• 한국수소및신에너지학회논문집
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• 제21권5호
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• pp.398-404
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• 2010

Process conditions for MEA fabrications have significant effects on properties and performance of the MEAs for PEMFCs. In this study, effects of additives on the surface properties of the MEA was investigated to improve homogeneity of the coated catalyst layer. Another parameter that affects on characteristics of the MEAs is hot-pressing condition. Hot pressing condition was optimized by using DOE (design of experiment) method.

• 한국결정성장학회지
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• 제16권1호
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• pp.43-48
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• 2006

본 2부의 연구에서는 스파크 플라스마 소결의 온도분포, 상대밀도, 입자성장을 해석 하기 위하여 1부 연구의 시뮬레이션 이론을 바탕으로 스파크 플라스마 소결공정을 유한요소법(FEM)과 몬테카를로법(MCM)으로 전산모사하고 실험치와 비교한다. 전산모사를 통하여 소결체의 소결온도가 높을수록 입자성장이 커지고 밀도가 높아져 기계적 성질이 향상되고, 고상 소결에서 몬테카르로 단계가 증가할 수록 기공의 감소와 입자크기의 증대함을 보여 준다.

• 한국분말재료학회지
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• 제16권2호
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• pp.85-90
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• 2009

Magnesium and its alloys are attractive as light weight structural/functional materials for high performance application in automobile and electronics industries due to their superior physical properties. In order to obtain high quality products manufactured by the magnesium powders, it is important to control and understand the densification behavior of the powders. The effect of the sheath surrounding the magnesium powders on the plastic deformation and densification behavior during equal channel angular pressing was investigated in the study by experimental and the finite element methods. A modified version of Lee-Kim's plastic yield criterion, notably known as the critical relative density model, was applied to simulate the densification behavior of magnesium powders. In addition, a new approach that extracts the mechanical characteristics of both the powder and the matrix was developed. The model was implemented into the finite element method, with which powder compaction under equal channel angular pressing was simulated.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.747-753
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• 2000

There has been a number of investigations in recent years reporting the results obtained on the structure and properties of metals deformed to severe plastic deformation (SPD). Being deformed to SPD, ultra-fine grains (UFG) are usually formed, and UFG structure exhibits fundamental differences in original physical properties. One method often used to obtain SPD is equal channel angular pressing (ECAP). In order for this technique to be exploited, it is important to understand the deformation behavior during the ECAP processing and relationship to the configuration of die. The finite element method (FEM) has been used to investigate this issue. It has been found that the plastic deformation is sensitive to the channel angle and material properties and is not uniform across the width of the specimen and the pressing load is relative to deformation during the ECAP processing.

• 펄프종이기술
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• 제32권4호
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• pp.1-9
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• 2000

As the speed of the paper machine and printing press increases, the dependency of the production efficiency upon the frequency of web break increases. It is believed that flaw or crack that presents in paper is one of the most important for web break. Runnability of papers on the paper machine could be evaluated by measuring fracture toughness. In this paper the effect kof beating and pressing on the runnability was investigated using handsheets made from softwood bleached kraft pulp beaten to different freeness. Pressing pressure was also varied to obtain different levels of sheet consolidation. Density, tensile strength, and J-integral of the handsheets were evaluated. For measuring J-integral either a single specimen method or RPM method was employed. Results showed that the density and tensile strength were improved as beating and pressing increased because of increased interfiber bonding. J-integral increased with beating until the CSF reached 400mL. No significant difference in J-integral, however, was observed afterward with the increase of beating. And it appeared to be due to acceleration of the stress concentration around the crack that exists on the fiber wall of the sheet when cracks exists.

• Journal of the Korean Wood Science and Technology
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• 제29권4호
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• pp.33-39
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• 2001

포름알데히드와 요소의 몰비가 다른 2종류의 요소수지 접착제를 이용하여 접착제 첨가량과 열압시간 등 여러 조건에서 실험실 파티클보드를 열압하는 동안 배출되는 가스를 중류수에 용해 포집하고, 이렇게 얻어진 용액으로부터 포름알데히드 배출량을 미국 National Institute of Occupational Safety and Health (NIOSH) 3500의 방법에 의해 분석 비교하였다. 평가된 결과는 파티클보드를 열압하는 동안 배출되는 가스 중에서 포름알데히드량은 요소수지의 종류, 접착제 첨가량과 열압시간에 의해서 영향을 받는다는 것을 보여준다.

• 소성∙가공
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• 제15권7호
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• pp.524-528
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• 2006

Although equal channel angular pressing (ECAP), imposing large plastic shear strain deformation by moving a workpiece through two intersecting channels, is a promising severe plastic deformation method for grain refinement of metallic materials, its batch type characteristic makes ECAP inefficient for multiple-passing. Rotary-die ECAP (RDECAP) proposed by Nishida et al. can achieve high productivity by using continuous processing without taking out the samples from the channel. However, plastic deformation behavior during RD-ECAP has not been investigated. In this study, material plastic flow and strain hardening behavior of the workpiece during RD-ECAP was investigated using the finite element method. It was found that plastic deformation becomes inhomogeneous with the number of passes due to an end effect, which was not found seriously in ECAP. Especially, decreasing corner gap with increasing the number of passes was observed and explained by the strain hardening effect.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.1026-1029
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• 2002

Outlet of gas has been a big problem in deforming rubber or plastic in pressing mold. Air vent has been used to solve the problem, but it has weak points such as the increased cost, the increased number of process, and vent marks on the surface of a produce. In this study, the sintering method is used for making porous metal mold. Porous metal mold has many open pores, which are very small. When Porous metal mold is used for pressing mold, all process would be made short, produce cost would be down, and it would not leave vent marks on the surface of a produce. Porosity varies from sintering and pressing conditions, which are the pressure of compacting powder, the length of sintering time, sintering temperature and sintering atmosphere etc. This study will find optimized sintering temperature condition for the Porous metal mold.

• 한국정밀공학회지
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• 제19권8호
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• pp.187-193
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• 2002

Much research efforts have been made on the equal channel angular pressing (ECAP) which produces ultra-fine grains. Among many process parameters such as channel angles, frictions, die deformations and materials employed, the effects of material properties on the deformation behavior have been investigated. The finite element method has been used to investigate this issue.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.123-126
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• 2006

In this study, bottom-up type powder processing and top-down type SPD (severe plastic deformation) approaches were combined in order to achieve full density of carbon nanotube (CNT)/metal matrix composites with superior mechanical properties by improved particle bonding and least grain growth, which were considered as a bottle neck of the bottom-up method using the conventional powder metallurgy of compaction and sintering. ECAP (equal channel angular pressing), the most promising method in SPD, was used for the CNT/Cu powder consolidation. The powder ECAP processing with 1, 2, 4 and 8 route C passes was conducted at room temperature.