• 비파괴검사학회지
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• 제36권1호
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• pp.9-17
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• 2016

The elastic modulus of a 3D-printed Kelvin foam plate is investigated by measuring the acoustic wave velocity of 1 MHz ultrasound. An isotropic tetrakaidecahedron foam with 3 mm unit cell is designed and printed layer upon layer to fabricate a Kelvin foam plate of 14 mm thickness with a 3D CAD/printer using ABS plastic. The Kelvin foam plate is completely filled with paraffin wax for impedance matching, so that the acoustic wave may propagate through the porous foam plate. The acoustic wave velocity of the foam plate is measured using the time-of-flight (TOF) method and is used to calculate the elastic modulus of the Kelvin foam plate based on acousto-elasticity. Finite element method (FEM) and micromechanics is applied to the Kelvin foam plate to calculate the theoretical elastic modulus using a non-isotropic tetrakaidecahedron model. The predicted elastic modulus of the Kelvin foam plate from FEM and micromechanics model is similar, which is only 3-4% of the bulk material. The experimental value of the elastic modulus from the ultrasonic method is approximately twice as that of the numerical and theoretical methods because of the flexural deformation of the cell edges neglected in the ultrasonic method.

• 한국분말재료학회지
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• 제27권1호
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• pp.37-43
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• 2020

The Fe-22wt.%Cr-6wt.%Al foams were fabricated via the powder alloying process in this study. The structural characteristics, microstructure, and mechanical properties of Fe-Cr-Al foams with different average pore sizes were investigated. Result of the structural analysis shows that the average pore sizes were measured as 474 ㎛ (450 foam) and 1220 ㎛ (1200 foam). Regardless of the pore size, Fe-Cr-Al foams had a Weaire-Phelan bubble structure, and α-ferrite was the major constituent phase. Tensile and compressive tests were conducted with an initial strain rate of 10^-3/s. Tensile yield strengths were 3.4 MPa (450 foam) and 1.4 MPa (1200 foam). Note that the total elongation of 1200 foam was higher than that of 450 foam. Furthermore, their compressive yield strengths were 2.5 MPa (450 foam) and 1.1 MPa (1200 foam), respectively. Different compressive deformation behaviors according to the pore sizes of the Fe-Cr-Al foams were characterized: strain hardening for the 450 foam and constant flow stress after a slight stress drop for the 1200 foam. The effect of structural characteristics on the mechanical properties was also discussed.

• 한국항공우주학회지
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• 제39권8호
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• pp.702-710
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• 2011

본 연구에서는 외부유동현상 해석에 오픈 소스 기반의 전산유체역학 프로그램인 OpenFOAM의 적용가능성을 검토하였다. 이를 위해 초음속, 천음속, 아음속 유동 영역에서 각 부분에 대표적인 해석 케이스를 선정하고 OepnFOAM에서 제공하는 해석자를 사용하여 해석을 수행했으며 해석 결과를 실험 결과 및 타 전산유체역학코드와 비교하였다. 충격파가 발생하는 초음속과 천음속 영역에서 충격파 예측의 정확도를 확인할 수 있었으며 경계 조건에 따른 결과의 정확도를 비교하였다. 아음속 유동 영역에서는 큰 박리가 일어나는 해석 케이스를 선정하여 복잡한 유동장하에서 OpenFOAM의 해석 정확도를 확인하였다. 위의 연구 결과를 바탕으로 OpenFOAM의 활용가능성과 한계를 확인하였고 이를 바탕으로 향후 OpenFOAM을 기반으로 수행할 연구 내용을 제시하였다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 추계학술발표대회
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• pp.17.2-17.2
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• 2009

Al Foam 소재는 다공질 금속으로써 저밀도 및 우수한 충격에너지 흡수능으로 최근 새로운 기능성 재료로 부상하여 세계 각국에서 연구개발이 활발하게 진행되고있다. 특히 이러한 Al Foam재를 자동차용 부품의 충격흡수재로사용할 경우 뛰어난 충격흡수능으로 인해 고안전 차량 부품 개발에 획기적인 기술 적용이 기대된다. 그러나, 종래 Al Foam재를 기계부품 등에 삽입할 경우 발포금속을 제조하여 부품 형상에 따라 가공하여 삽입하였으나 이는 공정 중 추가적인 기계 가공 및 비용이 들며 이에 따라생산성이 떨어지는 단점이 있었다. 따라서 본 연구논문에서는 차량용 충격흡수 부품 제작에있어 추가적인 가공 및 공정 수를 줄일 수 있는 Y-프로세스라는 주조공법을 적용하여 Net 형상 Al Foam재를 제작하였다. Y-프로세스는 Al Foam 금속 용탕이 주형에 투하되었을 때 Net 형상의 주형을 용탕 내 삽입하여 금속 용탕의 발포 및 응고시 Net 형상을따라 발포 및 응고가 되도록 하여 Net 형상의 Al Foam이삽입된 부품을 만드는 공법을 말한다. Y-프로세스로제조된 Al Foam재는 주형 내 완전히 충진되지는 못하였으나 주형내 충진된 Al Foam재의 상하부 셀크기가 비교적 균일한 모습을 나타내어 향후 공정제어를 통해 우수한 품질의 Net 형상 Al Foam 제조가 가능함을 알 수있었다.

