• Advanced Composite Materials
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• 제18권1호
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• pp.77-93
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• 2009

This paper investigated the damage transition mechanism between the fiber-breaking mode and the fiber-avoiding crack mode when the fiber-length is reduced in the unidirectional discontinuous carbon fiber-reinforced-plastics (CFRP) composites. The critical fiber-length for the transition is a key parameter for the manufacturing of flexible and high-strength CFRP composites with thermoset resin, because below this limit, we cannot take full advantage of the superior strength properties of fibers. For this discussion, we presented a numerical model for the microscopic damage and fracture of unidirectional discontinuous fiber-reinforced plastics. The model addressed the microscopic damage generated in these composites; the matrix crack with continuum damage mechanics model and the fiber breakage with the Weibull model for fiber strengths. With this numerical model, the damage transition behavior was discussed when the fiber length was varied. The comparison revealed that the length of discontinuous fibers in composites influences the formation and growth of the cluster of fiber-end damage, which causes the damage mode transition. Since the composite strength is significantly reduced below the critical fiber-length for the transition to fiber-avoiding crack mode, we should understand the damage mode transition appropriately with the analysis on the cluster growth of fiber-end damage.

• 한국해양공학회지
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• 제34권6호
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• pp.481-488
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• 2020

Composite materialsuch as glass-fiber reinforced plastic and carbon-fiber reinforced plastic (CFRP) shows anisotropic property and have been widely used for structural members and outfitings of ships. The structural safety of composite structures has been generally evaluated via finite element analysis. This paper presents a technique for updating the finite element model of anisotropic beams or plates via natural frequencies. The finite element model updates involved a compensation process of anisotropic material properties, such as the elastic and shear moduli of orthotropic structural members. The technique adopted was based on a discrete genetic algorithm, which is an optimization technique. The cost function was adopted to assess the optimization problem, which consisted of the calculated and referenced low-order natural frequencies for the target structure. The optimization process was implemented with MATLAB, which includes the finite element updates and the corresponding natural frequency calculations with MSC/NASTRAN. Material properties of a virtual cantilevered orthotropic beam were estimated to verify the presented method and the results obtained were compared with the reference values. Furthermore, the technique was applied to a cantilevered CFRP beam to successfully estimate the unknown material properties.

• Korean Chemical Engineering Research
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• 제56권6호
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• pp.798-803
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• 2018

Si을 리튬이온전지 음극활물질로 사용하기 위해 입도를 $0.5{\mu}m$ 보다 작은 크기로 제어하였고 표면에 탄소를 약 10 nm 두께로 코팅하였다. 그 위에 탄소섬유를 50~150 wt% 양으로 성장시키고 다시 한 번 탄소코팅을 진행하였다. 이렇게 만들어진 Si 합성물질은 전기전도성을 높이기 위한 공정으로 이종 금속을 혼합하였으며 수명 특성을 개선하기 위해 흑연과 복합화하였다. 실험 변수에 따른 재료들의 물리화학적 특성을 XRD, SEM 및 TEM을 사용하여 측정하였고 코인셀을 제조하여 전기화학적 특성을 평가하였다. Si/PC (Pyrolytic Carbon)/CNF (Carbon Nano Fiber)보다 Si/PC/CNF/PC가 전체적으로 Si 함량이 줄어 방전용량은 상대적으로 낮게 나타났지만 전지평가에서 중요한 수명특성에서는 좋은 결과를 보여주었다. 0.2 C rate에서 $1512mA\;h\;g^{-1}$의 초기 방전 용량과 78%의 초기 효율을 나타내었고 10 싸이클에서 94%의 용량 보존율을 보여주었다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 춘계학술대회 논문집
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• pp.85-91
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• 1996

The drilling experiment of carbon fiber epoxy composite material with WC-drill has been done under the various cutting condition in order to minimize the problems occured in the material when being drilled. It has been comfirmed by a frequencyanalysis of the cutting force signals that the variation of cutting force resulted from the periodic variation of the angle between the rotating drill and the stacking angle of the carbon fiber. The drilling experiment has been done with several drills having different point angles and the drilling characteristics, like the effects such that change in the point angle influences the cutting force and the external surface condition, was evaluated.

• 한국안전학회지
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• 제23권6호
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• pp.34-37
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• 2008

The composite materials are widely used in the many applications of industry as well as aerospace field because of their high specific stiffness and strength which benefits the material and provides potential energy savings. However, composite materials also have a low property about external applied impact. In this paper, impact tests were conducted on different sample types(glass, carbon and kevlar composite) to obtain information such as absorbed energy and composite deformation using an instrumented impact test machine (DYNATUP 8250). 3 type samples were compared to experimental results. The data from impact test provided valuable information between the different type samples by wet lay up. This paper shows results of that kevlar composite has larger absorption energy and deformation than others.

