• Carbon letters
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• 제14권1호
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• pp.58-61
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• 2013

In this work, the effect of catalysts on the mechanical properties of carbon fibers-reinforced epoxy matrix composites cured by cationic latent thermal catalysts, i.e., N-benzylpyrazinium hexafluoroantimonate (BPH) was studied. Differential scanning calorimetry was executed for thermal characterization of the epoxy matrix system. Mechanical interfacial properties of the composites were studied by interlaminar shear strength (ILSS), critical stress intensity factor ($K_{IC}$), and specific fracture energy ($G_{IC}$). As a result, the conversion of neat epoxy matrix cured by BPH was higher than that of one cured by diaminodiphenyl methane (DDM). The ILSS, $K_{IC}$, $G_{IC}$, and impact strength of the composites cured by BPH were also superior to those of the composites cured by DDM. This was probably the consequence of the effect of the substituted benzene group of BPH catalyst, resulting in an increase in the cross-link density and structural stability of the composites studied.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 추계학술발표대회 논문집
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• pp.158-162
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• 2001

The effects of chemical treatment on Kevlar-29 fibers have been studied in a composite system. The surface characteristics of the Kevlar-29 fibers were characterized by pH, acid-base value and X-ray photoelectron spectroscopy (XPS). The mechanical interfacial properties of final composites were studied by interlaminar shear strength (ILSS) and critical stress intensity factor ($K_{IC}$). Also, the impact properties of the composites were investigated in the differentiating studies between initiation and propagation energies, and ductile index (DI) along with maximum farce and total energy. It was found that the chemical treatment with phosphoric acid ($H_3PO_4$) solution significantly affected the degree of adhesion at interfaces between fibers and resin matrix, resulting in improving the mechanical interfacial strength of the composites. This was probably due to the presence of chemical polar groups on Kevlar surfaces, leading to an increment of interfacial binding force in a composite system.

• 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.

• Macromolecular Research
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• 제17권8호
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• pp.585-590
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• 2009

The cure behaviors, dielectric characteristics and fracture toughness of diglycidylether of bisphenol-A (DGEBA)/poly(ethylene terephthalate) (PET) blend system were investigated. The degree of conversion for the DGEBA/PET blend system was measured using Fourier transform infrared (FTIR) spectroscopy. The cure kinetics were investigated by measuring the cure activation energies ($E_a$) with dynamic differential scanning calorimetry (DSC). The dielectric characteristic was examined by dielectric analysis (DEA). The mechanical properties were investigated by measuring the critical stress intensity factor ($K_{IC}$), critical strain energy release rate ($G_{IC}$), and impact strength test. As a result, DGEBAIPET was successfully blended. The Ea of the blend system was increased with increasing PET content to a maximum at 10 phr PET. The dielectric constant was decreased with increasing PET content. The mechanical properties of the blend system were also superior to those of the neat DGEBA. These results were attributed to the increased cross-linking density of the blend system, resulting from the interaction between the epoxy group of DGEBA and the carboxyl group of PET.

• 공업화학
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• 제23권3호
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• pp.313-319
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• 2012

본 연구에서는 Polyacrylonitrile (PAN)계 탄소섬유 표면에 구리도금 표면처리가 탄소섬유 강화 복합재료의 기계적 계면 특성에 미치는 영향에 관하여 관찰하였다. 탄소섬유 표면특성은 주사전자현미경, X-선 광전자 분광법, X-선 회절분석기, 접촉각 측정기로 측정하였고, 탄소섬유 강화 복합재료의 기계적 계면 물성은 층간전단강도(interlaminar shear strength, ILSS)와 파괴인성(critical stress intensity factor, $K_{IC}$)측정을 통하여 알아보았다. 실험결과로부터, 기계적 계면물성은 탄소섬유 표면에 COOH group과 도금된 구리함량이 증가됨에 따라 순차적으로 증가되는 것이 확인되었으나, 도금시간을 길게 하여 과량의 구리가 도입되었을 경우 기계적 계면 물성을 도리어 감소시키는 것으로 확인되었다. 결론적으로 구리함량이 탄소섬유 복합재료의 기계적 계면물성을 결정하는 중요 요소라 판단되나, 최적의 함량이상에서는 계면분리에 의한 물성저하의 원인이 될 수 있다.

