• Transactions of Materials Processing
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• v.29 no.6
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• pp.338-346
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• 2020

A V-bending test was performed in order to predict springback of high-strength steel sheets under various conditions. The results of V-Bending test were analyzed with artificial neural networks and FE-simulation, respectively, for the tool design. The results of design are discussed. The bending test result using the tool designed with artificial neural networks was about 92˚. However, the bending test result using the tool designed FE-simulation was about 94.5˚. Artificial neural networks are a useful tool along with FE-simulation in predicting springback.

• Transactions of Materials Processing
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• v.13 no.5
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• pp.409-414
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• 2004

TRIP steel has got attention in automobile industry because of its high strength and high formability. However, the information on deformation behavior of TRIP steel, including bending and springback, is not enough until now. In this research, the V-die bending experiment and analysis have been done to obtain the information of springback of TRIP steel. And a new numerical method, where elastic modulus is varied with the change of the strain, was suggested. Tensile test for TRIP steel was done to get tensile properties as well as strain dependency of elastic modulus of the material. Strain-dependency of elastic modulus was used the numerical analysis of V-die bending and unbending process to predict springback amount. The results were compared with experiment, showing reasonable agreement. Through the analysis of V-die bending as well as draw bending of TRIP steel, the proposed scheme with variable elastic modulus was proven to well predict the deformation behavior of TRIP steel during bending and springback.

• Transactions of Materials Processing
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• v.27 no.3
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• pp.177-183
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• 2018

The influence of electric current on the springback characteristics of AZX311 magnesium alloy and martensitic steel after V-bending test is investigated. Various pulsed electric currents are applied into the specimens followed by a V-bending test, and the changes in the springback angle are measured. In order to evaluate not only the thermal effect but also the athermal effect of electric current on the springback angle, the temperature rises resulting from the applied electric current are measured for all test conditions. As a result, it was found that the springback is significantly decreased as the current density increases. As for the martensitic steel, since the dislocation recovery immoderately occurs at a high electric current density condition of $80A/mm^2$, the optimal current density condition should be required.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.4
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• pp.443-449
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• 2012

Nanoskins were fabricated on a Ti-6Al-4V material by carrying out various surface treatments, i.e., deep rolling, laser shot peening, and ultrasonic nanocrystal surface modification (UNSM). These surface treatments are newly developed techniques and are becoming more popular for industrial applications. Fatigue tests were carried out using material test system (MTS); these tests included the axial loading tension-compression fatigue test (R = -1, RT, 5 Hz, sinusoidal wave) and rotating bending fatigue test (R = -1, RT, 3200 rpm). The analysis of the crack initiation pattern in the UNSM-treated material indicated that the crack was interior originating in the axial loading tension-compression cycle, and was surface originating in the bending fatigue test. UNSM treatment significantly improved the fatigue strength for the regime of above $10^6$ cycles that S-N curve of rotating bending stress clearly show the performance of a 5 mm titanium specimen after UNSM treatment is similar to that of an untreated 6 mm titanium specimen.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.6
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• pp.778-783
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• 2015

We studied about the strength characteristics of the FRP bonding method due to reduce accident on the oceans and protect life for my people. We test tension and bending strength of butt joint, lap joint, V-scarf joint, X-scarf joint. The result of test, it's pattern is similar both tension and bending strength. Tension strength and bending strength was excellent in order to X-scarf-butt joint-V-scarf-lap joint. The tension strength is the best properties X-scarf showed a 57% strength rate of the basic material, and bending strength showed a 77% strength rate of the basic material. Overall, the X-scarf 12t joint has most excellent properties of tension and bending strength. The lap joint has worst properties of tension and bending strength. We have to test having different over-lay of V-scarf and X-scarf joint each 12t, 16t, 20t. V-scarf of 20t over-lay has excellent character of tension and bending strength. But X-scarf of 12t over-lay has excellent character of tension and bending strength. The results are shown to the contrary. The ship is received a lot of stress. it's hard to compare a direction both actual and test. But we can acknowledge material basic characteristic of strength through tension and bending test. We give the four repair method; butt joint, lap joint, V-scarf joint, X-scarf joint and the reduced ratio in comparison with basic material; In addition give the separated data for V-scarf and X-scarf characteristic of 12t, 16t, 20t overlay length. For our study repair man can select good repair method in his work station.

