• 한국생산제조학회지
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• 제19권2호
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• pp.235-240
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• 2010

The recent trend of vehicle design aims at crash safety and environmentally-friendly aspect. For the crash safety aspect, energy absorbing members should be absorbed with collision energy sufficiently. But vehicle structure must be light weight for the environmentally-friendly aspect, in order to improve fuel efficiency and to reduce tail gas emission. Therefore, the light weight of vehicle must be achieved in a status of securing safety of crash. An aluminum or CFRP (Carbon Fiber Reinforced Plastics) is representative one among the light-weight materials. In this study, impact collapse behavior of circular hybrid thin-walled member is evaluated. The hybrid members are manufactured by wrapping CFRP prepreg sheets outside the aluminum circular members in the autoclave. Because the CFRP is an anisotropic material whose mechanical properties change with its stacking condition, special attention is given to the effects of the stacking condition on the collapse behavior evaluation of the hybrid thin-walled member. Collapse mode and energy absorption capability of the hybrid thin-walled member are analyzed with change of the fiber orientation angle and interface number.

• Composites Research
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• 제26권5호
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• pp.295-302
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• 2013

본 연구에서는 차량용 Al5052/CFRP 복합재를 U-채널 몰드에서 컴프레션 몰딩 공정을 통해 제작하였다. Al5052는 샌드블라스팅을 통해 표면처리를 하였다. 표면처리를 하지 않은 판재와 표면거칠기(Ra)가 $1.85{\mu}m$ 및, $4.25{\mu}m$인 Al5052판재를 이용하여 실험을 수행하였다. 표면거칠기가 Al5052/CFRP 복합재의 접착성과 기계적 특성에 대한 영향을 전단시험과 굽힘실험을 통하여 평가하였다. 전단 시험에서는 표면거칠기가 $1.85{\mu}m$ 와 $4.25{\mu}m$ 시험편이 표면처리를 하지 않은 시험편보다 각각 3, 5배의 전단강도의 증가를 보였다. 굽힘시험에서는 표면처리를 하지 않았을 때 굽힘강도가 200 MPa에서 표면처리 후 400 MPa로 증가함을 알 수 있었다.

• Structural Engineering and Mechanics
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• 제78권5호
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• pp.611-622
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• 2021

Composite material-due to low density-causes weight savings, which results in lower fuel consumption of transport vehicles. The aim of the research was to change the existing base-plate of the aluminum airplane container with the composite sandwich plate in order to reduce the weight of the containers of cargo aircrafts. The newly constructed sandwich plate consists of aluminum honeycomb core and composite face-sheets. The face-sheets consist of glass or carbon or hybrid fiber layers. The orientations of the fibers in the face-sheets were 0°, 90° and ±45°. Multi-objective optimization method was elaborated for the newly constructed sandwich plates. Based on the design aim, the importance of the objective functions (weight and cost of sandwich plates) was the same (50%). During the optimization nine design constraints were considered: stiffness, deflection, facing stress, core shear stress, skin stress, plate buckling, shear crimping, skin wrinkling, intracell buckling. The design variables were core thickness and number of layers of the face-sheets. During the optimization both the Weighted Normalized Method of the Excel Solver and the Genetic Algorithm Solver of Matlab software were applied. The mechanical properties of composite face-sheets were calculated by Laminator software according to the Classical Lamination Plate Theory and Tsai-Hill failure criteria. The main added-value of the study is that the multi-objective optimization method was elaborated for the newly constructed sandwich structures. It was confirmed that the optimal new composite sandwich construction-due to weight savings and lower fuel consumption of cargo aircrafts - is more advantageous than conventional all-aluminum container.

• 대한기계학회논문집A
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• 제26권11호
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• pp.2328-2335
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• 2002

A hybrid composite material has many potential usage due to the high specific strength and the resistance to fatigue, when compared to other composite materials such as fiber reinforced plastic(FRP) and metal matrix composite(MMC). However, the fracture mechanism of hybrid composite material is extremely complicated because of the bonding structure of metals and FRP. In this study, Al 7075 sheets and carbon epoxy preprags were used to fabricate the hybrid composite. Recently, nondestructive technique has been used to evaluate the fracture mechanism of these composite materials. AE technique was used to clarify the microscopic damage behavior and failure mechanism of A17075/CFRP hybrid composite. It was found that AE paralneters such as AE event, energy and amplitude were effective to evaluate the failure process of Al 7075/CFRP composite. In addition, the relationship between the AE signal and the characteristics of fracture surface using optical microscope was discussed.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.10.2-10.2
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• 2011

The design and synthesis of protein-like polymers is a fundamental challenge in materials science. A biomimetic approach is to explore the impact of monomer sequence on non-natural polymer structure and function. We present the aqueous self-assembly of two peptoid polymers into extremely thin two-dimensional (2D) crystalline sheets directed by periodic amphiphilicity, electrostatic recognition and aromatic interactions. Peptoids are sequence-specific, oligo-N-substituted glycine polymers designed to mimic the structure and functionality of proteins. Mixing a 1:1 ratio of two oppositely charged peptoid 36 mers of a specific sequence in aqueous solution results in the formation of giant, free-floating sheets with only 2.7 nm thickness. Direct visualization of aligned individual peptoid chains in the sheet structure was achieved using aberration-corrected transmission electron microscopy. Specific binding of a protein to ligand-functionalized sheets was also demonstrated. The synthetic flexibility and biocompatibility of peptoids provide a flexible and robust platform for integrating functionality into defined 2D nanostructures. In the later part of my talk, we describe the use of metal ions to construct two-dimensional hybrid films that have the ability to self-heal. Incubation of biomimetic peptoid polymers with specific divalent metal ions results in the spontaneous formation of uniform multilayers at the air-water interface. We anticipate that ease of synthesis and transfer of these two-dimensional materials may have many potential applications in catalysis, gas storage and sensing, optics, nanomaterial synthesis, and environmentally responsive scaffolds.

