• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.833-841
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• 2013

In the case of composite material, a variety of characteristics were expressed depending on the materials that were composed of. In this study, the materials showing non-linear shear behavior were investigated among FRP composite. Each specimen was designed and analyzed according to ASTM D4255 method: regulations on the 2-rail. The dependent variables included in this experiment were a variety of fiber, fiber volume ratio, fiber array direction, temperature, material homogeneity. For determination of characteristics based on the fiber array, fiber array direction of 0, 30, 45, and 60 degrees were selected for test specimen. Temperature of 25, 40, 60, and $80^{\circ}C$ were considered for investigation of FRP materials'shear behavior based on the external temperature. Nonlinear shear behavior was observed throughout the FRP composite material in this study. Also, using vinyl ester resins, high fiber volume ratio, and fiber array direction of 45 degree appeared to show the most prominent nonlinear shear behavior. As for the findings related to the temperature change, non-linear behavior was decreased as the external temperature increased. For factory manufactured product, non-linear behavior was relatively at parity in comparison to the behavior found in the hand lay-up FRP composite specimen.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2000.11a
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• pp.63-63
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• 2000

저급의 고지 원료를 두께 방향으로 고온 압착을 가하여 건조함으로써 전반적인 종이 물성 을 향상시키는 콘디벨트 건조 방식은 70년대 중반부터 80년대에 이르는 10여년에 걸친 개발 과정을 거쳤으며 90년대에 들어서 핀랜드의 Inkeroinen에 위치한 V alemt- Tarnpella의 연구 소에 최초의 파일로트 설비가 설치되었으며 그 후 1996년에는 핀랜드 ENSO사의 P Pank밟oski 판지공장에 설치됨으로써 세계 최초의 상업생산설비를 이루게 되었다. 기존의 실린더 건조 기술과 비교할 때 콘디벨트 건조방식은 건조속도를 약 5-15배 향상시킬 수 있 으며, 건조 에너지 절감에 큰 효과가 있을 뿐만 아니라 기존의 실린더 건조시 종이가 폭방 향으로 수축되 어 인장 stiffness와 압축 강도 동의 종이 물성 이 저 하되 는 반면 습윤상태 의 섬유를 120도씨이상에서 가열에 의해 리그닌을 연화시킴과 동시에 섬유의 유연성을 증가시켜 준다. 그리고 높은 압력을 가해줌으로써 섬유간의 결합 면적을 증가시키고 건조시 종이의 폭방향의 수축을 감소시켜 인장강도, 내부결합강도, 밀도, 표면평활성, 투기저항성 등 종이의 물성을 대폭 향상시켜주는 혁신적인 제지기술로 인정받고 있으며 국내의 경우 현재 1998년 부터 상업생산을 이루어짐으로써 그 공헌도는 매우 크다고 할 수 있다. 골판지의 주원료가 되는 국산 골판지 고지 (Korean old corrugated container, K KOCC)의 거듭된 재생처리로 인하여 미세분의 함량이 전체 지료의 절반 이상에 달할 뿐만 아니라, 섬유가 각질화와 단섬유화로 인하여 고온압착 건조처리 만으로는 골판지 고지로 생 산된 원지의 강도를 버진펄프로 생산된 원지가 가지는 강도에 준하는 강도로 향상시키는데 한계점을 가지게 된다. 유럽의 제지선진국들은 골판지 원지의 강도를 향상시키는 방편으로 표변에 전분 사이즈 프레스 처리를 도입하였으며 본 연구에서는 고온 압착 건조 처리 설비를 활용한 전분 표면처리의 가능성을 검토하고 골판지 원지의 강도를 향상시키기 위한 표면처리조건을 탐색하였다.

• Composites Research
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• v.35 no.2
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• pp.106-114
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• 2022

Carbon fiber-reinforced plastic, well known high specific strength and high specific stiffness, have been widely used in the aircraft industry. Mostly the CFRP structure is fabricated by lamination of carbon fiber or carbon prepreg, which has major disadvantage called delamination. Delamination is usually produced due to absence of the through-thickness direction fiber. In this study, three-dimensional carbon preform woven in three directions is used for fabrication of aircraft wing unit structure, a part of repeated structure in aircraft wing. The unit structure include skin, stringer and rib were prepared by resin transfer molding method. After, the 3D structure was compared with laminate structure through compression test. The results show that 3D structure is not only effective to prevent delamination but improved the mechanical strength. Therefore, the 3d preform structure is expected to be used in various fields requiring delamination prevention, especially in the aircraft industry.

• Applied Chemistry for Engineering
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• v.18 no.6
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• pp.580-586
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• 2007

In this study, 4 directional carbon/carbon composites with different preform architectures were manufactured and their thermophysical properties are studied. Carbon fiber preforms are fabricated with fiber bundles using four different spaces. The density of the fabricated preforms were increased through pressure impregnation and carbonizing process. The increased density of the composites was graphitized at $2300^{\circ}C$. Microstructures of these composite were observed under scanning electron microscope. This was to understand the effect the preform architectures has on the thermophysical properties of carbon/carbon composites. Also, the behavior of thermal conduction and heat expansion was investigated and studied in association with the factors of the reinforced direction of fibers and unit cell of preforms.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.5
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• pp.323-330
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• 2023

The development of an analysis model that reflects the microstructure characteristics of polyvinyl alcohol (PVA) fiber-reinforced cementitious composites, which have a highly complex microstructure, enables synergy between efficient material design and real experiments. PVA fiber orientations are an important factor that influences the mechanical behavior of PVA fiber-reinforced cementitious composites. Owing to the difficulty in distinguishing the gray level value obtained from micro-CT images of PVA fibers from adjacent phases, fiber segmentation is time-consuming work. In this study, a micro-CT test with a voxel size of 0.65 ㎛³ was performed to investigate the three-dimensional distribution of fibers. To segment the fibers and generate training data, histogram, morphology, and gradient-based phase-segmentation methods were used. A U-net model was proposed to segment fibers from micro-CT images of PVA fiber-reinforced cementitious composites. Data augmentation was applied to increase the accuracy of the training, using a total of 1024 images as training data. The performance of the model was evaluated using accuracy, precision, recall, and F1 score. The trained model achieved a high fiber segmentation performance and efficiency, and the approach can be applied to other specimens as well.

