• 한국세라믹학회지
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• 제51권5호
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• pp.399-405
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• 2014

Porous alumina with different porosities, 5.2 - 47.5%, were coated with cover-glass having a thickness of $160{\mu}m$, using epoxy adhesive. We investigated the effect of the porosity of the substrate layer on the crack initiation load, and the size of cracks propagated in the coating layer. Hertzian indentations were used to evaluate the damage behavior under a constrained loading condition. Typically, two types of cracks, ring cracks and radial cracks, were observed on the surface of the glass/porous alumina structure. Indentation stress-strain curves, crack initiation loads, crack propagation sizes, and flexural strengths were investigated as a function of porosities. The results indicated that a porosity of less than 30% and a higher substrate elastic modulus were beneficial at suppressing cracks occurrence and propagation. We expect lightweight mechanical components with high strength can be successfully fabricated by coating and controlling porosities in the substrate layer.

• 한국정밀공학회지
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• 제2권2호
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• pp.69-75
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• 1985

The object of this study is to discuss the effect of cutting fluid on the mechanism of chip formation in orthogonal cutting. Rehbinder effect has been known as a phenomenon, the reduction of mechanical strength, when the metal is exposed in a polar organic environment or the surface of metal is coated with some polar organic substances. About the cause of Rehbinder effect there have been many different ideas by Rehbinder, Merchant, Shaw, Sakakida and etc. In this report, the effects of surface active medium (magic ink) upon the mechanism of chip formation on the orthogonal cutting of copper and the mechanical properties of the work material are experimentally discussed with constant rake angle. Under the condition of polar organic environment the experimental results are as follows; 1) The chip thickness becomes thinner and slip line pitch on the free surface of chip becomes smaller than that of dried cutting area. 2) The order of alternation of cutting ratio was changed. 3) The friction angle on the tool face is not affected by the depth of cut. 4) The cutting force and shear strain on the shear plane decrease remarkably, therefore the work material must be embrittled under polar organic environment.

• Journal of Microbiology and Biotechnology
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• 제19권8호
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• pp.836-844
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• 2009

A denitrification bacterium was isolated from riverbed soil and identified as Ochrobactrum sp., whose specific enzymes for denitrification metabolism were biochemically assayed or confirmed with specific coding genes. The denitrification activity of strain G3-1 was proportional to glucose/nitrate balance, which was consistent with the theoretical balance (0.5). The modified graphite felt cathode with neutral red, which functions as a solid electron mediator, enhanced the electron transfer from electrode to bacterial cell. The porous carbon anode was coated with a ceramic membrane and cellulose acetate film in order to permit the penetration of water molecules from the catholyte to the outside through anode, which functions as an air anode. A non-compartmented electrochemical bioreactor (NCEB) comprised of a solid electron mediator and an air anode was employed for cultivation of G3-1 cells. The intact G3-1 cells were immobilized in the solid electron mediator, by which denitrification activity was greatly increased at the lower glucose/nitrate balance than the theoretical balance (0.5). Metabolic stability of the intact G3-1 cells immobilized in the solid electron mediator was extended to 20 days, even at a glucose/nitrate balance of 0.1.

• 전기전자학회논문지
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• 제20권4호
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• pp.412-415
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• 2016

본 연구에서는 노인의 온열치료에 적용가능한 웨어러블 면상발열체를 제작하고, 그 발열특성을 조사하였다. 웨어러블 면상발열체는 인듐 주석 산화물 나노입자를 유리섬유위에 코팅하고, 에코플렉스 안에 삽입하여 제작하였다. 제작된 면상발열체는 30%의 신축 스트레인상태에서도 발열온도 변화가 10%이내로 안정적으로 동작하였다. 또한 웨어러블 면상발열체를 사람의 손목에 부착하여 동작시켰을 때, 2분 안에 손목의 온도가 $35^{\circ}C$에서 $43^{\circ}C$로 상승하였다.

• 대한기계학회논문집A
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• 제31권8호
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• pp.847-854
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• 2007

The battery electrode of a mobile phone is made of layered polymer coated on aluminum foils and the hot rolling process is applied to increase the density per volume of an electrode for a high capacity battery. The flatness of batteries surfaces should be less than $2{\mu}m$. To satisfy the required flatness, the deformation of roll surface due to bending and heating of the roll should be minimized. Complicated hot oil paths of $100^{\circ}C$ inside the roll are required for heating the polymer layers. FEA was used to calculate thermal deformations and temperatures distributions of the roller. Based on FEA, a modified surface curvature called a crown roll was suggested and this gave the area of 30% improved flatness compared with a flat roll. The flat roll satisfied the flatness of $2{\mu}m$ in the length of 340 mm and the crown roll resulted in the longer length of 460 mm. Experiments to measure the temperature distribution and thermal strain were performed and compared with FEA. There were only 6% difference between two results.

