• Journal of the Korean Ceramic Society
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• v.42 no.8 s.279
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• pp.593-598
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• 2005

Polycarbosilane was synthesized by the Kumada rearrangement of polydimethylsilane in the presence of zeolite (ZSM-5) as a catalyst at $350^{\circ}C$. The prepared polycarbosilane had very low molecular weight ($M_w=500$), so that it was not suitable to fabricate SiC fiber by melt spinning. Further polymerization of PCS was conducted around $400^{\circ}C$ to obtain spinnable polycarbosilane. After polymerization, the polycarbosilanes were isolated by distillation according to the molecular weight distributions. The PCS with a controlled molecular weight distribution was spun into continuous polycarbosilane green fibers. The PCS green fiber was successfully transformed into silicon oxycarbide fiber. The room temperature strength of the SiC fiber was around 1.5 - 1.8 GPa. The oxidation behavior and the tensile strength after oxidation were also evaluated.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.1
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• pp.30-36
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• 2005

This study is to investigate a damage estimation of single edge notched tensile specimens as a function of acoustic emission(AE) according to the uni-directionally oriented carbon fiber/epoxy composites, CFRP In fiber reinforced composite materials, AE signals due to several types of failure mechanisms are typically observed. These are due to fiber breakage, fiber pull-out matrix cracking, delamination, and splitting or fiber bundle breaking. And these are usually discriminated on the basis of amplitude distribution, event counts, and energy related parameters. In this case, AE signals were analyzed and classified 3 regions by AE event counts, energy and amplitude for corresponding applied load. Bath-tub curve shows 3 distinct periods during the lifetime of a single-edge-notch(SEN) specimen. The characterization of AE generated from CFRP during SEN tensile test is becoming an useful tool f3r the prediction of damage failure or/and failure mode analysis.

• Carbon letters
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• v.9 no.4
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• pp.316-323
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• 2008

The factors that influence ablation resistance in fiber composites are properties of the reinforced fiber and matrix, plugging quantity of fiber, geometrical arrangement, crack, pore size, and their distributions. To examine ablation resistance according to distribution of crack and pore size that exist in carbon/carbon composites, this study produced various sizes of unit cells of preforms. They were densified using high pressure impregnation and carbonization process. Reinforced fiber is PAN based carbon fiber and composites were heat-treated up to $2800^{\circ}C$. The finally acquired density of carbon/carbon composites reached more than $1.932\;g/cm^3$. The ablation test was performed by a solid propellant rocket engine. The erosion rate of samples is below 0.0286 mm/s. In conclusion, in terms of ablation properties, the higher degree of graphitization is, the more fibers that are arranged vertically to the direction of combustion flame are, and the less interface between reinforced fiber bundle and matrix is, the better ablation resistance is shown.

• 한국연소학회:학술대회논문집
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• 2006.04a
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• pp.19-25
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• 2006

Energy efficient and low pollution combustion systems the use gaseous fuels have been in great demand in recent year. Radiant burner in many different forms are emerging as very desirable combustion systems for same reason. Porous radiant burners are used in drying, preheating and curing, and in other type of materials processing and manufacturing processes. However, little knowledge is available about the operating characteristics and the structure of flames in porous ceramic fiber radiant burners. The objective of the present work is to investigate the global performance characteristics of the ceramic fiber burner. A detailed study which includes the spectral intensity, gas temperature, radiation efficiency and global pollutant emissions. Another objective is to study the flame structure of the ceramic fiber burner by measuring the local gas temperature. The results indicate that ceramic fiber burner do offer a 19-44% gain in radiant efficiency. The ceramic fiber burner exhibit significant spectral intensity peaks in the band at $2.0-2.5{\mu}m$. The local temperature distribution inside the mat and near the mat surface as a function of the equivalence ratio can be reasonably interpreted by the relation of the heat balance in the mat and movement of the reaction zone. Nox emission from ceramic fiber burner is less than 25ppm throughout the operating range.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.10a
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• pp.655-658
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• 2012

Optimal net residual dispersion (NRD) and distribution pattern of (SMF) length and residual dispersion per span (RDPS) in optical transmission links with artificial distribution of SMF length and RDPS required to flexibly design of optical links in dispersion management (DM) technique for compensating the distorted 960 Gbps optical signals due to interaction of group velocoty dispersion (GVD) and optical nonlinear effects are induced.

