• 한국세라믹학회지
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• 제30권12호
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• pp.993-998
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• 1993

Nicalon-fiber-reinforced SiC composites were fabricated via polymer solution infiltration/chemical vapor infiltration (PSI/CVI) and CVI. Specifically, data were taken and compared for flexural strength, fracture toughness, and processing time. The two process resulted in comparable mechanical properties, and PSI/CVI process resulted in significantly reduced infiltration time.

• 한국세라믹학회지
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• 제46권5호
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• pp.484-487
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• 2009

$SiC_f$/SiC composites with whiskers and pyrolytic carbon (PyC) coated whiskers in the matrix were fabricated for enhancement of the fracture behaviors by the whisker growing assisted chemical vapor infiltration (WA-CVI) process, respectively. $SiC_f$/SiC composites were also prepared by the conventional CVI process as reference material. The mechanical properties and fracture behaviors were analyzed by comparison of the two types of composites prepared by WA-CVI and conventional CVI. The densities of $SiC_f$/SiC composites were in the range of $2.6{\sim}2.65g/cm^3$. The flexural strengths of composite with whiskers and with those coated by PyC were 650 MPa and 600 MPa, respectively. The tensile strength of composites with whiskers was ${\sim}285$ MPa.

• 한국세라믹학회지
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• 제51권5호
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• pp.430-434
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• 2014

$SiC_f$/SiC composites were prepared using the hybrid process of chemical vapor infiltration (CVI) and polymer impregnation and pyrolysis (PIP). Before the application of PIP, partially matrix-filled preform composites with different densities were fabricated by control of chemical vapor infiltration time and temperature. The changes of the final density of the $SiC_f$/SiC composites had a tendency similar to that of preform composites partially filled by CVI. Composites with lower density after the CVI process had a larger increment of density during the PIP process. Three types of microstructures were observed on the fractured surface of the composite: 1) well pulled-out fibers and lower density, 2) slightly pulled-out fibers and higher density, and 3) only bulk SiC. The different fractions and distributions of the microstructures could have an effect on the mechanical properties of the composites. In this study, $SiC_f$/SiC composites prepared using a hybrid process of CVI and PIP had density values in the range of $1.05{\sim}1.44g/cm^3$, tensile strength values in the range of 76.4 ~ 130.7 MPa, and fracture toughness values in the range of $11.2{\sim}13.5MPa{\cdot}m^{1/2}$.

• Carbon letters
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• 제4권4호
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• pp.163-167
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• 2003

The "Film boiling" Chemical Vapor Infiltration (CVI) process is a rapid densification one developed in particular for the elaboration of carbon/carbon composite materials. In order to optimize this new thermal gradient process, we have carried out several studies, on one hand, about the nature of the complex chemical reactions in a confined medium, and on the other hand, relative to the role of heat and mass transfers inside the preform. We show in this study that the introduction of a permeable sheath around the preform leads to hybrid liquid/gas CVI process which presents the advantages of very high densification rates associated with a moderate input energy.

• 한국군사과학기술학회지
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• 제3권2호
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• pp.244-249
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• 2000

Thermal gradient chemical vapor infiltration (TG-CVI) process, which is one of the CVI techniques to densify a porous fiber preform, requires for a heater to have uniform surface temperature distribution. Thus, it is essential to design the shape of the heater and to predict the temperature distribution when the heater has a profile which is not a simple cylinder. In this study, an analytical method has been used to design the inner profile of a conical heater showing uniform temperature distribution, if its outer shape is specified. Temperature distribution on the heater surface has been calculated with the finite difference method and compared with the experimental results. When a heater had a combined profile with a large cone and a small cylinder, temperature was higher in the cylindrical part. To reduce the temperature difference between these areas, a hole-machining method has been proposed including other possible ones. A shape design and optimization program has been made to improve the temperature uniformity of the TG-CVI heater better than that designed with the analytical method.

• 대한감각통합치료학회지
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• 제16권1호
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• pp.35-44
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• 2018

