• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.23-26
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• 2005

In this work, effects of oxygen plasma on surfc1ce characteristics of carbon fibers were investigated in impact strength of carbon fibers-reinforced composites. The surface properties of the carbon fibers were determined by acid/base values, FT-IR, and X-ray photoelectron spectroscopy (XPS). Also, the mechanical properties of the composites were studied by impact strength measurements. As experimental results, the $O_{IS}/C_{IS}$ ratio of the carbon fiber surfaces treated by oxygen plasma was increased compared to that of untreated ones, possibly due to development of oxygen-containing functional groups. The mechanical properties of the composites, including impact strength had been improved by the oxygen plasma on fibers. These results could be explained that the oxygen plasma resulted in the increase of the adhesion of between fibers and matrix in a composite system.

• Current Industrial and Technological Trends in Aerospace
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• v.9 no.1
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• pp.139-149
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• 2011

The combustion chamber and nozzle of a liquid rocket engine need thermal protection against the high temperature combustion gas. The nozzle extension of a high-altitude engine also has to be compatible with high temperature environment and several kinds of cooling methods including gas film cooling, ablative cooling and radiative cooling are used. Especially for an upper-stage nozzle extension having a large expansion ratio, the weight impact on the launcher performance is crucial and it necessitated the development of light-weight refractory material. The present survey on the nozzle extension materials employed in the liquid rocket engines of USA, Russia and European Union has revealed a trend that the heavier metals like stainless steels and titanium alloys are being substituted with light weight carbon fiber or ceramic matrix composite materials.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.7
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• pp.98-104
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• 2022

Circular sawing and milling are general machining processes used for routing fiber-reinforced plastics (FRP). In this study, the productivity and cutting quality of a circular saw and flat endmill were compared. As a result, the productivity of the circular saw was approximately ten times higher than that of the endmill for the same tool life, and the burr size of the circular saw was 14 times smaller than that of the flat-end mill. The spectrogram analysis of the cutting sound also showed that the acoustic emission of the circular saw was more uniform than that of the flat end mill. Circular sawing is thus a more suitable process for the straight cutting of pultrusion FRP than a flat endmill.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.4
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• pp.344-350
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• 2004

This is the study on dry sliding wear behavior of unidirectional carbon fiber reinforced epoxy matrix composite at ambient temperature. The wear rates and friction coefficients against the stainless steel counterpart specularly processed were experimentally determined and the resulting wear mechanisms were microscopically observed. Three principal sliding directions relative to the dominant fiber orientation in the composite wear selected. When sliding took place against smooth and hard counterpart, the highest were resistance and the lowest friction coefficient were observed in the antiparallel direction. When the velocity between the composite and the counterpart went up, the wear rate increased. The fiber destruction and cracking caused fiber bending on the contact surface, which was discovered to be dominant wear mechanism.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.4
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• pp.337-343
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• 2004

This paper presents an experimental study of friction and wear properties of a unidirectional oriented continuous crbon-fiber reinforced epoxy composite at the ambient temperature. Friction and wear experiments were conducted in the three principal sliding direction of the fiber orientation in the composite were selected against the stainless steel counterpart specularly processed were using a pin -on-disc apparatus. Friction coefficient and specific wear rate at various normal loads and sliding velocities wear determined. When sliding took place against smooth and hard counterpart, the hightest were resistance and the lowest friction coefficient were observed in the anti-parallel direction. The wear track of the worn specimens was examined with a scanning electron microscope(SEM) to observe the damaged fibers on the surface. In addition, SEM observations of the worn surfaces allowed to identify the involved different wear mechanisms.

• Composites Research
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• v.29 no.4
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• pp.223-229
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• 2016

SiC nanoparticles were used to increase flexural properties of polymer matrix. This study was to manufacture huge concentration SiC nanoparticle/epoxy composites and to evaluate the dispersion. During mixing SiC nanoparticle and epoxy, 20 wt% SiC nanoparticle in total composites was used with both stirrer and sonication equipment together. Mixing speed and dispersion were improved with the method by using both stirrer and sonication equipment at the same time via mechanical test and FE-SEM. Based on the results, modeling of SiC nanoparticle dispersion could be established. Ultimately, unidirectional carbon fiber reinforced composites was manufactured using 20 wt% SiC nanoparticle/epoxy. Mechanical property of CFRP using dual stirrer and sonication mixing method was better than composites by single sonication mixing method.

• Composites Research
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• v.32 no.4
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• pp.177-184
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• 2019

If what the mechanical properties according to a layer have was found out by analyzing the already fabricated composite, it could be possible to develop the composite of the better performance than the existing products. In this study, we tried to calculate the mechanical properties of the inner prepreg lamina by applying the reverse design technique to the composite structure made by laminating prepregs. When the physical quantities obtained by the simple tensile test are used alone and the physical quantities obtained by the tensile test and the mode analysis are used at the same time, the results of this study show that the accuracy of the latter is higher Finally, the maximum error of $E_1$ predicted was 0.09% and the maximum error of predicted $E_2$ was 7%.

• Composites Research
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• v.31 no.6
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• pp.293-298
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• 2018

In this paper, we have studied the physical properties of braided composites for use as aircraft stringers. Process variables such as drum winder speed, braid velocity, and mandrel diameter for $30^{\circ}$, $45^{\circ}$ and $60^{\circ}$ braid preforms were quantified and different epoxy resin types were applied to the braided preform using TGDDM, YD-128. Physical properties such as tensile strength and flexural strength of braided composites were investigated. Thermal properties and decomposition temperature of epoxy resin were investigated by TGA analysis. As a result, the lower the angle of the braid composites, the higher the tensile strength and the Flexural strength. The physical properties of braided composites fabricated using TGDDM epoxy resin were superior to the physical properties of braided composites fabricated using YD-128 epoxy resin. This is because the molecular weight of TGDDM epoxy resin was higher than that of YD-128 epoxy resin.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.279-282
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• 2002

With the development of industrial society, the interest of new material is growing even in machining center. Composite materials in the new materials are superior to the metals In measure stability of strength, modulus and heat, moreover when mould is prepared, it can be done net shape manufacturing so it can be used widely in all sorts of machine parts, interior materials of car structural construct ions, the space aerial industry, ship materials, sports goods and so on. Therefore in this study, the property of processing drill on CFRP in composite materials by experimental study and some problems were examined.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.473-476
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• 2004

Carbon Fiber Reinforced Polymer(CFRP) composites are widely applied to strengthen deteriorated concrete structures. This paper presents the experimental results of the performance of reinforced concrete(RC) beams strengthened with Near Surface Mounted T-shape CFRP. Simple beams with 3m span length were tested to investigate the effect of CFRP reinforcement shapes on the flexural behavior of strengthened RC beams. The test results were analyzed with the special emphasis on the failure mode and the maximum load.