Carbon nanofiber-reinforced polymeric nanocomposites

Changwoon Jang,John Hutchins,Jaesang Yu 한국탄소학회 2013 Carbon Letters Vol.14 No.4

Five vapor-grown carbon nanofiber (VGCNF) reinforced vinyl ester (VE) nanocomposite configurations were fabricated, imaged, and mechanically tested in order to obtain information on the influence and the interactions of the role of the microstructure at lower length scales on the observed continuum level properties/response. Three independent variables (the nanofiber weight fraction and two types of nanofiber mixing techniques) were chosen to be varied from low, middle, and high values at equally spaced intervals. Multiple mixing techniques were studied to gain insight into the effect of mixing on the VGCNF dispersion within the VE matrix. The point count method was used for both lower length-scale imaging techniques to provide quantitative approximations of the magnitude and the distribution of such lower length-scale features. Finally, an inverse relationship was shown to exist between the stiffness and strength properties of the resulting nanocomposites under uniaxial quasistatic compression loading.

Creep lifetime prediction of solder joint for heat sink assembly

Han, Changwoon,Oh, Chulmin,Park, Nochang,Hong, Wonsik Elsevier 2010 Microelectronics and reliability Vol.50 No.9

<P><B>Abstract</B></P><P>The heat sink assembly in a server station is anticipated to creep to fail at the solder joint under a constant load and temperature condition. To predict the lifetime of solder joint in the system, accelerated creep-rupture tests are conducted. Three loads of 4, 6, and 8kg and temperatures of 35, 55, and 65°C are selected for the tests. Larson–Miller model is adopted for the lifetime prediction, which requires tested lifetime data and stress analyses for the solder joint. An FE model for the stress analyses is developed and validated experimentally. Analyzed Larson–Miller constants show different tendency in the 8kg load cases. Extensive failure analyses on the failed solder joints reveal the transition of failure mechanism at 8kg load cases from the intergranular to the transgranular creep. Using only the validated test data of 4 and 6kg load cases, creep lifetime prediction model for the solder joint in the heat sink assembly is developed and applied for a field condition.</P>

열·습도 복합하중에서의 유연성 전자모듈에 대한 구조해석

한창운(Changwoon Han),오철민(Chulmin Oh),홍원식(Wonsik Hong) 대한기계학회 2013 大韓機械學會論文集A Vol.37 No.5

이동용 전자기기에 적용 가능한 유연성 전자모듈이 롤투롤 공정에 의해 개발되었다. 개발된 전자 모듈은 모듈 내의 폴리이미드층이 유연성 기판 역할을 하고 그 사이에 동선과 이방성도전필름과 박막 실리콘 칩과 모듈의 봉지재 역할을 하는 접착재료로 구성된다. 개발된 유연성 전자모듈의 신뢰성을 평가하기 위하여 일련의 인증시험을 수행하였다. 시험수행 결과 열·습도 복합하중 조건인 오토클레이브 시험 후에 시편 모듈 내에 박리가 발생하였다. 오토클레이브 시험에서 열과 습기가 유연성 전자모듈에 어떤 응력을 발생시키는지를 범용 유한요소 프로그램으로 연구하였다. 열·흡습 복합하중조건에서 열과 흡습에 의한 영향을 분리하여 상대적으로 평가해 보기 위하여 오토클레이브 조건 중 온도조건에 해당하는 121°C 온도조건 만을 적용하여 해석을 별도 수행하고 두 결과를 비교하였다. 또한 비교 해석결과를 바탕으로 유연성 전자모듈의 고장메커니즘을 추정하였다. A bendable electronic module is developed. In this module, thin silicon electronic chips are embedded in a polymer-based encapsulating adhesive between flexible copper-clad polyimide layers. During the qualification test of a harshly thermal-hygroscopic complex loading condition, delaminations occur inside the module layers. A finite element model is developed for the module. To investigate the effect of hygroscopic stress on delamination, the results of the thermal and thermal-hygroscopic loads are compared. The analysis results reveal that the hygroscopic effect more strongly affects delamination than does the thermal effect. The potential failure mechanisms of the module are investigated based on the stress analysis.