• Textile Coloration and Finishing
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• v.8 no.5
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• pp.76-83
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• 1996

Fragrant microcapsules were prepared by in situ polymerization using urea-formaldehyde prepolymer. Lemon oil and migrin oil as susceptible materials were used. The diameter and distribution of the microcapsule were controlled by several factors, such as wall material, core material content, emulsion agent and stirring speed, respectively. Susceptible cotton fabrics with fragrant release functionality were successfully produced by using microcapsule containing fragrant materials.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.3
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• pp.237-245
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• 2003

Since the velocity is dependent on the fiber orientation in anisotropic composites, the application of traditional acoustic emission (AE) source location techniques based on the constant velocity to composite structures has been practically impossible. The anisotropy makes the source location procedure complicated and deteriorates the accuracy of the location. In this study, we have divided the region of interest(ROI) into a set of finite elements, taken each element as a virtual source, and calculated the arrival time differences between sensors by using the velocities at every degree from 0 to 90. The calculated and the experimentally measured values of the arrival time difference aye then compared to minimize the location error. The results from two different materials, namely AA6061-T6 and CFRP(uni-directional; UD, $[0]_{32}4$) laminate confirmed the practical usefulness of the proposed method.

• Composites Research
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• v.32 no.6
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• pp.403-407
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• 2019

Long-fiber-reinforced composites have the advantages of cost-competitiveness and high degree of freedom of molding compared to continuous-fiber-reinforced composites. On the other hand, it is difficult to ensure uniform characteristics due to the randomly distributed fiber orientation incurred from the process of manufacturing intermediate materials. In this study, the effect of the directionality of LFPS (Long Fiber Prepreg Sheet) materials on the mechanical properties was analyzed. The eddy current measurement method was used to analyze fiber orientations, and tensile and compression tests on LFPS materials were performed according to ASTM standards. In addition, the test results and theoretical values of LFPS materials were verified using the ROM (rule-of-mixtures) theory. These results confirmed the effect of fiber orientation on mechanical properties of discontinuous-fiber-reinforced composites.

• Bulletin of Korea Environmental Preservation Association
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• s.405
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• pp.9-11
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• 2013

화학물질은 현대문명에 필수적이다. 산업용 원료, 신소재, 섬유, 의약품, 농약 등 화학물질의 사용용도는 광범위하고 그 유용성은 무궁무진하다. 하지만, 언제부터인가 화학물질 유해성(有害性)이라는 용어에 익숙해지고 있다. 화학물질은 분해에 장시간이 소요되어 인체 또는 환경에 잔류하고 장기적으로는 각종 질병을 일으키기도 한다.

• The Korean Journal of Rheology
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• v.10 no.2
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• pp.82-91
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• 1998

액정고분자/폴리카보네이트 혼합계로 구성된 분자복합계를 쉬트상으로 가공할 때 취 약해지기 쉬운 횡단면 방향의 물성을 향상시키기 위하여 미세섬유상의 배향을 in-situ 상태 로 적절히 제어할수 있는 Simultaneous Convergent-Divergent(SCD) 다이를 설계·제작하 고 압출실험을 수행하여 얻은 압출 쉬트를 대상으로 구조-물성-가공의 상관관계를 조사하 였다. 액정고분자의 첨가 함량에 따른 토오크와 토출량의 변화는 액정고분자를 10wt% 소량 첨가하였음에도 현저한 감소 효과를 보였으며 약 30wt%일 때 최소로되었다. 이는 액정고분 자가 보강 기능외에 가공특성의 개선에도 큰 효과가 있어 가공조제로서의 가능성을 보이는 결과로 혼합계의 유변학적 특성 결과에서도 확인할수 있었다. 또 DSC와 DMA를 이용한 열 분석 결과 액정고분자의 함량이 증가함에 따라 PC의 유리전이온도가 다소 감소하는 현상을 보임에 미루어 이 혼합계는 부분적으로 상용성을 갖는 것으로 볼수 있으며 모폴로지 분석을 통해서도 이를 확인할수 있었다. TLCP/PC 혼합계로 구성되는 분자복합재를 SCD 다이를 사용하여 제조한 압출 쉬트의 방향성에 따른 기계적 물성은 기존의 쉬트 다이보다 흐름방향 으로는 다소 낮은 물성치를 보이지만 횡단면 방향으로는 물성이 현저히 향상됨을 관찰할수 있었다. 모폴로지 분석결과 기존의 쉬트 다이의 경우 벽면 부근에서는 액정고분자가 미세섬 유상으로 형성되어 흐름방향으로 배향되어 있지만 중심부에서는 액정 상태로 존재하는 반 면, SCD 다이의 경우 미세섬유상으로 형성된 액정고분자가 벽면에서부터 중심부로 갈수록 횡단면 방향으로 서서히 배향되어 있음을 확인할수 있었다.