• 신재생에너지
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• 제2권2호
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• pp.75-80
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• 2006

The effective thermal conductivities of $Mm(La_{0.6-0.8})Ni_{4.0}Co_{0.6}Mn_{0.2}Al_{0.2}$ [TL-492] with hydrogen and helium have been examined. Experiment results show that pressure has great influence on effective thermal conductivity in low pressure range [below 0.5 MPa]. And that influence decreases rapidly with increase of gas pressure. The reason is at low pressure, the mean free path of gas becomes greater than effective thickness of gas film which is important to the heat transfer mechanism in this research. And, carbon fibers have been used to try to enhance the poor thermal conductivity of TL-492. Three types of carbon fibers and three mass fractions have been examined and compared. Naturally, the highest effective thermal conductivity has been reached with carbon fiber which has highest thermal conductivity, and highest mass fraction. This method has acquired 4.33 times higher thermal conductivity than pure metal hydrides with quite low quantity of additives, only 0.99 wt% of carbon fiber. This is a good result comparing to other method which can reach higher effective thermal conductivity but needs much higher mass fraction of additives too.

• 대한건축학회논문집:구조계
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• 제34권2호
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• pp.49-56
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• 2018

The use of highly absorptive materials in cement-based materials is increasing for internal curing purpose. However, calculation of correct absorption capacity of such materials is not easy, which leads to change in the effective water-to-cement ratio of cement paste by either absorbing or releasing water. In this study, effective absorption capacity of a highly absorptive material was found using isothermal calorimetry. Moreover, the effect of specific surface area was investigated. It was found that the method was capable of finding effective water absorption capacity of activated carbon fiber. For the activated carbon fiber used in this research, the effect of specific surface area was negligible because the high BET surface area was due to micropores less than 1nm, which does not affect the rate of hydration curve. Thus, the effective absorption capacity of such materials can be found successfully using this method.

• 한국구조물진단유지관리공학회 논문집
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• 제6권2호
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• pp.225-231
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• 2002

Severe cracks on Reinforced Concrete (RC) structures caused by structural displacement can be often one of the main reasons for the degradation of tensile and flexural rigidities of RC structures and for the deterioration of durability and serviceability of RC structures through accelerated steel corrosion. These combined factors adversely affect the performance of RC concrete, leading to shortened life time of RC structures. In consideration of these problems, we conducted 3 point bending experiments by employing three different types of concrete specimens: fiber-net reinforced concrete (FNRC), polypropylene-fiber reinforced concrete (PFRC), and plain concrete (PC). FNRC is well known for its strong corrosion resistance, light self-weight, and excellent tensile strength, while PFRC is known to be effective in crack control. FNRC was found to have the best first and final crack resistances followed by PFRC and PC, as evidenced by the highest initial crack load and the smallest final crack width, respectively. The FNRC specimens with various tensile strength of fiber net exhibited greater ultimate strengths than those for PFRC and PC. Furthermore, the crack widths of FNRC specimens were smaller than those calculated by the crack-width estimation equation of the KCI and ACI code. Therefore, we conclude that fiber net reinforcement is effective not only on crack control, but also on loading share.

• Nuclear Engineering and Technology
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• 제47권7호
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• pp.884-894
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• 2015

Background: Fibers in concrete resist the growth of cracks and enhance the postcracking behavior of structures. The addition of fibers into a conventional reinforced concrete can improve the structural and functional performance of safety-related concrete structures in nuclear power plants. Methods: The influence of fibers on the ultimate internal pressure capacity of a prestressed concrete containment vessel (PCCV) was investigated through a comparison of the ultimate pressure capacities between conventional and fiber-reinforced PCCVs. Steel and polyamide fibers were used. The tension behaviors of conventional concrete and fiber-reinforced concrete specimens were investigated through uniaxial tension tests and their tension-stiffening models were obtained. Results: For a PCCV reinforced with 1% volume hooked-end steel fiber, the ultimate pressure capacity increased by approximately 12% in comparison with that for a conventional PCCV. For a PCCV reinforced with 1.5% volume polyamide fiber, an increase of approximately 3% was estimated for the ultimate pressure capacity. Conclusion: The ultimate pressure capacity can be greatly improved by introducing steel and polyamide fibers in a conventional reinforced concrete. Steel fibers are more effective at enhancing the containment performance of a PCCV than polyamide fibers. The fiber reinforcementwas shown to bemore effective at a high pressure loading and a lowprestress level.

• Current Optics and Photonics
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• 제7권1호
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• pp.47-53
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• 2023

We propose a centralized passive-optical-network monitoring scheme using the resonance-spectrum properties of a Fabry-Perot cavity based on fiber Bragg gratings. Each cavity consists of two identical uniform fiber Bragg gratings and a varying cavity length or grating length, which can produce a unique single-mode resonance spectrum for the drop-fiber link. The output spectral properties of each cavity can be easily adjusted by the cavity length or the grating length. The resonance spectrum for each cavity is calculated by the transfer-matrix method. To obtain the peak wavelength of the resonance spectrum more accurately, the effective cavity length is introduced. Each drop fiber with a specific resonance spectrum distinguishes between the peak wavelength or linewidth. We also investigate parameters such as reflectivity and bandwidth, which determine the basic performance of the fiber Bragg grating used, and thus the output-spectrum properties of the Fabry-Perot cavity. The feasibility of the proposed scheme is verified using the Optisystem software for a simplified 1 × 8 passive optical network. The proposed scheme provides a simple, effective solution for passive-optical-network monitoring, especially for a high-density network with small end-user distance difference.