Error analysis of the phase-shifting technique when applied to shadow moiré

Han, Changwoon,Han, Bongtae The Optical Society 2006 Applied Optics Vol.45 No.6

<P>An exact solution for the intensity distribution of shadow moiré fringes produced by a broad spectrum light is presented. A mathematical study quantifies errors in fractional fringe orders determined by the phase-shifting technique, and its validity is corroborated experimentally. The errors vary cyclically as the distance between the reference grating and the specimen increases. The amplitude of the maximum error is approximately 0.017 fringe, which defines the theoretical limit of resolution enhancement offered by the phase-shifting technique.</P>

내정전기방전 관점에서의 BLDC 모터 설계신뢰성 연구

한창운(Changwoon Han),황순미(Soon-mi Hwang),송병석(Byeongsuk Song) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10

The reliability of two differently-designed BLDC motors are investigated and compared to choose one of them for the fan application in a home appliance. A series of reliability tests are conducted to the BLDC motors including high temperature storage, low temperature storage, temperature cycling, humidity test, vibration test, drop test, and electrostatic discharge (ESD) test according to IEC 61000-4-2. Both of the BLDC motors don’t show any significant degradation of their characteristics after tests except ESD test. After ESD test, one type of motors shows 100% immunity but another type of motor shows 35% of failure. To investigate the cause of the failure in ESD test, a commercial ESD simulation program is used in modeling the two types of motors in electric overstress environment. Simulation results explain the vulnerable design for ESD in a BLDC motor and suggest that the design of controlling module in BLDC motor affects significantly ESD immunity.

거울을 이용한 단안렌즈 스테레오 비전

구창운(Changwoon Koo),김충원(Choongwon Kim) 한국통신학회 1999 한국통신학회 학술대회논문집 Vol.1999 No.11

Snap-in 터미널 타입 콘덴서의 자동 정렬 및 검사 시스템

구창운(Changwoon Koo),전정희(Junghee Jun),김충원(Choongwon Kim) 한국통신학회 1998 한국통신학회 학술대회논문집 Vol.1998 No.11

Effects of curing systems on the mechanical and chemical ageing resistance properties of gasket compounds based on ethylene-propylene-diene-termonomer rubber in a simulated fuel cell environment

Nah, Changwoon,Kim, Seung Gyeom,Shibulal, Gopi Sathi,Yoo, Yong Hwan,Mensah, Bismark,Jeong, Byeong-Heon,Hong, Bo Ki,Ahn, Jou-Hyeon Elsevier 2015 International journal of hydrogen energy Vol.40 No.33

<P><B>Abstract</B></P> <P>Ethylene-propylene-diene-termonomer (EPDM) rubber based fuel cell gasket compounds have been designed and explored the effects of various vulcanization systems on different properties. Three types of sulphur-accelerated vulcanization systems such as conventional vulcanization (con), semi-efficient vulcanization (sev) and efficient vulcanization (ev) and also a peroxide vulcanization system were employed in this study. The curing characteristics, tensile, hardness and compression set properties of the cured compounds were evaluated. The crosslink density was assessed by equilibrium swelling method in dodecane. The chemical stability of the cured EPDM compounds was also evaluated through an accelerated durability test (ADT) using a solution (1 M H<SUB>2</SUB>SO<SUB>4</SUB> + 10 ppm HF) very close to the fuel cell atmosphere. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM) were employed to investigate the chemical and physical changes of the cured EPDM compounds before and after exposure to the ADT solution over time. The results indicate that the EPDM compounds cured with peroxide exhibit the highest crosslink density with lowest compression set value at both room temperature and at elevated temperature. The FTIR and the corresponding SEM results show no significant chemical degradation of the peroxide cured EPDM compounds due to ADT ageing.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We examine the long-term ageing resistance of rubber vulcanizates in a simulated fuel cell environment. </LI> <LI> We monitor the chemical and physical change during ageing. </LI> <LI> The peroxide cure system shows much enhanced resistance to ageing than sulphur cure system. </LI> <LI> The cure additive such as ZnO in the sulphur cure system can negatively affect the performance of fuel cell. </LI> </UL> </P>