• Journal of the Korea Convergence Society
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• v.13 no.3
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• pp.197-202
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• 2022

The CZTS solar cell is a thin film solar cell using an absorption layer composed of Cu, Zn, Sn, Se, and S, and is cheaper than a CIGS solar cell using In and Ga and more eco-friendly than a perovskite and CdTe solar cell using Pb and Cd. In this study, we conducted a bending test for flexible CZTS solar cells. Experiments were conducted in the direction of inner benidng with compressive stress and outer bending with tensile stress, and during the number of bending 1,000 times with a radius of curvature of 50 mmR, the efficiency of the solar cell decreased by up to 12.7%, and the biggest cause of efficiency reduction in both directions was a large decrease in parallel resistance.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.616-618
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• 2007

This paper describes the mechanical and electrical test on HVDC submarine cable, Flexible Repair Joint and termination for 180kV. This HVDC submarine cable was manufactured using LS cable's unique skill and would be applied the HVDC submarine cable system in korea. The performance test consist of mechanical test and electrical test. The tensile bending test and tensile test was done as the mechanical test and Electrical test is DC voltage and Impulse test. The tensile bending test carried out 6 times(double of specified times) for maximum reliability. The DC test voltage is $\pm$400kV/1hr. We estimate the lower limit of DC breakdown voltage is 600kV. The impulse test voltage is $\pm$800kV/10shots. The type of developed cables is the MI type. Its insulation consist of paper tapes impregnated with a high viscosity oil. The development of new HVDC cable is available for HVDC underground or submarine power transmission. The developed HVDC cable, FRJ and termination have passed the mechanical and electrical test successfully and showed excellent performance.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.998-1001
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• 2009

A new flexible TFT backplane structure with improved mechanical reliability is proposed. Amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistors based on this structure have been fabricated on a polyimide substrate, and the resultant mechanical durability has been evaluated in a cyclic bending test. The panel can withstand 10,000 bending cycles at a bending radius of 5 mm without any noticeable TFT degradation. After 10K bending cycles, the change of threshold voltage, mobility, sub-threshold slope, and gate leakage current were only -0.22V, -0.13$cm^2$/V-s, -0.05V/decade, and $-3.05{\times}10^{-13}A$, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.181.2-181.2
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• 2016

OLED 소자는 발광 방향에 따라 Bottom Emission 방식과 Top Emission 방식으로 나뉜다. 이 중 대면적 OLED TV 적용에 개구율이 더 높은 Top Emission방식을 선호하는 추세이다. 높은 개구율을 가진 Top Emission OLED소자를 위해서는 투명하고 전도성이 높은 캐소드가 중요하다. 본 연구에서는 Themal Evaporation 시스템을 이용하여 증착한 $SnO_2/Ag-Pd-Cu(APC)/SnO_2$ hybrid 전극의 특성을 연구하고 Oxide/Metal/Oxide(OMO) hybrid 박막의 bending mechanism을 제시하였다. base pressure는 $1{\times}10^{-6}Torr$로 고정하고 $SnO_2$ 박막은 0.34A / 0.32V, APC 박막은 0.46A / 0.40V의 power로 성막하였다. APC와 $SnO_2$의 두께를 변수로 OMO 전극을 제작하였고 그 전기적, 광학적 특성을 Hall measurement, UV/Visible spectroscopy을 이용하여 분석하고 Figure of merit 값을 바탕으로 최적 두께를 설정하였다. UPS(Ultraviolet Photoelectron Spectroscopy) 분석으로 $SnO_2/APC/SnO_2$ 전극의 일함수을 통해 투명 cathode로 쓰였을 때 $SnO_2$ 층이 buffer layer역할을 함을 확인하였다. XPS(X-ray photoelectron spectroscopy)를 이용하여 정성분석과 정량분석을 하였고 OMO hybrid 전극의 bending mechanism 연구를 위해 다양한 bending test (Inner/Outer dynamic fatigue test, twisting test, rolling test)를 진행하였다. 물리적 힘이 가해진 OMO hybrid 전극의 표면과 구조는 FE-SEM(Field Emission Scanning Electron Microscope) 분석을 통해서 확인할 수 있었다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.11
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• pp.1024-1028
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• 2008

It is important that study on cryogenic electrical insulation design to develop the cold dielectric(CD) type HTS cable because the cable is operated under the high voltage environment in cryogenic temperature. This paper proposes two types of insulation design to carry out the maximum insulation design for 154 kV-class HT cable. The proposed insulation design method takes into consideration AC and lightning impulse withstand voltage so as to prevent AC breakdown for power frequency operating voltage during operating the cable and breakdown for lightning impulse voltage. The final insulation thickness is determined by selecting high value out of two insulation thickness calculated through the two insulation design methods. And we researched electrical insulation characteristics of HTS cable according to bending ratio and the number of bending.