• 대한기계학회논문집A
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• 제23권6호
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• pp.1026-1038
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• 1999

Interlaminar fracture toughness of carbon/epoxy composite materials has been studied under tensile and flexural loading by the use of width tapered double cantilever beam(WTDCB) and end notched flexure(ENF) specimens. This study has significantly examined the effect of various interfacial ply orientation, ${\alpha}(0^{\circ},\;45^{\circ}\;and\;90^{\circ})$ and crack propagation direction, ${\theta}(0^{\circ},\;15^{\circ},\;30^{\circ}\;and\;45^{\circ})$ in terms of critical strain energy release rate through experiments. Twelve differently layered laminates were investigated. The data reduction for evaluating the fracture energy is based on compliance method and beam theory. Beam theory is used to analyze the effect of crack propagation direction. The geometry and lay-up sequence of specimens are considered various conditions such as skewness parameter, beam volume, and so on. The results show that the fiber bridging occurred due to the non-midplane crack propagation and causes the difference of fracture energy evaluated by both methods. For safer and more reliable composite structures, we obtain the optimal stacking sequence from initial fracture energy in each mode.

• 한국생산제조학회지
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• 제19권3호
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• pp.326-333
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• 2010

In this study, DAQ and TRA modules were applied to the CFRP single specimen testing method using AE. A method for crack identification in CFRP specimens based on k-mean clustering and wavelet transform analysis are presented. Mode I on DCB under vertical loading and mode II on 3-points ENF testing under share loading have been carried out, thereafter k-mean method for clustering AE data and wavelet transition method per amplitude have been applied to investigate characteristics of interfacial fracture in CFRP composite. It was found that the fracture mechanism of Carbon/Epoxy Composite to estimate of different type of fractures such as matrix(epoxy resin) cracking, delamination and fiber breakage same as AE amplitude distribution using a AE frequency analysis. In conclusion, the presented results provide a foundation for using wavelet analysis as efficient crack detection tool. The advantage of using wavelet analysis is that local features in a displacement response signal can be identified with a desired resolution, provided that the response signal to be analyzed picks up the perturbations caused by the presence of the crack.

• 한국철도학회논문집
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• 제8권6호
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• pp.573-580
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• 2005

Model I interlaminar fracture behaviors of the carbon/epoxy composite, one of the candidate composites for a tilting train carbody, were investigate by the use of DCB(Double cantilever beam) specimens. These specimens were made of CF3327 plain woven fabric with epoxy resin, and an artificial starter delamination was fabricated by inserting Teflon film with the thickness of $12.5{\mu}m$ of $25.0{\mu}m$ at the one end of the specimen. Mode I interlaminar fracture toughness was evaluated for the specimens with the different thickness of an inserter. Also delamination propagating behaviors and interlaminar fracture surface were examined through an ooptical travelling scope and a scanning electron microscope. We found that abruptly unstable crack propagation called as stick-slip phenomena was observed. In addition, interlaminar fracture behaviors were affected on the location and the morphology of a crack tip as well as an interface region.

• Composites Research
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• 제35권4호
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• pp.242-247
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• 2022

본 연구는 기존의 폐CFRP를 재활용하여 얻은 재생 탄소섬유를 다시 CFRP 제조에 활용하는 대신 탄소를 모재로 구성하는 탄소/탄소 (Carbon/Carbon, C/C) 복합소재를 제조하는 원료로 활용하기 위한 것이다. 먼저 일반적으로 많이 활용되는 에폭시수지 복합재료의 열분해 공정에 산화-불활성 분위기 변환 기술을 적용하여 1~2% 수준의 잔탄률을 19%까지 향상시켰으며, 이를 통해 에폭시수지 활용 C/C 복합재료 제조 가능성을 확인하였다. 다만, 산화-불활성 분위기 제어를 통한 열분해 공정으로 얻은 탄소의 경우 산소결합도가 높아 추후 개선 연구가 필요한 것으로 나타났다. 또한, 폐CFRP를 열분해 열처리 후 파쇄 및 해쇄 공정을 통해 단섬유 C/C 복합재료 시험편을 제조하였으며 이에 대한 기계적 물성 평가를 통해 최적 공정 조건을 도출하였다.