• Steel and Composite Structures
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• 제30권3호
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• pp.231-251
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• 2019

In the present study, a numerical and experimental investigation has been carried out on the seismic behavior of RC columns of a bridge which damaged under corrosive environments and retrofitted by various techniques including combined application of CFRP sheets and steel profiles. A novel hybrid retrofitting procedure, including the application of inner steel profiles and outer peripheral CFRP sheets, has been proposed for strengthening purpose. Seven large-scale RC columns of a Girder Bridge have been tested in the laboratory under the influence of simultaneous application of constant axial load and the lateral cyclic displacements. Having verified the finite element modeling, using ABAQUS software, the effects of important parameters such as the corrosion percentage of steel rebars and the number of CFRP layers have been evaluated. Based on the results, retrofitting of RC columns of the bridge with the proposed technique was effective in improving some measures of structural performance such as lateral strength degradation and higher energy absorption capability. However, the displacement ductility was not considerably improved whereas the elastic stiffness of the specimens has been increased.

• 한국산학기술학회논문지
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• 제22권5호
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• pp.530-536
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• 2021

본 논문에서는 전자기기 등에서 전자파 차폐 및 방열소재로 많이 채택되는 동 메쉬 시트와 천연그라파이트 시트를 감압 접착제없이 합지시켜 개발된 차폐 및 방열의 기능을 동시에 가지는 하이브리드시트의 성능 측정결과를 제시하였다. 객관적인 방열 성능을 확인하기 위해 2개의 다른 제품들과 수직 및 수평 열전도도를 각각 측정하여 결과를 비교하였으며, 전자파 차폐 성능은 CISPR 11규격에 따른 복사방출시험을 3m 전자파 무향실에서 진행하여 확인하였다. 수직 열전도도의 경우 제안된 하이브리드 시트가 방열코팅이 된 알루미늄 시트 대비 약 8.63배, 감압 접착제로 인조 그라파이트를 합지시킨 구리 시트에 비해 18.7배 높은 수준이였으며, 수평 열전도도는 인조 그라파이트를 합지시킨 구리 시트에 비해 약 0.64배, 방열 코팅된 알루미늄 시트에 대해서는 약 1.76배로 나타났다. 동일한 열원에서 각 시트들을 적용 후 측정한 결과에서는 제안된 하이브리드 시트가 열방출 기능이 가장 우수하였고 복사방출시험에서는 방사노이즈들이 상당 부분 제거되는 결과를 얻었다.

• 열처리공학회지
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• 제21권3호
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• pp.144-149
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• 2008

It has been reported that copper and copper alloys have a large anisotropy of functional properties such as electrical, thermal and mechanical properties, which means that the texture of polycrystalline alloy should be considered to achieve better properties. In this study, the determination of grain growth orientation and texture formation in the cold-rolled, heat-treated and Ni-plated hybrid copper sheets was investigated. Grain growth direction and texture formation were analyzed by the X-ray pole figure. The influence of texture on the mechanical properties could be quantitatively confirmed by the results from the orientation distribution function and the tensile test. The heat-treated texture in the cold-rolled hybrid copper sheet is also investigated and discussed.

• Journal of Welding and Joining
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• 제24권4호
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• pp.22-26
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• 2006

In lap welding of zinc-coated steel, porosity formation is one of most significant weld defects, which is caused by zinc vapor generated between the steel sheets. Various solutions have been proposed in the past years but development of more effective method is a worthwhile subject to be investigated. In this study, autogenous laser welding and laser-TIG hybrid welding was applied to the lap welding of zinc-coated steel without gap, and weld pool behaviors were observed by using high speed camera and the porosity generation mechanism was analyzed. The weld defects were successfully eliminated by laser-TIG hybrid welding. This is because the leading TIG arc partially melted the upper sheet and vaporized/oxidized the coated zinc on the lapped surfaces prior to the trailing laser illuminating the specimen.

• 한국기계가공학회지
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• 제12권6호
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• pp.30-36
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• 2013

An FFD(flexible fine die) is an embossed mold that consists of a thin plate ranging from 0.6 to 3 mm in thickness. FFDs are primarily used for cutting LCD films and F-PCB sheets. In the high-speed micro-milling process of flexible fine dies, the lubrication and cooling of the cutting edges is very important from the aspect of eco machining and cutting performance. In this paper, a comparative study of tool wear and surface roughness between cutting fluid and hybrid lubrication for eco-machining of FFD was conducted for processes of high-speed machining of highly hardened material (STC5, HRC52). Especially, the incorporated fluid method for eco machining, in which the cutting performances can be simultaneously measured, was introduced. The machining results show that hybrid lubrication, instead of conventional cutting fluid, leads to excellent tool wear and surface roughness and represents the proper conditions for eco micro-machining of flexible fine dies.