• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.222-225
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• 2006

The effect of lubrication on the development of textures and Microstructure was studied by different lubricating condition during hot rolling of AA1050 aluminum alloy. Hot rolling without lubrication led to the evolution of the pronounced through-thickness texture gradients, whereas hot rolling with lubrication gave rise to the formation of uniform rolling texture in the whole thickness layer. The variation of texture and microstructure according to hot rolling condition are investigated by X-ray diffractometer (XRD) and Electron Back-Scattered Diffraction (EBSD). The experimental results were discussed base on the finite element method (FEM) simulation. FEM calculation reveals that a larger friction between roll and sheet causes the deviated strain state from a plane strain leading to the formation of shear textures in the thickness layers close to the surface.

• 소성∙가공
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• 제24권5호
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• pp.354-360
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• 2015

AHSS (Advanced High Strength Steels) has been increasingly employed by global automotive OEMs in order to satisfy strengthened regulations and reduce weight for fuel efficiency. Hot stamping using boron steels in AHSS increases not only formability but also strength. The typical hot-stamped automotive part is the center pillar that is critical for vehicle side impact. However, the hot-stamped part can be risky for the passenger safety caused by brittle fracture under a vehicle collision. The high power diode laser is suitable for the heat treatment giving AHSS increased elongation that prevents brittle fracture in car crash. Therefore, local softening by laser heat treatment for energy absorption area on the hot-stamped part improves crash-worthiness.

• 한국세라믹학회지
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• 제16권2호
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• pp.69-76
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• 1979

This study attempted to characterize the powder and sintered specimen of Mn-Zn ferrite that was prepared by Hot Petroleum Drying Method. The results of the experiment were as follows: 1. The mixed sulfate powder prepared by Hot Petroleum Drying Method was homogeneous and very reactive. The ferrite formation of this powder occurred at lower temperature than the one prepared by Sulfate Dry Mixing Method. 2. The calcined oxide powder prepared by Hot Petroleum Drying Method was found to be agglomerated, and therefore it was very difficult to compact this powder. 3. The sintered density was 4.95g/㎤, 97% of the theoretical density, when the specimen was prepared by Hot Petroleum Drying method, calcined at 90$0^{\circ}C$ in air for 3h, sintered at 1,30$0^{\circ}C$ in air for 3h, and then cooled in nitrogen. 4. The discontinuous grain growth occurred at lower temperature in the specimen prepared by Hot Petroleum Dyring Method than in the one prepared by Sulfate Dry Mixing Method. The discontinuous grain growth was considered to be due to the presence of liquid formed by addition of CaO and $SiO_2$.

• 한국정밀공학회지
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• 제22권8호
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• pp.159-164
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• 2005

The Hot Embossing Lithography(HEL) as a method fur the fabrication of the nanostructure with polymer is becoming increasingly important because of its simple process, low cost, high replication fidelity and relatively high throughput. In this paper, we carried out experimental studies and numerical simulations in order to understand the viscous flow of the polymer (PMMA) film during the hot embossing process. To grasp the characteristics of the micro patterning rheology by process parameters (embossing temperature, pressure and time), we have carried out various experiments by using the nickel-coated master fabricated by the deep RIE process and the plasma sputtering. During the hot embossing process, we have observed the characteristics of the viscoelastic behavior of polymer. Also, the viscous flow during the hot embossing process has been simulated by the continuum based FDM(Finite Difference Method) analysis considering the micro effect, such as a surface tension and a contact angle.

• 대한기계학회논문집A
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• 제24권3호
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• pp.735-742
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• 2000

Densification behaviors of mixed metal powder under high temperature were investigated. Experimental data of mixed copper and tool steel powder with various volume fractions of Cu powder were obtained under hot isostatic pressing and hot pressing. By mixing the creep potentials of McMeeking and co-workers and of Abouaf and co-workers originally for pure powder, the mixed creep potentials with various volume fractions of Cu powder were employed in the constitutive models. The constitutive equations were implemented into a finite element program (ABAQUS) to compare with experimental data for densification of mixed powder under hot isostatic pressing and hot pressing. Finite element calculations by using the creep potentials of Abouaf and co-workers agreed reasonably well with experimental data, however, those by McMeeking and co-workers underestimate experimental data as observed in the case of pure metal powders.