온도변화 환경에서 칩저항 실장용 유·무연솔더의 수명모델 검증연구

한창운(Changwoon Han) 대한기계학회 2016 大韓機械學會論文集A Vol.40 No.3

최근에 온도변화 환경에서 칩저항 실장용 유·무연 솔더의 수명예측모델이 개발되었다. 개발된 수명예측모델에 의하면 가속조건에서는 칩저항 실장 무연솔더가 유연솔더보다 수명이 적은 것으로 나타나지만, 실제조건에서는 무연솔더의 신뢰성이 유연솔더보다 우수하다. 본 연구에서는 개발된 수명예측 모델의 검증 연구를 수행한다. 수명예측모델을 다른 칩저항 실장 유·무연 솔더 시험 결과에 적용하고 비교하기 위해서, 유한요소모델을 개발하고 시험 온도사이클 조건을 적용한다. 변형율 에너지 밀도를 계산하고 수명을 예측한다. 마지막으로 유·무연 솔더에 대해서 예측결과를 시험결과와 비교한다. 검증결과는 개발된 수명예측모델이 사용 가능한 범위에서 수명을 예측할 수 있음을 보인다. Recently, life prediction models for Pb-based and Pb-free solders used in chip resistor assemblies under thermal cycling have been introduced. The models suggest that the field lifetimes of Pb-free solders would be better than those of Pb-based solders when used for chip resistors under thermal cycling conditions, while the lifetime of the chip assemblies under accelerated test conditions show a reverse relationship. In this study, the prediction models were verified by applying the model to another research case. Finite element models were built, thermal cycling conditions were applied, and the energy densities were calculated. Finally, life prediction analysis was conducted for the cases where Pb-based and Pb-free solders were used. The prediction results were then compared with the test data of the case. It was verified that the predictions of the developed life cycle models are on the practical scale.

태양전지 어레이에 적용 가능한 열화모듈 검출방법 개발

한창운(Changwoon Han),박승일(Seungil Park),이현석(Hyeonseok Lee) 대한기계학회 2018 大韓機械學會論文集A Vol.42 No.5

태양광 발전소는 효율적 전기 생산을 위해 태양전지 모듈을 직렬 및 병렬로 연결한 태양전지 어레이로 구성된다. 어레이를 구성하는 개별 태양광 모듈은 시간에 지남에 따라 열화가 진행되며, 태양광 어레이의 발전효율은 열화가 진행된 모듈의 발전효율에 따라 결정된다. 본 연구에서는 태양전지 모듈을 어레이에서 분리하지 않고, 열화가 진행된 모듈을 검출하는 방법을 제안한다. 이 방법은 태양광 모듈에 반투명 가림막을 설치하여 모듈의 전기적 특성을 인위적으로 변경하며 어레이 전체의 출력 곡선을 측정하고 상호 비교한다. 방법의 효과를 분석하고 제안 방법의 검증을 위해서 회로 시뮬레이션을 실시한다. 또한, 실제 태양전지 어레이에 대해서 본 방법을 적용하고 방법의 타당성을 검증한다. Solar cell modules are connected in serial and parallel in a photovoltaic system. All the solar cell modules degrade over time, and the most degraded module in an array decides the output level of the array. In this study, we suggest a health-monitoring method that makes it possible to detect the most degraded module in an array without separating the module from the array. We suggest placing a nontransparent film on a module in an array to create an artificial shading effect. It needs to monitor the current-voltage curve of the string while placing the film on the next one. We show analytically that the most degraded module can be detected by comparing all the array current-voltage curves. We demonstrated the method using an outdoor photovoltaic array.