목적 : 본 연구의 목적은 국내에 Miller Assessment for Preschoolers(MAP)을 사용하기 위해 필요한 번역, 역번역, 문항수정을 실시하고, 내용타당도를 검증하는 것이다. 연구방법 : 연구는 작업치료(학)과 교수, 번역가, 또는 작업치료사들을 대상으로 번역, 비교 통합 I, 역번역, 비교 통합 II, 이해도검증, 문항수정의 절차를 거쳤다. 자료 분석은 Microsoft office의 Excel을 이용하여 Content Validity Indices(CVI)를 구하였다. 결과 : 원본 MAP를 번역하여 교수 집단을 대상으로 내용타당도 검증시 평균 $3.66{\pm}0.40$점이었고 item-level CVI(I-CVI) 0.94, overal scale CVI(S-CVI) 0.83으로 나타났다. 원본 MAP과 영어로 역번역한 MAP의 내용타당도를 살펴본 결과는 평균 3.14점으로 나타났고 오류내용은 생략 13회, 용어오류 11회, 대체 6회, 순서오류 6회, 추가 3회로 나타났다. 치료사 9명을 대상으로 이해도 검증을 한 결과, 평균 $3.66{\pm}0.27$점이었고 I-CVI 0.93, S-CVI 0.58로 나타났다. 결론 : MAP의 국내 사용을 위하여 동시타당도, 구성타당도, 검사-재검사신뢰도, 검사자간신뢰도, 내적일치도 연구 등의 연구가 추가적으로 필요하다.

• 대한지역사회작업치료학회지
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• 제7권1호
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• pp.49-57
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• 2017

목적 : 본 연구의 목적은 노인의 지역사회 이동성을 측정하는 평가도구인 Life Space Assessment(LSA)를 한국어로 번역하여 이에 대한 적합성을 검증하기 위하여 내용 타당도와 이해도 검증을 실시하는 것이다. 연구방법 : 원문 LSA을 번역-역번역한 최종 한글 번역본을 6명의 전문가 위원에게 내용 타당도 검증을 실시하였고, 신입 작업치료사 13명에게 문항에 대한 이해도를 검증을 조사하였다. 내용 타당도와 이해도 검증은 내용 타당도 지수(Contents Validity Index; CVI)를 사용하였다. 결과 : 내용 타당도에 대한 각 문항에 대한 CVI .93~1.00이었으며, 도구 전체 CVI는 .99로 매우 높은 수준의 내용 타당도를 보였다. 또한 내용 이해도 결과는 각 문항 CVI .92~1.00로 분포하였고, 도구 전체 CVI는 .97로 매우 높은 수준으로 검증되었다. 결론 : LSA의 한국어 번역 검증 결과 내용 타당도 및 이해도가 매우 높은 수준으로 검증되어 국내에서 노인의 지역사회 이동성을 평가할 수 있는 도구로 적용가능성을 보여주었다. 앞으로의 연구에서는 LSA의 수렴타당도, 구성타당도, 신뢰도 검증 등의 다양한 연구들이 진행되어야할 것이다.

• 한국세라믹학회지
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• 제33권8호
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• pp.935-941
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• 1996

Two-dimensional carbon/carbon preforms made of PAN-based carbon yarn and phenolic resin were densified with pyrolysis of propane by pulse chemical vapor infiltration where repeated the cycle of gas introduction residence and evacuation. Maximim density increment was 14% when infiltration temperature and time were 100$0^{\circ}C$ and 21.25 hrs respectively. The distribution of deposits of pyrocarbon by this process has been occurred uniformly in the bottom middle and top of carbon/carbon composite preform Pulse CVI with residence is most effective in increasing density and shortening infiltration time among isothermal CVI and pulse CVI with and without residence.

• Journal of Mechanical Science and Technology
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• 제16권12호
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• pp.1652-1663
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• 2002

It is desirable to perform nondestructive evaluation to assess material properties and part homogeneity because manufacturing of carbon/carbon (C/C) composites requires complicated and costly processes. In this work several ultrasonic techniques were applied to carbon/carbon composites for the evaluation of spatial variations in material properties that are attributable to the manufacturing process. In a large carbon/carbon composite manufactured by chemical vapor infiltration (CVI) method, the spatial variation of ultrasonic velocity was measured and found to be consistent with the densification behavior in CVI process in order to increase the density of C/C composites. Ultrasonic velocity and attenuation depend on a density variation of materials. Low frequency through-transmission scans based on both amplitude and time-of-flight of the ultrasonic pulse were used for mapping out the material property inhomogeneity These results were compared with that obtained by dry-coupling ultrasonics. Pulse-echo C-scans was used to image near-surface material property anomalies such as the placement of spacers between disks during CVI. Also, optical micrograph had been examined on the surface of C/C composites using a destructive way.

• Carbon letters
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• 제25권
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• pp.25-32
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• 2018

In this study, a thermal-gradient chemical vapor infiltration (TG-CVI) process was numerically studied in order to enhance the deposition uniformity within the preform. The computational fluid dynamics technique was used to solve the governing equations for heat transfer and gas flow during the TG-CVI process for two- and three-dimensional (2-D and 3-D) models. The temperature profiles in the 2-D and 3-D models showed good agreement with each other and with the experimental results. The densification process was investigated in a 2-D axisymmetric model. Computation results showed the distribution of the SiC deposition rate within the preform. The results also showed that using two-zone heater gave better deposition uniformity.