• 콘크리트학회논문집
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• 제12권2호
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• pp.89-98
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• 2000

The mechanical properties of specialty cellulose fiber reinforced concrete and the contribution of specialty cellulose fiber to drying shrinkage crack reduction potential of concrete and theirs evaluation are presented in this paper. The effects of differing fiber volume fraction(0.03%, 0.06%, 0.08%, 0.1%, 0.15%, 0.2%) were studied. The results of tests of the specialty cellulose fiber reinforced concrete were compared with plain and polypropylene fiber reinforced concrete. Flexural performance(flexural strength and flexural toughness) test results indicated that specialty cellulose fiber reinforcement showed an ability to increase the flexural performance of normal- and high- strength concrete(as compared to plain and polypropylene fiber reinforced concrete). Optimum specialty cellulose fiber reinforced concrete were obtianed using 0.08% fiber volume fraction. Drying shrinkage cracking test results confirmed specialty cellulose fibers are effective in reducing the drying shrinkage cracking of normal and high-strength concrete(as compared to popylene fiber reinforced concrete).

• 한국건축시공학회지
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• 제17권4호
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• pp.321-329
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• 2017

콘크리트는 반취성 재료로서 우수한 압축력을 갖는 소재이나 인장력은 취약한 단점이 있다. 이러한 콘크리트의 단점을 개선하기 위한 섬유 보강 콘크리의 사용은 효과적인 인성강화에 대한 효과적인 방안이 될 수 있으며, 휨인성에 취약한 구조체에는 강섬유 보강 콘크리트를 사용함으로 성능을 개선하고 있다. 그러나 강섬유의 부식과 시공성 저하의 문제로 인해 대체 소재의 요구되고 있는 실정이다. 이에 본 연구에서는 확산성이 우수한 매크로 포타섬유를 사용한 콘크리트의 굳지 않은 콘크리트의 특성과 물리적 특성 및 건조수축 특성을 평가함으로 강섬유의 대체 가능성을 평가하고자 하였다. 실험 결과, 매크로 포타섬유는 강섬유 보강 콘크리트와 비교하였을 때 유동성 향상 및 역학적 성능이 우수한 것으로 나타났다. 매크로 포타 섬유를 사용한 콘크리트의 균열 저항성 부분에서도 강섬유 보강 콘크리트에 비하여 구조적인 균열과 건조 수축 저항성을 개선하는데 효과적인 것을 확인하였다.

• ETRI Journal
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• 제9권2호
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• pp.55-61
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• 1987

The effective cutoff wavelength of $LP_11$mode is measured as a function of fiber length for three types of single-mode optical fiber which have different characteristics in the index profile or the coating structure. The measured cutoff wavelength decreased linearly in a logarithmic scale of fiber length as increasing fiber length, and eventually became constant after 3km for two fiber types. It is found that the length dependence of cutoff wavelength is due to a mode coupling between the $LP_01$ and $LP_11$ modes.

• Current Optics and Photonics
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• 제2권6호
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• pp.525-531
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• 2018

The effect of eccentricity on dispersion and nonlinear properties of a photonic crystal fiber having elliptical air holes is investigated using a fully vectorial effective index method. It is found that the effective refractive index increases with increase of eccentricity. The dependence of dispersion and nonlinear properties of the PCF on the eccentricity of the air hole is investigated. It is revealed that eccentricity of the air hole affects the zero dispersion wavelength. Further, the nonlinear properties such as mode field area, nonlinear coefficient and self phase modulation of the Photonic crystal fibers are analyzed. The mode field area increases and the nonlinear coefficient decreases with increase in eccentricity. The variation of the self phase modulation with elliptical air hole is also discussed.

• Advanced Composite Materials
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• 제16권4호
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• pp.385-394
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• 2007

In this study, the effect of molding condition on the tensile properties for plain woven hemp fiber reinforced green composite was examined. The tensile properties of the composite were compared with those of the plain woven jute fiber composite fabricated by the same process. Emulsion type biodegradable resin or polypropylene sheet was used as matrix. The composites were processed by the compression molding where the molding temperature and its heating time were changed from 160 to $190^{\circ}C$ and from 15 to 25 min, respectively. The following results were obtained from the experiment. The tensile property of hemp fiber reinforced polypropylene is improved in comparison with polypropylene bulk. The strength of composite is about 2.6 times that of the resin bulk specimen. Hemp fiber is more effective than jute fiber as reinforcement for green composite from the viewpoint of strength. The molding temperature and time are suitable below $180^{\circ}C$ and 20 min for hemp fiber reinforced green composite. Hemp fiber green composite has a tendency to decrease its tensile strength when fiber content is over 50 wt%.