{II}$) of G/B and C/C composites with the 20w1.% addition of graphite were both increased. But, the addition of graphite was more effective to the increase of $G_{II}$ in C/C composites than that in G/B.

• 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.

• Polymer(Korea)
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• v.24 no.2
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• pp.237-244
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• 2000

Phenolic resin used as a precursor of carbonized matrix for carbon-carbon composites was modified by addition of molybdenum disilicide (MoSi$_2$) in various concentrations of 0, 4, 12 and 20% by weight to improve the anti-oxidation properties of the composites. The green body was manufactured by a prepreg method and was submitted to carbonization up to 110$0^{\circ}C$. In this work, the oxidation behavior of carbon-carbon composites with MoSi$_2$ as an oxidation inhibitor was investigated at the temperature range of 600-100$0^{\circ}C$ in an air environment. The carbon-carbon composites with MoSi$_2$ showed a significantly improved oxidation resistance due to both the reduction of the porosity formation and the formation of mobile diffusion barrier for oxygen when compared to those without MoSi$_2$. Carbon active sites should be blocked, decreasing the oxidation rate of carbon. This is probably due to the effect of the inherent MoSi$_2$ properties, resulted from a formation of the protective layer against oxygen attack in the composites studied.