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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.
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.
고장예지를 위한 온도사이클시험에서 칩저항 실장솔더의 고장메커니즘 연구
한창운(Changwoon Han),박노창(Nohchang Park),홍원식(Wonsik Hong) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
A thermal cycle test was conducted on the chip resistor solder joint with a real-time failure monitoring. To detect the failure of the chip resistor solder joint during the test, the resistance between both ends of resistor is monitored until failure occurs. Monitored resistance was first observed to fluctuate linearly according to the temperature change. Initial aberration of the resistance occurred during the temperature decreasing time of the thermal cycle. More serious change of the resistance followed after some cycles at the temperature increasing time of the thermal cycle. To explain the failure patterns of solder joint, a mechanism for the solder failure was suggested and proved through FE simulations. Based on the explained failure mechanism, it was shown that a prognostics for the solder failure can be implemented by monitoring the resistance change in a thermal cycle condition.
한창운(Changwoon Han),박승일(SeungIl Park),이수연(Suyeon Lee) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.4
태양 전지 모듈의 수명 또는 전력 보증 기간은 모듈의 신뢰성 측면 뿐만 아니라 태양 에너지 소요 비용 절감에 중요한 요소이다. 태양 전지 제조업체는 현재 실리콘 태양광 모듈에 대해 25 년 전력 보증을 제공하고 있지만, 이는 곧 연장되어야 한다. 본 연구는 열 사이클링 하에서 실리콘 태양전지 모듈의 수명을 늘리기 위해 기존 모듈에 대한 수치 해석과 신뢰성 최적화를 수행한다. 첫째, 기존 태양전지 모듈에 대해서 재료의 점성과 온도 의존성을 고려하여 수치모델을 개발한다. 둘째, 열 피로에 대한 솔더의 수명 예측 모델을 조사하고 수명의 결정 변수를 선택한다. 셋째, 모듈 내 설계 변수 변화에 따른 일련의 민감도 연구를 수행한다. 다음으로, 연구 결과로부터 신뢰성이 강화되도록 태양전지 모듈의 신뢰성 최적설계를 수행한다. 마지막으로, 새로운 최적설계안의 수명을 분석하고 기존 모듈과 비교한다. 신뢰성이 강화된 신뢰성최적설계 모듈의 수명은 기존 모듈에 비해 크게 늘어날 것으로 예상된다. The lifetime of solar cell modules, or power warranty time, is not only a reliability measure but also an important factor for the reduction of solar energy costs. Solar cell manufacturers currently provide 25 years power warranty to Si solar modules, but it should be extended. In this study, to enhance the lifetime of silicon solar modules under thermal cycling, numerical analysis and optimization are conducted on a conventionally designed module. First, the conventional module is numerically modeled with the temperature-dependent material properties including the viscosity of EVA and solder layers. Second, solder lifetime prediction models under thermal fatigue are investigated and a critical measure of the lifetime in the thermal fatigue is selected. Third, a series of sensitivity studies with the measure is conducted by the variation of module design parameters. Next, a reliability-enhanced design of solar cell modules is suggested from the study results. Finally, the lifetime of the new design is analyzed and compared with the conventional module under thermal cycling. The lifetime of the reliability-optimized module design is expected to increase significantly compared to that of the conventional module.
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>
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>