• Carbon letters
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• 제19권
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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.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.406-415
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• 2008

Recently, the amount of thermosetting plastic wastes have increased with the production of reinforced plastic composites and causes serious environmental problems. The epoxy composites, one of the versatile thermosetting plastics with excellent properties, cannot be melted down and remolded as what is done in the thermoplastic industry. In this research, a series of experiments that recovers carbon fibers from carbon fiber reinforced epoxy composites for train body was performed. We experimentally examined various decomposition processes and compared their decomposition efficiencies and mechanical property of recovered carbon fibers. For the prevention of tangle of recovered carbon fibers, each composites specimen was fixed with a Teflon supporter and no mechanical mixing was applied. Decomposition products were analyzed by scanning electron microscope (SEM), gas chromatography mass spectrometer (GC-MS), and universal testing machine (UTM). Carbon fibers could be completely recovered from decomposition process using nitric acid aqueous solution, liquid-phase thermal cracking and pyrolysis. The tensile strength losses of the recovered carbon fibers were less than 4%.

• Composites Research
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• 제17권6호
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• pp.1-7
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• 2004

입자강화복합재료에 관한 연구는 오래 전부터 수행되어왔다. 최근 활발한 연구가 이루어지고 있는 나노복합재료도 역시 입자강화복합재료의 한 종류라 할 수 있다. 본 연구에서는 섬유강화 복합재료의 모재로서 사용되어질 수 있는 다중벽탄소나노튜브/에폭시 복합재료를 제작하고 그 물성을 고찰하였다. 본 연구에서 정립한 제작 공정을 사용하여 제작 된 다중벽 탄소나노튜브/에폭시 복합재료의 인장 물성을 MWNT의 첨가량에 따라 고찰하였다 0.5wt%의 MWNT를 첨가 하였을 때, 인장강성은 19%, 인장강토에서는 12%의 증가를 보였다. 또한 경화시 발생하는 재응집 현상을 관찰하고, 기계적 물성을 더 높이 항상시키기 위해서는 이 현상을 억제해야 함을 확인하였다.

• Composites Research
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• 제17권3호
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• pp.38-44
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• 2004

레이다나 전자장비에서 복사되어 나오는 전자기파의 차폐는 상업적으로나 군사적으로 매우 중요한 문제이다. 본 연구에서는 다중벽 탄소나노튜브가 모재에 첨가된 섬유강화 복합재의 전자기적 특성을 고찰하기에 앞서, 다중벽 카본나노튜브와 모재로 이루어진 복합재료를 제작하고 그것에 대한 전자기적 특성을 고찰하였다. 복합재료의 제작 방법을 확립하였고, X-band (8.2GHz~12.4GHz)에서 첨가량과 공정변수에 따른 다중벽 탄소나노튜브/에폭시 복합재료의 유전율을 측정하였다. 또한 MWNT의 재응집 현상을 관찰하였고, 이것이 물성에 미치는 영향을 고찰하였다. 복합재료의 유전율은 MWNT의 분산도에 영향을 받았고, MWNT의 첨가량이 증가함에 따라 거의 선형적인 증가를 보였다.

• Composites Research
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• 제28권6호
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• pp.361-365
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• 2015

The influence of MWCNTs on fracture toughness properties of MWCNTs/Nickel-Pitch Fibers/epoxy composites (MWCNTs/Ni-PFs/epoxy) was investigated according to MWCNTs content. Nickel-Pitch-based carbon fibers (Ni-PFs) were prepared by electroless nickel-plating. The surface properties of Ni-PFs were determined by scanning electron microscopy (SEM) and X-ray photoelectron spectrometry (XPS). The fracture toughness of MWCNTs/Ni-PFs/epoxy was assessed by critical stress intensity factor ($K_{IC}$) and critical strain energy release rate ($G_{IC}$). From the results, it was found that the fracture toughness properties of MWCNTs/Ni-PFs/epoxy were enhanced with increasing MWCNTs content, whereas the value decreased above 5 wt.%. MWCNTs content. This was probably considered that the MWCNTs entangled with each other in epoxy due to an excess of MWCNTs.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 추계학술발표대회 논문집
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• pp.180-184
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• 2004

The tribological behavior of carbon epoxy composites whose surfaces have many small grooves of $100\mu m$ width was experimentally investigated with respect to the sliding direction against groove orientation, surface pressure (P) and velocity (V). The wear mechanism of the composites was observed to calculate the wear volume with respect to the friction coefficient using scanning electron microscopic (SEM). Experimental results show that the abrasive wear is dominant wear mechanism for the grooved composite surface and the friction and wear are greatly reduced when the sliding direction is parallel to the axis of groove because abrasive particles are removed through the grooves effectively.