• Composites Research
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• v.33 no.1
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• pp.30-37
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• 2020

Stress distributions dependent on fiber arrangements are studied using the two-dimensional representative volume element (RVE) model for uni-directionally continuous fiber-reinforced composites subjected to transverse tensile loading. It is easily expected that the stresses around the fibers are concentrated mainly due to the stiffness mismatch between the fiber and matrix materials. In this presentation, it is shown that the stresses are not always increased although the distance between two fibers is shortened. The 2D RVE models, originally having a regular hexagonal fiber array, is utilized to study the effect of the fiber locations on the stress distributions. As the central fiber is relocated, the stress distributions around the fiber are obtained through finite element analysis. It is found that the stresses around the fiber are strongly dependent on the fiber distance as well as the angle between the loading direction and the line connecting two fibers.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.921-924
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• 2008

Several techniques, including transmission X-ray photography and AC-impedance spectroscopy, are available for evaluating the fiber dispersion in a fiber reinforced concrete Evaluating the fiber dispersion in fiber reinfored concrete needs since the fibers bridge crackseffectively. However, these equipment is very expensive. Therefore this paper presents the quantitative evaluation method based on the image analysis of sectional image taken using an ordinary digital camera. After detecting the fiber accurately, the fiber dispersion characteristics are represented by the coefficient such as the fiber dispersion coefficient, the number of fibers in unit area, and the distribution of the fiber orientation. Test were performed to evaluate the effectiveness of proposed method and the dispersion characteristics of fibers according placing method and flow direction. Additionally, the effect of fiber dispersion characteristics on mechanical properties was investigated. Test results shows that fiber aligned along the flow direction and more fibers placed and dispersion was better on the section parallel to the flow direction. And about 50% difference in the flexural tensile strength according to the placing method occured.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.12
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• pp.3277-3285
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• 1996

In this paper, w designed an opical power distribution device for application to an optical switching and an optical subscriber loop. We fabricated PSG thin film by LPCVD. Based on the measured index of fabricted thin film, rib-type waveguide was transformed to two-dimension by the effective index method and we simulated dispersion property to find asingle-mode condition. We found that the optimum design parameters of rib-type waveguide are:cladding layer of 3.mu.m, core layer of 3.mu.m, buffer layer of 10.mu.m, and core width of 4.mu.m. Each side of the guiding region was etched down to 4.mu.m to shape the core. We used these optimum parameters of the rib-type waveguide with branching angle of 0.5.deg. and simulted the Y-branch waveguide by the BPM simulation. Numerical loss in branching area was claculated to be 0.1581dB and equal to the total loss of the Y-branch. The loss of the fabricated Y-branch waveguide on PSG film ws 1.6dB at .lambda.=1.3.mu.m before annealing but was 1.2dB after annealing at 1000.deg. C for 10 minutes. Consequently, the loss of branching area from 3000.mu.m to 6000.mu.m in the z-direction was 0.8dB, and single-mode propagation was confirmed by measuring the near field pattern. For coupling the fabricated Y-branch waveguide with an optical fiber, we fabricated V-groove which was used as the upholder of optical fiber. An etching angle was 54.deg. and the width and depth of guiding groove was 150.mu.m, 70.mu.m, respectively. The optical fiber is inserted onto V-groove. Both the Y-branch and V-groove were connected through the index matching oil. Coupling loss after connecting Y-branch and the optical fiber on V-groove was 0.34dB and that after injecting index mateching oil was 0.14dB.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.38 no.3 s.116
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• pp.29-37
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• 2006

To use bamboo in the pulp industry, the anatomical characteristics of 60-day-old, 1-year-old, 2-year-old, and 3-year-old moso bamboo (Phyllostachys pubescens Mazel), and the characteristics of fiber and sheet of alkali pulp made of moso bamboo were investigated. Moso bamboo is composed of metaxylens and parenchyma cells in the inner part of the wall, and thick-walled small bundle sheathes near the outer walls. Moso bamboo showed the heterogeneity in anatomical structure. The longest fibers were shown in the middle part, and the widest width in the inner part. The lignin contents were 14.4% in 60-day-old bamboo, which was not lignified yet. The lignin contents in bamboo above 1 year were approximately 35%. The yields of alkali pulp of moso bamboo were in the range between 41 and 47%, and the yields tend to decrease with the increase of ages. The lignin contents of 60-day-old bamboo were 2.1% and those of bamboo above 1 year showed approximately 4% to 5% increment. The length, width, and curl index of fiber in alkali pulp appeared to be similar in all ages. However, coarseness increased slightly with the increase of bamboo ages. The distribution of long fiber was shown much in 60-year-old bamboo. The optical and mechanical properties of moso bamboo tended to decrease with the increase of bamboo age.

• Journal of the Korea Concrete Institute
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• v.20 no.6
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• pp.821-826
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• 2008

This study evaluated spalling and internal temperature distribution after elevated temperatures test for high strength concrete ($f_{ck}=60\;MPa$) column member with various polypropylene fiber volume fractions. The ISO-834 time-temperature curve was used for measurement of fire resistance properties. As the result of test, average internal temperature results indicated to low temperature in increased polypropylene fiber volume fraction. But, the highest internal temperature results show that does not difference in proportion of polypropylene fiber volume fractions.