• Journal of the Korean Wood Science and Technology
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• 제39권5호
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• pp.451-458
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• 2011

Adhesives derived from renewable resources allow wood panel producers to make lower cost alternatives to formaldehyde-based adhesive resins. Among them, adhesive components extracted from industrial by-products or wastes are the most important research fields in the efficient utilization of waste and cost reduction. In our study, the rapeseed flour, which is a by product from the production of biodiesel extracted from rapeseed, was introduced to develop alternative adhesives for the production of wood flooring. The rapeseed flour was hydrolyzed with 1% sodium hydroxide solution and PF prepolymers were prepared with 3-molar ratios, 1.8, 2.1 and 2.4. The linear fracture mechanics was introduced to evaluate the glue bond quality in wood flooring composed of fancy-veneered and plywood, and the formaldehyde emission and adhesive penetration were also investigated. The formaldehyde emissions of wood flooring met the requirement of the standard of $SE_0$ specified in the KS standard. The rapeseed flour adhesive penetrated sufficiently into the vessel elements and lumens in fancy veneer and plywood and gave strong bond quality to the wood flooring. The fracture mechanics was introduced to evaluate the adhesive joint between fancy veneer and plywood. The critical stress intensity factor ($K_{IC}$) of boliva overlayed wood flooring was increased with increasing molar ratio and this was the same tendency in oak overlayed wood flooring. From the results, the formulated adhesives were efficiently used to bond fancy veneer onto the plywood to make wood flooring and showed a potential to be used as a component of environmentally friendly adhesive resin systems for production of flooring.

• 폴리머
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• 제24권2호
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• pp.245-251
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• 2000

에폭시 (EP) 수지와 폴리우레탄(PU) 으로 제조된 블렌드 시스템의 접촉각과 기계적 특성을 연구하였다. EP의 경화제로 20 phr의 DDM (4,4'-diamino diphenyl methane)이 사용되었으며 EP/PU의 함량은 100/0~100/60까지 변화시켰다. 접촉각은 Rame-Hart goniometer를 사용 하였으며 젖음액으로는 증류수와 diiodomethane을 사용하였다. 본 연구에서는 geometric 방법을 사용한 Owens-Wendt와 Wu's model이 블렌드 시스템의 표면 자유에너지를 알아보는데 사용되었다. 시편의 기계적 성질과 강인성은 임계 응력 세기 인자(critical stress intensity factor, $K_{IC}$)와 충격 강도 시험을 통하여 알아보았다. 그리고 특히 충격 강도는 상온과 극저온에서 알아보았다. 그 결과로서, 블렌드 시스템에 있어서 표면 자유에너지의 극성 요소는 저온에서 충격 강도를 증가시키는 PU의 함량에 크게 영향을 주었음을 알 수 있었다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.273-275
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• 2002

In this studies, curing behavior and mechanical properties of tetrafunctional epoxy resin (4EP)/ fluorine-containing epoxy resin (FEP) blend systems was investigated with 4, 4'-diaminodiphenol methane (DDM) as a curing agent. The cure activation energies $(E_a)$) were studied by Flynn-Wall-Ozawa's equation with dynamic DSC method. For the fracture toughness of the casting specimens, the critical stress intensity factor ($K_{IC}$) and the specific fracture energy ($G_{IC}$) were determined by fracture toughness test.

• Elastomers and Composites
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• 제39권1호
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• pp.42-50
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• 2004

본 연구는 열잠재성 개시제인 N-benzylpyrazinium hexafluoroantimonate (BPH)로 개시되어진 이관능성 에폭시인 diglycidylether of bisphenol A (DGEBA)와 변성 polyurethane (PU) 블렌드의 PU의 함량에 따른 경화거동과 파괴인성을 연구하였다. 블렌드의 경화거동은 시차주사 열량계(DSC)와 near-IR 을 통해 관찰하였고, 파괴인성은 임계응력 세기인자($K_{IC}$)와 임계 변형에너지 방출속도($G_{IC}$)를 측정하였다. 실험 결과, 경화 활성화에너지($E_a$)와 전환율(${\alpha}$)은 PU의 함량이 10 phr에서 최고값을 나타냈으며, $K_{IC}$는 전환율과 유사한 경향을 나타냄을 확인하였다. 이는 PU의 이소시아네이트기와 DGEBA의 하이드록실기 사이의 수소 결합이 증가함에 따라 블렌드의 가교밀도가 증가했기 때문으로 판단되어 진다.

• Journal of Mechanical Science and Technology
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• 제19권11호
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• pp.1988-1997
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• 2005

This study is concerned with structural integrity evaluations for the interference-fit flywheels in reactor coolant pumps (RCPs) of nuclear power plants. Stresses in the flywheel due to the shrinkage loads and centrifugal loads at the RCP normal operation speed, design overspeed and joint-release speed are obtained using the finite element method (FEM), where release of the deformation-controlled stresses as a result of structural interactions during rotation is considered. Fracture mechanics evaluations for a series of cracks assumed to exist in the flywheel are conducted, considering ductile (fatigue) and non-ductile fracture, and stress intensity factors are obtained for the cracks using the finite element alternating method (FEAM). From analysis results, it is found that fatigue crack growth rates calculated are negligible for smaller cracks. Meanwhile, the material resistance to non-ductile fracture in terms of the critical stress intensity factor (K$_{IC}$) and the nil-ductility transition reference temperature (RT$_{NDT}$) are governing factors for larger cracks.