• 소성∙가공
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• 제11권1호
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• pp.45-53
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• 2002

The forming process of metal matrix composites by die casting and squeeze casting process are limited in size and dimension In term of final parts. The melt strirring method have the problems that the homogeneous distribution of the reinforcements is difficult due to the low weldability and the density difference between the molten metal and the reinforcement. The thixoforming process for metal matrix composites has numerous advantages compacted to die casting, squeeze casting and compocasting. However, for the thixofoming process, the billet with the desired volume fraction must be heated to obtain a uniform temperature distribution over the entire cross-sectional areas. To obtain the reheating conditions of composites, the particulate reinforced metal matrix composites for thixoforming were fabricated by combined stirring process which is simultaneously performed with electro-magnetic stirring and mechanical stirring process. The matrix alloy and reinforcement are used to aluminum alloy(A357) and SiCp with diameter 14, $25{\mu}m$, respectively. The microstructure characteristics were investigated by changing the volume fraction and reinforcement size. The heating conditions to obtain the uniform temperature distribution in cross section area of fabricated metal matrix composites billet are proposed with heating time, the heating temperature and the holding time.

• 한국세라믹학회지
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• 제55권4호
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• pp.400-405
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• 2018

FCM nuclear fuel, a concept proposed as an accident tolerant fuel in light water reactors, consists of TRISO fuel particles embedded in a SiC matrix. The uniform dispersion of internal TRISO fuel particles in the FCM fuel is very important for improving the fuel efficiency. In this study, FCM sintered pellets with various volume ratios of TRISO-coated particles were prepared by hot press sintering. The distribution of TRISO-coated particles was quantitatively analyzed using X-ray ${\mu}CT$ and expressed as a dispersion uniformity index. TRISO-coated particles were most uniformly dispersed in the FCM pellets prepared using only overcoated TRISO particles without mixing of additional SiC matrix powder. FCM pellets with uniformly dispersed TRISO particle volume fraction of up to 50% were prepared using overcoated TRISO particles with varying thickness.

• 유통과학연구
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• 제20권9호
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• pp.73-81
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• 2022

Purpose: This study aimed to examine whether key audit matters (KAMs) readability influences investor reaction. Research design, data, and methodology: The signaling theory was applied to explain the behavior of investors when they receive useful information for their decisions. Data were collected from 1,866 firm-year observations from Thai listed companies in both the Stock Exchange of Thailand (SET) and the Market for Alternative Investment (MAI) for the fiscal years of 2016-2019. The study was based on secondary data, which were collected from the SET Market Analysis and Reporting Tool (SETSMART) database and the Stock Exchange of Thailand's website (www.set.or.th). A statistical regression method was used with panel data analysis to evaluate possible associations between KAMs readability and investor reaction. The study relied on popular readability measures (Fog Index). Moreover, investor reaction was measured by absolute cumulative abnormal return and abnormal trading volume. Results: It was found that the KAMs readability has positive significance on both absolute cumulative abnormal return and abnormal trading volume. Conclusion: This study showed a significant contribution to the implication of KAMs in an emerging economy. The results reveal that more readable KAMs disclosure distributed new insights and useful information to investors and led to reducing the information gap between auditors and investors.

• Composites Research
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• 제16권6호
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• pp.1-9
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• 2003

본 논문에서는 웨이블 분포 함수를 이용한 확률 파손 해석을 통해 복합재 압력 용기의 섬유 강도를 예측하였다. 그리고 섬유 강도의 크기 효과를 확인하고 해석의 타당성을 입증하기 위하여 섬유 인장 시편, 한 방향 복합재 시편과 복합재 압력 용기를 이용만 강도 시험이 수행되었다. 해석적 방법으로 웨이블 최약 링크 파손 모델과 다단계 연속 파손 모델을 이용하였고, 해석 결과를 상호 비교하였다. 크기 효과에 의해, 시편의 부피가 증가함에 따라 섬유 인장 강도가 감소하는 경향을 나타내었다. 해석을 통해 예측한 한 방향 복합재 시편과 복합재 압력 용기의 후프 층 섬유 강도 분포는 시험 값과 좋은 일치를 보였다. 섬유 강도의 크기 효과는 소재와 제작 공정 변수의 함수로서, 다른 소재 및 제작 공정에 대해서는 다른 크기 효과를 보이게 된다.

• Tribology and Lubricants
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• 제28권2호
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• pp.70-80
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• 2012

Non-contact type mechanical face seals installed in mechanical systems prevent leakage of working fluid using thin working fluid film between stator and rotor. For that purpose, various kinds of surface profiles, grooves and conings have been applied on seal surfaces of stator and rotor to generate hydrodynamic and hydrostatic pressure. The thickness distribution of working fluid film is one of important factors which affect the working performances of mechanical face seal, and it is strongly affected by the surface height profiles of stator and rotor. Therefore, appropriate design of surface height profiles of stator and rotor is necessary to optimize the working performances and life of mechanical face seal. In this study, numerical analysis using finite volume method was conducted to estimate the working performances of wavy mechanical face seals which have 36 coning combinations. As results, minimum thickness of working fluid film, leakage volume of working fluid and friction torque in static equilibrium condition of mechanical face seal, and stiffness of working fluid film were obtained. The results show that the working performances of mechanical face seal were affected by the coning combinations which can change the thickness distribution of working fluid film and pressure distribution in sealing region of mechanical face seal.