• 한국항공우주학회지
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• 제40권9호
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• pp.781-788
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• 2012

공개소스 전산유체 해석 라이브러리인 OpenFOAM을 이용하여 액체 로켓 연소기의 산화제 매니폴드 내 유동 해석을 수행하였다. 정상 상태의 비압축성 난류 유동 해석을 통하여 분사기 차압 모사를 위한 다공성 매질 영역이 포함된 복잡한 3차원 형상에 대한 유동해석에 있어서의 OpenFOAM 적용 가능성을 평가하였다. 향후 로켓 연소장치 내의 주요 물리적 현상을 포함한 보다 다양한 해석 사례에 대한 평가를 수행함으로써 설계 평가 및 해석 도구로서의 OpenFOAM의 유용성 및 적용 범위를 확인/확대해나갈 계획이다.

• Fibers and Polymers
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• 제3권4호
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• pp.159-168
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• 2002

Polyurethane foams were produced by using a homogenizer as a mixing equipment. Effects of stirring speed on the foam structure were investigated with SEM observations. Variation of the bubble size, density of the foam, compressive strength, and thermal conductivity were studied. A hybrid foam consisting of polyurethane foam and commercial polystyrene foam is produced. Mechanical and thermal properties of the hybrid foam were compared with those of pure polyurethane foam. Advancement of flow front during mold filling was observed by using a digital camcorder. Four types of mold geometry were used for mold filling experiments. Flow during mold filling was analyzed by using a two-dimensional control volume finite element method. Variation of foam density with respect to time was experimentally measured. Creeping flow, uniform density, uniform conversion, and uniform temperature were assumed for the numerical simulation. It was assumed for the numerical analysis that the cavity has thin planar geometry and the viscosity is constant. The theoretical predictions were compared with the experimental results and showed good agreement.

• Steel and Composite Structures
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• 제25권3호
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• pp.327-335
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• 2017

To gain more knowledge of aluminum foam sandwich structure and promote the engineering application, aluminum foam sandwich consisting of 7050 matrix aluminum foam core and 304 stainless steel face-sheets was studied under three-point bending by WDW-T100 electronic universal tensile testing machine in this work. Results showed that when aluminum foam core was reinforced by 304 steel face-sheets, its load carrying capacity improved dramatically. The maximum load of AFS in three-point bending increased with the foam core density or face-sheet thickness monotonically. And also when foam core was reinforced by 304 steel panels, the energy absorption ability of foam came into play effectively. There was a clear plastic platform in the load-displacement curve of AFS in three-point bending. No crack of 304 steel happened in the present tests. Two collapse modes appeared, mode A comprised plastic hinge formation at the mid-span of the sandwich beam, with shear yielding of the core. Mode B consisted of plastic hinge formation both at mid-span and at the outer supports.

• 한국표면공학회지
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• 제28권2호
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• pp.83-91
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• 1995

A new method for preparation of thin nickel foam for Ni-MH battery was investigated. In this method, fine graphite powders of $1\mu\textrm{m}$～$2\mu\textrm{m}$ diameter were pasted into pores of thin polyurethane foam film in order to supply electric conducting seeds for nickel deposition by electroless plating reaction. After electroless plating, remaining polyurethane foam was removed chemically by organic solvent treatment and graphite particles also removed by ultrasonic cleaning. Porosity of formed nickel foam was about 85% During electroplating, porosity of the nickel foam decreased less than 5% up to $30\mu\textrm{m}$ coating thickness. And then it was electroplated and heat-treated to improve mechanical strength and ductility. Finally, thin nickel foam for Ni electrode of Ni-MH battery with 80% porosity and $350\mu\textrm{m}$～X$400\mu\textrm{m}$ thickness was obtained.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.680-683
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• 2004

This study is to obtain basic data concerned with properties of foam for foamed concrete and foaming method. Main factors of this study are types of foaming agents, temperature of solution with foaming agents, and types of foam generator. Testing items are size distribution of foam, foaming ratio to solution, and stability of foam. The results of this study were shown as follow. It is optimum condition of foam generator that length/diameter of foaming tube is 2.0, bead size within foaming tube is $4\~6mm$, and nozzle size of foaming tube is 10mm. AES and AOS are good results to produce high quality foam, and stability of foam is good in foaming temperature of $20^{\circ}C$.

• 한국자동차공학회논문집
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• 제15권2호
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• pp.41-49
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• 2007

More diversified and strengthened safety regulations require higher safety vehicle with less weight. The structural foam can play a role for restraining section distortion of main body members undergoing bending collapse at vehicle crash. In this study, using structural foam modeling technology, validated in previous work, the bending collapse characteristics were evaluated for two types of circular and actual vehicle body frame sections. With changing the foam filling method, outer panel thickness and section shape, load carrying capability and absorbed energy were observed. The results indicate valuable design strategy for effectively elevating bending collapse performance of body members with foam filled.