• Carbon letters
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• 제15권4호
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• pp.268-276
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• 2014

Recently, methods that usea carbon-based filler, a conductive nanomaterial, have been investigated to develop composite fillers containing dielectric materials. In this study, we added geometric changes to a carbon fiber, a typical carbon-based filler material, by differentiating the orientation angle and the number of plies of the fiber. We also studied the electrical and electromagnetic shield characteristics. Based on the orientation angle of $0^{\circ}$, the orientation angle of the carbon fiber was changed between 0, 15, 30, 45, and $90^{\circ}$, and 2, 4, and 6 plies were stacked for each orientation angle. The maximum effect was found when the orientation angle was $90^{\circ}$, which was perpendicular to the electromagnetic wave flow, as compared to $0^{\circ}$, in which case the electrical resistance was small. Therefore, it is verified that the orientation angle has more of an effect on the electromagnetic interference shield performance than the number of plies.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 추계학술발표대회 논문집
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• pp.63-66
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• 2003

The effect of punching density and material composition on the tensile properties and optimum condition of manufacturing of carbon needle punched perform was studies. The interlaminar tensile strength were increased but the intralaminar tensile strength were decreased with increasing punching density. In the case of the performs composed of continuous oxi-PAN fabrics, there was a considerable improvement of the interlaminar and intralaminar tensile strength.

• Composites Research
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• 제30권5호
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• pp.316-322
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• 2017

탄소섬유는 매우 우수한 기계적, 전기적, 열적 특성을 가진 소재로써, 고분자를 매트릭스로 하는 복합재료로써 산업적으로 널리 쓰이고 있다. 하지만 이 복합재료는 높은 강도 및 탄성을 가진 탄소섬유에 비해, 약한 고분자 매트릭스로 인한 분리 형상이 약점으로 지적되고 있다. 이를 해결하기 위해 강화재의 첨가가 필수적이다. 그래핀은 매우 우수한 기계적 물성을 지닌 강화재로써, 첨가 시에 높은 물성 향상을 기대할 수 있다. 하지만 그래핀 자체의 응집현상과 고분자 기지와의 약한 결합이 강화효과를 제대로 구현해내지 못하는 결과를 초래하고 있다. 이러한 문제점을 해결하기 위한 핵심 기술로 제시된 것이 기능기화 방법이며, 이를 통해 분산성을 향상시킬 수 있다. 본 연구에서는 멜라민을 이용하여 그래핀 나노플레이틀릿의 기능기화를 진행하고, 이를 에폭시 고분자 기지와 혼합하였다. 제조된 그래핀 나노플레이틀릿/에폭시을 이용하여 탄소섬유 강화 고분자 복합재료를 제조하고 굽힘 특성과 층간전단강도를 측정하였다. 그 결과 복합재료의 기계적 물성이 증가되었으며, 그래핀 나노플레이틀릿의 분산성이 향상됨을 확인하였다.

• 한국전기전자재료학회논문지
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• 제32권2호
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• pp.116-121
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• 2019

Hexagonal boron nitride particles (s-hBN) modified with 3-aminopropyl triethoxysilane (APTES) were used for the preparation of silicone composite materials. The microstructure of the composite materials was observed, and the thermal conduction and mechanical characteristics of the composite sheets were studied based on the compositions and microstructures. When a small amount of s-hBN particles was used, the thermal conductivity of the composite improved as a whole, and the tensile strength of the sheet also increased. The thermal conductivity and tensile strength of the composite in which a small amount of carbon fiber was added along with s-hBN were further improved. However, the use of carbon nanotubes with structural characteristics similar to those of carbon fiber resulted in lower thermal conductivity and tensile strength. Elastic silicone composites exhibiting 2.5 W/mK of thermal conductivity and a low hardness are expected to be used as thermally conductive interfacial sheet materials.

• 한국융합학회논문지
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• 제8권7호
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• pp.231-236
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• 2017

본 연구에서는 고분자재료인 CFRP(Carbon Fiber Reinforced Plastic)과 구조용 금속인 SM45C로 이루어진 이종 복합재료가 경량화 재료용으로 사용되고 있다. SM45C를 심재로 갖고 양면에 섬유 적층각도가 다른 단반향 CFRP를 접착시킨 샌드위치형 복합재료를 이용하여 CT(Compact Tension)시험을 기초로 한 유한요소 해석을 진행하였다. CT시험은 하중을 받는 재료내의 크랙으로 인한 파괴거동을 확인하기 위한 대표적인 방법이다. 이종 복합재료를 기계 구조물에 적용하기 위해서는 크랙 및 구멍에 대한 영향을 연구하여야 한다. 샌드위치형 복합재료의 CT시험에 의한 파괴거동을 시뮬레이션 해석으로 연구하였다. 본 연구 결과로서, [0/60/-60/0]의 적층각도를 가진 단방향 CFRP 샌드위치형태 복합재료가 우수한 강도를 갖으며 최대 등가응력은 약 182GPa정도가 나타났다. 또한 복합 재료 형상으로서의 디자인적 요소를 융합 기술에 접목함으로서 그 미적인 감각을 나타낼 수 있다.