• Structural Engineering and Mechanics
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• 제78권2호
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• pp.117-124
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• 2021

This work focused on the novel numerical tool for the bending responses of carbon nanotube reinforced composites (CNTRC) beams. The higher order shear deformation beam theory (HSDT) is used to determine strain-displacement relationships. A new exponential function was introduced into the carbon nanotube (CNT) volume fraction equation to show the effect of the CNT distribution on the CNTRC beams through displacements and stresses. To determine the mechanical properties of CNTRCs, the rule of the mixture was employed by assuming that the single-walled carbon nanotubes (SWCNTs)are aligned and distributed in the matrix. The governing equations were derived by Hamilton's principle, and the mathematical models presented in this work are numerically provided to verify the accuracy of the present theory. The effects of aspect ratio (l/d), CNT volume fraction (Vcnt), and the order of exponent (n) on the displacement and stresses are presented and discussed in detail. Based on the analytical results. It turns out that the increase of the exponent degree (n) makes the X-beam stiffer and the exponential CNTs distribution plays an indispensable role to improve the mechanical properties of the CNTRC beams.

• 한국수소및신에너지학회논문집
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• 제34권3호
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• pp.283-291
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• 2023

The physical properties were analyzed for four gas diffusion layers, and gas diffusion electrodes (GDEs) for the cathode of high-temperature polymer electrolyte membrane fuel cell were fabricated through bar coating with three binder to carbon (B/C) ratios. Among them, The GDE from JNT30-A6P showed a significant change in secondary pore volume at a B/C ratio of 0.31, which had the largest pore volume among all GDEs. In the polarization curve, JNT30-A6P GDE showed the best membrane electrode assembly (MEA) performance with a peak power density of 384 mW/cm² at a a B/C ratio of 0.31. From the distribution of relaxation time analysis, the peak 1 corresponding to mass transfer resistance of oxygen reduction reaction (ORR) was significantly reduced in the JNT30-A6P GDE. This is the result that when the binder content decreased, the volume of the secondary pore increased, and the mass transfer resistance of ORR decreased, which played an essential role in the MEA performance.

• 해양환경안전학회지
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• 제23권1호
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• pp.83-90
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• 2017

본 연구는 해수유동모델을 이용하여 하계 한국 남해안 양식장 부근에서 수온의 시 공간적인 분포를 파악하였다. 한국 남해 조류의 흐름은 창조시 서향, 낙조시 동향하며, 쓰시마 난류의 흐름은 50 m보다 깊어지는 외양에서 연안에 비해 강하게 동북향 하였다. 조류, 바람, 쓰시마 난류 및 실시간 수온을 고려한 해수유동에서 하계 수온의 분포는 반폐쇄성 해역에서 $26{\sim}28^{\circ}C$로 높게 나타났으며, 외양으로 갈수록 낮아져 $18{\sim}22^{\circ}C$로 나타났다. 반폐쇄성 내만의 형태를 가지는 해역의 해수교환량을 계산한 결과 광양만 $10,331m^3/sec$, 여수-가막만 $16,935m^3/sec$, 그리고 거제-한산만은 $13,454m^3/sec$로 나타났다. 해수교환량이 적은 해역일수록 수온이 비교적 높게 나타난다.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2003년도 가을 학술논문집
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• pp.562-571
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• 2003

발전용원자로에서 뱃치방식으로 환경으로 배출된 액체유출물 내에 함유된 방사능 평가 결과에 오차를 유발하는 시료채취, 제조, 방사능 계측, 유출물 배출체적 측정 등 다양한 인자를 분석하였다. 환경배출 방사능 평가에 포함된 많은 인자들은 단일 측정에 의해 얻어지고 환경배출 방사능의 참값을 알 수 없음에 따라, 평가결과의 오차를 예측하는 것은 원칙적으로 불가능하다. 이에 따라 1993년 ISO가 권고한 측정의 불확도 표현지침에 근거하여 액체폐기물 배출방사능에 대한 불확도 평가모델을 수립하고 가상적인 조건에 대한 액체유출물 환경배출 방사능 평가결과의 불확도를 평가하였다. 그 결과, 액체유출물을 통한 환경배출 방사능 평가결과에 불확도를 유발하는 인자의 상대적인 기여도는 배출폐액의 체적, 시료의 체적, 총방사능 계측값의 순서를 갖는 것으로 나타났다. 또한 개별 변수의 확률분포와 특성값을 토대로 몬테칼로 모사법을 적용하여 최종 환경배출 방사능 평가결과의 확률분포를 해석함으로써, 지금까지 단일 값을 평가 및 보고되었던 발전용 원자로의 액체상 방사성물질 환경배출량이 실제로는 일정한 확률분포를 갖고 있음을 확인하였다.

• 대한화학회지
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• 제16권6호
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• pp.341-348
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• 1972

질소의 흡착 등온곡선을 이용하여 흡착체의 동공부피 분포를 계산하는 과정에서 표면장력의 곡률 의존도 고려 효과를 조사하였다. 즉, 장세헌 등에 의한 표면장력의 곡률 의존도식과 캘빈 식으로부터 주어진 압력에서의 캘빈반경을 구하고, 이것으로부터 흡착체의 동공부피 분포를 계산하였다. 이와 같이하여 얻은 계산 결과를 표면장력의 곡률 의존도를 고려하지 아니한 종래방법에 의한 계산 결과와 비교하였다. 일반적으로 곡률 의존도를 고려해주면 동공부피 분포 곡선의 극대부분이 큰 동공 쪽으로 이동한다. 또한 모세관 응축이 일어나는 상대압력이 종래까지 생각했던 것보다 훨씬 낮아지고 있다. 이러한 효과들은 흡착체의 동공들이 미세해 질수록 더욱 현저하게 일어난다.