• Steel and Composite Structures
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• 제28권6호
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• pp.671-679
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• 2018

The paper is devoted to the stability analysis of a simply supported five layer sandwich beam. The beam consists of five layers: two metal faces, the metal foam core and two binding layers between faces and the core. The main goal is to elaborate a mathematical and numerical model of this beam. The beam is subjected to an axial compression. The nonlinear hypothesis of deformation of the cross section of the beam is formulated. Based on the Hamilton's principle the system of four stability equations is obtained. This system is approximately solved. Applying the Bubnov-Galerkin's method gives an ordinary differential equation of motion. The equation is then numerically processed. The equilibrium paths for a static and dynamic load are derived and the influence of the binding layers is considered. The main goal of the paper is an analytical description including the influence of binding layers on stability, especially on critical load, static and dynamic paths. Analytical solutions, in particular mathematical model are verified numerically and the results are compared with those obtained in experiments.

• 정보저장시스템학회논문집
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• 제9권1호
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• pp.22-27
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• 2013

In this paper we are presenting a architecture of Co ion decorated graphene oxide as an electrode for supercapacitor application. Graphene oxide, which is exfoliated by oxidant from graphite, is the material for solving the problem of mass production and coating on the surface of working electrode. The $Co^{2+}$ ions are coated by using layer by layer(LBL) method on graphene oxide foam. The metal ion decorated graphene oxide shows enhanced capacitance performance when tested as supercapacitor electrode, showing the specific capacitance of $827Fg^{-1}$.

• Advances in aircraft and spacecraft science
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• 제6권4호
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• pp.273-282
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• 2019

This article is concerned with the investigation of geometrically non-linear vibration response of refined thick porous nanobeams. To this end, non-local theory of elasticity has been adopted to provide the nanobeam formulation. Voids or pores can affect the material characteristics of the nanobeam. So, their effects have been considered in this research and also there are various void distributions. The closed form solution of the non-linear problem has been used that is adopted from previous articles. Then, it is focused on the impacts of non-local field, void distribution, void amount and geometrical properties on non-linear vibrational characteristic of a nano-size beam.

• Journal of Electrochemical Science and Technology
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• 제9권3호
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• pp.229-237
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• 2018

The electrochemical sensing performance of metal-graphene hybrid based sensor may be significantly decreased due to the dissolution and aggregation of metal catalyst during operation. For the first time, we developed a novel large-area high quality three dimensional graphene foam-incorporated gold nanoparticles (3D-GF@Au) via chemical vapor deposition method and employed as free-standing electrocatalysis for non-enzymatic electrochemical glucose detection. 3D-GF@Au based sensor is capable to detect glucose with a wide linear detection range of $2.5{\mu}M$ to 11.6 mM, remarkable low detection limit of $1{\mu}M$, high selectivity, and good stability. This was resulted from enhanced electrochemical active sites and charge transfer possibility due to the stable and uniform distribution of Au NPs along with the enhanced interactions between Au and GF. The obtained results indicated that 3D-GF@Au hybrid can be expected as a high quality candidate for non-enzymatic glucose sensor application.

• 한국분말재료학회지
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• 제25권5호
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• pp.415-419
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• 2018

Porous metals demonstrate not only excessively low densities, but also novel physical, thermal, mechanical, electrical, and acoustic properties. Thus, porous metals exhibit exceptional performance, which are useful for diesel particulate filters, heat exchangers, and noise absorbers. In this study, SUS316L foam with 90% porosity and $3,000{\mu}m$ pore size is successfully manufactured using the electrostatic powder coating (ESPC) process. The mean size of SUS316L powders is approximately $12.33{\mu}m$. The pore properties are evaluated using SEM and Archimedes. As the quantity of powder coating increases, pore size decreases from 2,881 to $1,356{\mu}m$. Moreover, the strut thickness and apparent density increase from 423.7 to $898.3{\mu}m$ and from 0.278 to $0.840g/cm^3$, respectively. It demonstrates that pore properties of SUS316L powder porous metal are controllable by template type and quantity of powder coating.

• 폴리머
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• 제27권4호
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• pp.340-348
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• 2003

