• Carbon letters
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• v.17 no.1
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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.

• Structural Engineering and Mechanics
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• v.88 no.3
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• pp.201-208
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• 2023

In this work, the effect of the correction fibers direction on the efficiency of repairing damaged composite plates was highlighted. The composite plates studied in this work consist of eight layers of graphite/epoxy, while the patch used in this repair consists of four layers of the same type. The results obtained in this work, whether with regard to the experimental or analytical side, showed that the fibers orientation affects the repair efficiency, so the closer the angle of fibers inclination is to the tensile strength direction, the performance of the composite material is ideal. Hence, we conclude that the composite materials with longitudinal fibers (Parallel to tensile strength) is the most powerful and efficient material in performance.

• Composites Research
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• v.37 no.3
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• pp.162-169
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• 2024

In this study, PAN(polyacrylonitrile)-based precursor fibers were produced through a wet-spinning process, and their morphologies and graphitization behavior were investigated in the presence of two graphitization catalysts (Ca, Ni). The graphitization catalysts were introduced into the formed pores during hot-water stretching of wet-spun PAN-based precursor fibers. The catalytic effects of graphitization catalysts were examined through crystal structure and Raman analysis. At a relatively low temperature of 1500℃, the graphitization was not significantly affected, whereas at a high temperature of 2400℃, the obtained I_D/I_G value of graphite fiber (GF-Ni100) was decreased by about twice (~0.28) compared to the untreated fibers (GF-AS~0.54). By comparing the I_D/I_G values (GF-Ca100~0.42: GF-Ni100~0.28) of Ca and Ni graphitization catalyst, it was found that the degree of graphitization of Ni graphitization catalyst showed higher influence than that of Ca graphitization catalyst. Moreover, 2D band was also observed, indicating that the graphite plane structures composed of multiple layers were developed. XRD results confirmed that the crystal inter-planar distance (d₀₀₂) of the graphite crystal was slightly decreased after the treatment with the graphitization catalyst, But, the crystal size of Ca-treated graphite fiber (GF-Ca100) was increased by up to ~5 nm.

• Composites Research
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• v.25 no.3
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• pp.82-89
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• 2012

This paper investigated the composite materials application examples and trends in the future to the solid rocket motor cases. The motor case must be stiff and tolerate at the high pressures, and light weight. In accordance to these kind of requirements, the composite materials showed the adaptable efficiency, and glass fibers, aramid, carbon fibers are applied to orderly. The comparison of the motor case efficiencies of the D6AC steel alloy, aramid, carbon fibers results in the carbon fibers best. Also the capacity of the payload will be increased more than 20% by using the high strength ones.

• Tribology and Lubricants
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• v.5 no.2
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• pp.94-100
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• 1989

Friction and Wear behavior of continuous graphite fiber composites was studied for different fiber orientations against the sliding direction. The effect of fiber orientation on friction and wear of the composite and on the deformation of the counterface was investigated experimentally. Pin on disk type testing machine was built and employed to generate the friction and wear data. A graphite fiber composite plate was produced by the bleeder ply molding in an autoclave and machined into rectangular pin specimens with specific fiber orientations, i.e., normal, transverse, and longitudinal directions. Three different wear conditions were employed for two different periods of time, 24 and 48 hours. The wear track of the worn specimens and the metal counterface was examined with a scanning electron microscope (SEM) to observe the damaged fibers on the surface and wear film generation on the counterface. Wear mechanism of the composite during sliding wear is proposed based on the experimental results.

• Carbon letters
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• v.24
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• pp.97-102
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• 2017

Graphite fibers are materials with a high specific modulus that have attracted much interest in the aerospace industry, but their high manufacturing cost and low yield are still problems that prevent their wide applications in practice. This paper presents a laser-based process for graphitization of carbon fiber (CF) and explores the effect of laser radiation on the microstructure of CF. The obtained Raman spectra indicate that the outer surface of CF evolves from turbostratic structures into a three-dimensional ordered state after being irradiated by a laser. The X-ray diffraction data revealed that the growth of crystallite was parallel to the fiber axis, and the interlayer spacing $d_{002}$ decreased from 0.353 to 0.345 nm. The results of scanning electron microscopy revealed that the surface of irradiated CFs was rougher than that of the unirradiated ones and there were scale-like small fragments that had peeled off from the fibers. The tensile modulus increased by 17.51% and the Weibull average tensile strength decreased by 30.53% after being irradiated by a laser. These results demonstrate that the laser irradiation was able to increase the graphitization degree of the CFs, which showed some properties comparable to graphite fibers.

