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서봉현,석지원,Bong Hyun Seo,Yonas Tsegaye Megra,Ji Won Suk 한국복합재료학회 2023 Composites research Vol.36 No.5
To enhance the performance of graphene-based devices, it is of great importance to better understand the interfacial interaction of graphene with its underlying substrates. In this study, the adhesion energy of monolayer graphene placed on dielectric substrates was characterized using mode I fracture tests. Large-area monolayer graphene was synthesized on copper foil using chemical vapor deposition (CVD) with methane and hydrogen. The synthesized graphene was placed on target dielectric substrates using polymer-assisted wet transfer technique. The monolayer graphene placed on a substrate was mechanically delaminated from the dielectric substrate by mode I fracture tests using double cantilever beam configuration. The obtained force-displacement curves were analyzed to estimate the adhesion energies, showing 1.13 ± 0.12 J/m<sup>2</sup> for silicon dioxide and 2.90 ± 0.08 J/m<sup>2</sup> for silicon nitride. This work provides the quantitative measurement of the interfacial interactions of CVD-grown graphene with dielectric substrates.
서봉현,이호상,Seo, Bong-Hyun,Lee, Ho-Sang 한국금형공학회 2016 한국금형공학회지 Vol.10 No.2
Injection molded thermoplastic parts may need to be coated to facilitate paint adhesion, or to satisfy other surface property requirements, such as appearance, durability, and weather resistance. In this paper, a two-component polyurethane metering system was developed for the simultaneous injection and surface coating of a plastic substrate. The system was composed of storage tanks, feed pumps, axial piston pumps, mixing head. The tank was designed to be double-jacket structured and fabricated for polyol and isocyanate, respectively. A temperature chamber was used to maintain the material temperature to be $80^{\circ}C$ during flowing from storage tank to mixing head. Inside the chamber, feed pump, low pressure filter, high pressure pump, high pressure filter, pressure sensor, flow meter were installed. A mixing head of L-type was used for homogeneous mixing of polyol and isocyanate. Inside the mixing head, a cartridge heater and a temperature sensor were installed to control the temperature of the materials. The flow rate of axial-piston pump was controlled by using closed-loop feedback control algorithm. The input flow-rates were compared with the measured values. The output error was 6.7% for open-loop control, whereas the error was below 2.2% for closed-loop control. In addition, the pressure generated through mixing-head nozzle increased with increasing flow rate. It was found that the pressure drop between metering pump and mixing-head nozzle was almost 10 bar.
자동차용 암레스트의 미세다공 사출성형 공정에 대한 연구
서봉현(Bong Hyun Seo),노상호(Sang Ho Noh),최광복(Kwang Bok Choi),진광진(Kwang Jin Jin),박상언(Sang Un Park) 대한기계학회 2018 大韓機械學會論文集A Vol.42 No.6
최근 자동차 제조업계에서는 국제 환경규제에 대응하기 위한 온실가스 저감 및 주행중 VOCs 감소를 위하여 경량화에 대한 연구를 활발히 진행 중에 있다. 본 연구에서는 자동차용 도어 암레스트 제품의 경량화를 위하여 열가소성 폴리프로필렌 수지와 화학적 발포제를 적용하여 미세다공 사출성형 공정을 구현하였다. 성형 해석을 통하여 제품의 결함과 성형성을 예측하였으며, 이를 미세다공 사출성형 공정에 적용하여 도어 암레스트 시제품을 제작하였다. 사출성형 시 발포 셀 성장을 위하여 코어백 기술을 적용하였고, 해석 결과와 실제 제품의 SEM 촬영을 통한 발포 셀 크기를 분석하였다. Automotive manufacturers have been developing lightweight vehicles of late to reduce CO₂ and volatile organic compound (VOC) emissions and to meet international environmental regulations. In this study, we focused on a microcell injection molding process to develop lightweight automotive armrests made of thermoplastic polypropylene and chemical blowing agents. Prototype door armrests were fabricated using the microcell injection molding process, and part defects and moldability were predicted through a molding analysis. Core-back technology was used in the injection molding process to increase the cell growth. In addition, the cell sizes were investigated using scanning electron microscopy for actual part and molding simulations.
Examination of Implicit Interactivity in Wiki-based Learning in University
서봉현(Bong-Hyun Seo),강인애(In-Ae Kang),남선우(Sun-Woo Nam) 한국컴퓨터정보학회 2010 한국컴퓨터정보학회 학술발표논문집 Vol.18 No.2
The arrival of the Web 2.0 age, which is characterized by such key words as participation, sharing and openness, provides a learning environment in which both instructors and students can experience interactivity. In the educational area, we are particularly witnessing a growing interest in the social software like Wiki as one of the communication tools that reflects the characteristics of Web 2.0 and focuses on the interactivity with others. Based on this background, this study aims to examine into the meanings of interactivity inherent in the Wiki-based learning by studying such cases where Wiki is being used as a learning tool. For the purpose of our study, we practiced the Wiki-based learning method on the study subjects of the 17 junior students from U- University and 18 junior students from K- University during their 2009 fall semester teacher training courses. Through a comprehensive analysis of the questionnaires, interviews, Interactivity Measurement Diagram, examinations on the Wiki uses, Daily Self-reflection Records, and any other materials collected throughout the program, we could garner the following results: First, most of the students acknowledged that the use of Wiki was a useful communication means and helped promote their interactivity during their learning activities. Second, the interactivity of the Wiki-based learning was found to be more dynamic in the team-based projects or the community-based Wiki uses than in the instructor-oriented cases. Third, the Wiki-based learning is judged effective in expanding the scope of thinking and improving the learning capabilities through the collaborative knowledge-building process. The educational employment of the social software like Wiki in this web 2.0 age has great potentials for the true establishment of the learner-oriented learning environment, which has long remained at a standstill.
자동차용 암레스트의 미세다공 사출성형 공정에 대한 연구
서봉현(Bong-Hyun Seo),노상호(Sang-Ho Noh),김선아(Sun-Ah Kim),진광진(Kwang-Jin Jin),박상언(Sang-Un Park) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
Recently, Automotive manufacturers are researching on a light-weight vehicle for reducing CO₂ and VOCs(Volatile Organic Compounds) emissions to meet International Environmental Regulations. As a methods for light-weighting the automobile interiors, the design and process changes such as thickness reduction of products and/or blow foaming injection molding process using foaming agents are considered. However these changes have many problems during the injection molding process such as short-shot, deformation and etc. In order to solve these problems, we are focused on Micro-cell Injection Molding Process to secure the product quality and to establish the process conditions.