• 한국환경농학회지
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• 제25권3호
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• pp.228-235
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• 2006

Pseudomonas aeruginosa $GRC_2$, siderophore-producing strain, inhibited growth of Macrophomina phaseolina in vitro and reduced charcoal rot in seeds of Brassica juncea in field when coated with adaptive strains. P. aeruginosa $GRC_2$ and Azotobacter chroococcum $AC_1$ produced indole-3-acetic acid and solubilized insoluble phosphate. A. chroococcum $AC_1$ fixed nitrogen asymbiotically. Urea and diammonium phosphateadaptive variant strains of P. aeruginosa and A. chroococcum strongly inhibited M. phaseolina in comparison to parental strains. Bacterization of seeds induced seed germination, seedling growth, and enhanced yield of B. juncea by 10.87% as compared to full doses of urea and diammonium phosphate. Both adaptive strains of chemical fertilizers aggressively colonized roots, showing effectiveness to growth and developments of B. juncea.

• 소성∙가공
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• 제17권3호
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• pp.170-181
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• 2008

The shape of rectangular cup used for Ni-MH(Nickel-coated Metal Hydrogen) battery for hybrid car looks quite simple, but the forming process of extruding and setting up process design are highly difficult. Furthermore, there are few concrete reports on the rectangular deep drawn cup as part of hybrid vehicles till now. In this study, process design for rectangular cup in the multi-stage deep drawing process is carried out, and FE analysis is also preformed based on the result of the process design. From the simulation result, some unexpected problems such as earing, wrinkling and excessive thickness changes of the intermediate blank occurred. To overcome these failures, a series of modification for punch shape in the forming process design are completed and applied. Considering the modified punch shape in the multi-stage deep drawing process, additional FE analysis is also carried out and the simulation result is verified in view of the deformed shape, thickness change and effective strain distribution. The result of FE analysis with the improved process design confirmed not only reducing thinning of wall and possibilities of failure but also improving the quality of drawing product through the modification of punch shape.

• 한국정밀공학회지
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• 제22권10호
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• pp.186-194
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• 2005

This study was designed to investigate the mechanical properties of the coating layer on electronic galvanized sheet steel as a part of the ongoing research on the coated steel. Those properties were determined using nano-indentation, the finite element method, and artificial neural networks. First and foremost, the load-displacement curve (the loading-unloading curve) of coatings was derived from a nano-indentation test by CSM (continuous stiffness measurement) and was used to measure the elastic modulus and hardness of the coating layer. The properties derived were applied in FE simulations of a nano-indentation test, and the analytical results were compared with the experimental result. A numerical model for FE simulations was established for the coating layer and the substrate separately. Finally, to determine the mechanical properties of the coating, such as the stress-strain curve, functional equations of loading and unloading curves were introduced and computed using the neural networks method. The results show errors within $5\%$ in comparison with the load-displacement measured by a nano-indentation test.

• 한국염색가공학회지
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• 제11권4호
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• pp.50-56
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• 1999

The adhesive properties of polyester cord in rubber matrix were investigated according to the surface modification. The polyester cord was oxidized in sodium hypochlorite solution, and graft-polymerized with acrylic acid under the irradiation with ultraviolet light, and then coated with resorcinol-formaldehyde latex (RFL). The modified surface was checked with scanning electron microscope. The adhesive properties were measured by the full-Out method, and evaluated with regard to the energy of adhesion and the maximum load. The polyester was not oxidized in sodium hypochlorite solution, so the surface was not able to etch to produce the coarse topology. As the concentration of acrylic acid and the reaction time were increased, the graft yields were also increased. It was considered that the acrylic acid would swell the polyester and diffuse easily to the inner side of substrate. The adhesive properties of polyeser to rubber matrix were affected by the surface condition. Namely, the maximum load was almost same, but the energy of adhesion was rather higher In the polyester grafted with acrylic acid than in control one. We concluded that the flexible aliphatic chains of polyacrylic acid situated in the interface of cord and rubber matrix were distributed well the stress and strain all over the filler resulting the high energy of adhesion.

• 소성∙가공
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• 제32권3호
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• pp.122-128
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• 2023

As electric vehicles (EV) have increasingly replaced the conventional vehicles with internal combustion engines (ICE), most of automotive makers are actively devoting to the technology development of EV parts. Accordingly, the manufacturing process for power source has been also shifting from engine/transmission to EV motor/reducer system. However, lack of experience in developing the EV motor still remains as a technical challenge. In this paper, we employed the forming simulation based on finite element modeling to solve this problem. In particular, in order to increase the accuracy of the forming simulation, we introduced the elastic-plastic constitutive model parameters for polymer-copper hybrid wire by investigating the individual strain-stress curves, and elastic modulus of polymer and copper. Then, the reliability of modeling procedure was confirmed by comparing the simulated results with experiments. Finally, the identified mechanical properties and finite element modeling were applied to a hairpin forming process, which involves multiple deformation paths such as bending, pressing, widening, and twisting. The proposed numerical approach can replace common experience or experiment based trials by reducing production time and cost in the future.