• Carbon letters
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• v.19
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• pp.1-11
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• 2016

In efforts to characterize and understand the properties and processing of phenylethynyl-terminated imide (LaRC PETI-5, simply referred to as PETI-5) oligomers and polymers as a high-temperature sizing material for carbon fiber-reinforced polymer matrix composites, PETI-5 imidization and thermal curing behaviors have been extensively investigated based on the phenylethynyl end-group reaction. These studies are reviewed here. In addition, the use of PETI-5 to enhance interfacial adhesion between carbon fibers and a bismaleimide (BMI) matrix, as well as the dynamic mechanical properties of carbon/BMI composites, are discussed. Reports on the thermal expansion behavior of intercalated graphite flake, and the effects of exfoliated graphite nanoplatelets (xGnP) on the properties of PETI-5 matrix composites are also reviewed. The dynamic mechanical and thermal properties and the electrical resistivity of xGnP/PETI-5 composites are characterized. The effect of liquid rubber amine-terminated poly(butadiene-co-acrylonitrile) (ATBN)-coated xGnP particles incorporated into epoxy resin on the toughness of xGnP/epoxy composites is examined in terms of its impact on Izod strength. This paper provides an extensive overview from fundamental studies on PETI-5 and xGnP, as well as applied studies on relevant composite materials.

• Carbon letters
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• v.19
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• pp.99-103
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• 2016

Porous carbons have attracted much attention for their novel application in gas storage. In this study, porous graphite nano-fiber (PGNFs)-based graphite nano fibers (GNFs) were prepared by KOH activation to act as adsorbents. The GNFs were activated with KOH by changing the GNF/KOH weight ratio from 0 through 5 at 900℃. The effects of the GNF/KOH weight ratios on the pore structures were also addressed with scanning electron microscope and N₂ adsorption/desorption measurements. We found that the activated GNFs exhibited a gradual increase of CO₂ adsorption capacity at CK-3 and then decreased to CK-5, as determined by CO₂ adsorption isotherms. CK-3 had the narrowest micropore size distribution (0.6–0.78 nm) among the treated GNFs. Therefore, KOH activation was not only a significant method for developing a suitable pore-size distribution for gas adsorption, but also increased CO₂ adsorption capacity as well. The study indicated that the sample prepared with a weight ratio of ‘3’ showed the best CO₂ adsorption capacity (70.8 mg/g) as determined by CO₂ adsorption isotherms at 298 K and 1 bar.

• 한국기계연구소 소보
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• s.18
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• pp.163-168
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• 1988

Impregnation of molten thermoplastic resin into continuous unidirectional fiber bundles was investigated. The degree of impregnation is defined as the ratio between the number of impregnated fibers and the total number of fibers of a bundle. The degree of impregnation was modeled as a function of time, impregnation pressure, temperature and tow size assuming the radial inward flow through the fiber bundle is governed by the Darcy's law. The permeability was assumed to be constant. Experiments were performed to evaluate the validity of the medel. Today's T300 graphite fiber bundles and Polyetheretherketone(PEEK) resin was used. A fiber bundle and resin powder were put into a mold and pressure and temperature were applied. After a predetermined time, the sample was taken out and microphotographs of the cross-section were taken. From the microphotographs, the number of impregnated fibers was counted and then the degree of impregnation was determined. Experiments were also performed for different tow sizes. Good agreements were found between the model and the experiments rendering a confidence in the model.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1996.04b
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• pp.13-19
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• 1996

The tribological properties of the aluminum short fiber and glass fiber reinforced tin-bronze matrix composites manufactured by vacuum hot pressing was studied. The effect of the composition and the relative density on the wear properties was examined by a reciprocal type tribo-test machine. The results were discussed by the observation of the microstructure of sintered specimen and worn surface observation using SEM and EDS. Addition of the fibers led to the wear resistance since the metal matrix was reinforced by the fibers. The reinforcement of the fiber seemed to be stronger as the distribution of the fibers was more uniform. Graphite also reduce the wear loss. The pores in the sintered composites seemed to play an important role to improve the wear resistance since the pores provide the places where the solid lubricants locate.