• 대한기계학회논문집A
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• 제33권11호
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• pp.1267-1273
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• 2009

Hot press forming can produce high-strength components by rapidly cooling between closed punch and die after hot forming using quenchable boron steel austenized in a furnace. In the hot press forming process, the cooling rate is influenced by the size, position and arrangement of the cooling channel and the file condition of cooling water in the die. Also, mechanical properties of the final components and operation time are related to cooling rate. Therefore, the design of optimized cooling channel is one of the most important works. In this paper, the effect of position and size of the cooling channel on the cooling rate was investigated by using design of experiment and FE analysis in hot press bending process. Therefore the optimum cooling channel ratio was presented in the HPB.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2003년도 춘계학술대회 논문집
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• pp.260-264
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• 2003

The application of solar energy, in the field of alternative energy, was on the increase tendency. In the case of advanced nations, through continuous R&D, solar-heat hot-water-boiler with high efficiency has been used for the house and the industrial process on business, advanced nations on reached up the experimental stage of solar generation system. But the actual circumstance of the domestic has been not accomplished the popularization of solar-heat hot-water-boiler and the settlement of it which is the fundamental stage of the solar energy usage. This trouble, the domestic was flooded with small enterprise for producing solar-heat hot-water-boiler, was caused by the popularization and the production without verification of performance. To supply the monitoring program for evaluating solar-heat hot-water-boiler, this research was purpose to improve the technical development of the enterprise for producing solar-heat hot-water-boiler and served as an aid f3r the enlargement and the popularization on solar energy.

• 한국시뮬레이션학회논문지
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• 제17권2호
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• pp.13-19
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• 2008

본 연구에서는 드레인 부근의 채널 영역에서 접합 전계를 줄이는 Buffered deposition 구조의 소자를 제안하였다. Buffered deposition 구조의 소자 제작은 첫 번째 게이트를 식각한 후에 NM1(N-type Minor1) 이온주입을 하고 다시 HLD막과 질화막을 덮어 식각하여 제작하였다. 이러한 Buffered deposition 구조는 전계를 줄이기 위한 버퍼층으로 되어 있으며 Buffered deposition 소자의 여러 가지 구조의 Hot carrier 수명을 비교하였으며 열화 특성도 분석하여 10년간의 Hot carrier 수명을 만족함을 증명하였다.

• Journal of Electrical Engineering and Technology
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• 제8권1호
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• pp.156-162
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• 2013

This paper measures the hot spot temperatures in a single-phase, 154 kV, 15/20 MVA power transformer filled with natural ester fluid using optical fiber sensors and compares them with those calculated by conventional heat run tests. A total of 14 optical fiber sensors were installed on the high-voltage and low-voltage windings to measure the hot spot temperatures. In addition, three thermocouples were installed in the transformer to measure the temperature distribution during the heat run tests. In the low-voltage winding, the hot spot temperature was $108.4^{\circ}C$, calculated by the conventional heat run test. However, the hot spot temperature measured using the optical fiber sensor was $129.4^{\circ}C$ between turns 2 and 3 on the upper side of the low-voltage winding. Therefore, the hot spot temperature of the low-voltage winding measured using the optical fiber sensor was $21.0^{\circ}C$ higher than that calculated by the conventional heat run test.

• 대한기계학회논문집B
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• 제20권11호
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• pp.3630-3638
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• 1996

An experimental study has been conducted to explore the behaviors of the radiative ignition of polymethylmetacrylate(PMMA) in a confined enclosure such as the ignition delay time, PMMA surface temperature, the ignition location and the ignition process. In addition, the effects of hot wall orientation on the ignition delay and PMMA surface temperature were studied. When the hot wall is located at the bottom, ignition delay time is the shortest. Ignition surface temperature becomes the lowest for the hot top wall case. These are due to buoyancy effect. Since the radiative heat flux of hot wall is rather lower than laser source, the ignition is considered to be controlled by the mixing process. Therefore, the ignition location, where appropriate mixture of fuel and oxygen exists, occurs near the hot wall. The flame propagates along the hot wall where there exists sufficient oxygen.