변형된 Stud-pull 시험 방법을 통해 탄소강 기재 위에 발포된 폴리우레탄의 접착 강도를 측정하였다. 아연인산으로 처리한 표면이 거친 탄소강 위에서 발포시킨 폴리우레탄의 접착 강도는 0.95 kN으로서 표면이 매끈한 양극산화된 탄소강 위에서 발포된 폴리우레탄의 접착 강도인 0.38 kN 보다 높게 나타남으로서 그 타당성이 입증되었다. 이 시험법을 여러 온도로 미리 가열된 탄소강 기재 위에서 폴리우레탄을 발포 접합시킨 시료들에 적용한 결과, 6$0^{\circ}C$ 이상으로 미리 가열된 금속 기재 위에서 발포된 폴리우레탄은 높은 접착 강도를 나타내었다. 또한 위의 시료를 수증기를 흡착하는 용기에 노출시켜 접착 강도를 측정하였는데 4$0^{\circ}C$ 보다 낮거나 7$0^{\circ}C$의 높은 온도로 유지된 금속 기재 위에서 발포된 폴리우레탄의 접착 강도는 많이 감소하였다. HCFC-141b와 HFC-245fa로 발포된 폴리우레탄의 접착력을 비교하였는데 HFC-245fa로 발포된 시료의 접착력이 0.03 kN 만큼 낮았으며 두 시료를 수증기에 노출시 HFC-245fa로 발포된 시료는 계면 근처에 존재하는 가스로 채워진 빈공간 영역의 적은 면적 비율로 인해 접착력이 거의 그대로 유지되었다. 이런 현상들은 기재의 온도, 기재의 표면 처리 방법, 발포제의 종류에 따라 금속 기재와 고분자와의 계면 근처에서의 미세조직학적인 차이에 의한 결과로 판단된다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.190-195
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• 2004

The compression-compression fatigue properties of the closed cell Al-Si-Ca alloy foams have been studied. The monotonic and cyclic compressive properties were compared with each other and the fatigue stress-life (S-N) curves were presented. In compression-compression fatigue, the crushing was found to initiate in a single band which broadens gradually with additional fatigue cycles. Progressive shortening of the specimen took place due to a combination of low cycle fatigue failure and cyclic ratcheting which is in accordance with the findings of previous researchers [1-3]. Young's modulus of the foam was found to decrease with the increasing strain in case of fatigue test however in case of monotonic compression test the value of Young's modulus increased with the strain (number of cycles). The endurance limit on the basis of $10^{7}$ cycles obtained by extrapolating the experimental results were 0.98 MPa and 1.70 MPa for load ratios 0.1 and 0.5 respectively which are 34 % and 59 % of the plateau stress.

• 한국주조공학회지
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• 제25권5호
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• pp.203-208
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• 2005

The main emphasis of this study is to optimize the process variables for manufacturing aluminum foam materials by direct foaming of remelted aluminum scraps. Aluminum foams were fabricated from two different raw materials, pure aluminum and used beverage cans. For both cases, $TiH_{2}$ was used as a foaming agent. Calcium was added as a thickener for the foaming of pure aluminum and no thickener was added for that of used beverage Cans because the pre-existing oxides of the used beverage cans are used as a thickener. Calcium and $TiH_{2}$ content varies from 0.5wt.% to 2.0wt.% and from 0.5wt.% to 1.5wt.%, respectively. The processing conditions, such as the effect of calcium on the melt viscosity, foaming temperature, and the optimum amount of the foaming agent with regard to the melt viscosity were discussed.

• 한국통신학회논문지
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• 제26권11B호
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• pp.1620-1627
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• 2001

본 논문에서는 PCS와 IMT-2000 서비스를 동시에 수용할 수 있는 광대역 안테나를 설계하였다. 광대역 특성을 얻기 위하여 두 개의 폼 물질, 기생소자로 구성된 개구면 결합 방식을 사용한 다층구조를 사용하였다. 기생소자의 크기와 폼 물질의 높이를 조절함으로서 광대역 특성을 얻었다. 또한, 급전선 하단 λ/4 위치에 도체판을 사용함으로서 후방 방사를 줄였다. 단일 방사소자의 대역폭은 VSWR 1.3이하에서 550MHz를 얻었다. 제작된 1$\times$4 배열 안테나의 대역폭은 VSWR 1.3이하에서 460MHz, 안테나 이득은 11.15~12.15dBi, 전후방비는 30dB를 얻었다.

• Structural Engineering and Mechanics
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• 제90권4호
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• pp.357-370
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• 2024

Due to the fact that the mechanism of the effects of temperature and initial geometric imperfection on low-velocity impact problem of axially moving plates is not yet clear, the present paper is to fill the gap. In the present paper, the nonlinear dynamic behavior of axially moving imperfect graphene platelet reinforced metal foams (GPLRMF) plates subjected to lowvelocity impact in thermal environment is analyzed. The equivalent physical parameters of GPLRMF plates are estimated based on the Halpin-Tsai equation and the mixing rule. Combining Kirchhoff plate theory and the modified nonlinear Hertz contact theory, the nonlinear governing equations of GPLRMF plates are derived. Under the condition of simply supported boundary, the nonlinear control equation is discretized with the help of Gallekin method. The correctness of the proposed model is verified by comparison with the existing results. Finally, the time history curves of contact force and transverse center displacement are obtained by using the fourth order Runge-Kutta method. Through detailed parameter research, the effects of graphene platelet (GPL) distribution mode, foam distribution mode, GPL weight fraction, foam coefficient, axial moving speed, prestressing force, temperature changes, damping coefficient, initial geometric defect, radius and initial velocity of the impactor on the nonlinear impact problem are explored. The results indicate that temperature changes and initial geometric imperfections have significant impacts.