가속열화시험에 따른 케이블의 수명평가에 대한 신뢰성분석

정진동(Jin-Dong Jeong),이지연(Ji-Yeon Lee),강신동(Sin-Dong Kang),김재호(Jae-Ho Kim) 한국조명·전기설비학회 2020 조명·전기설비학회논문지 Vol.34 No.11

This paper comparatively analyzed the characteristics of the insulation resistance of TFR-8(Tray Frame Retardant power cable for fire service) cables according to accelerated degradation temperature and thermal stress application methods to ensure the validity of the accelerated degradation life test using the Arrhenius model. The study derived accelerated degradation times according to accelerated degradation temperatures by applying the Arrhenius model, and it manufactured cable specimens with equivalent lifetimes of 10, 20, 30, and 40 years using a forced-convection oven. The insulation resistance decreased as the temperature increased, and the measured insulation resistance of equivalent-lifetime cables were similar. The experimental results of constant thermal stress and step-stress application methods were also similar. These results verify the validity of the correlation between the Arrhenius model’s temperature and the chemical reaction rate. However, the accelerated degradation time could vary according to the calculation method of activation energy, which requires follow-up studies.

Electrochemical impedance analysis with transmission line model for accelerated carbon corrosion in polymer electrolyte membrane fuel cells

Jung, Jeawoo,Chung, Young-Hoon,Park, Hee-Young,Han, Jonghee,Kim, Hyoung-Juhn,Henkensmeier, Dirk,Yoo, Sung Jong,Kim, Jin Young,Lee, So Young,Song, Kwang Ho,Park, Hyun S.,Jang, Jong Hyun Elsevier 2018 International journal of hydrogen energy Vol.43 No.32

<P><B>Abstract</B></P> <P>The effects of varying the applied voltage and relative humidity of feed gases in degradation tests of polymer electrolyte membrane fuel cells (PEMFCs) were analyzed using electrochemical impedance spectroscopy (EIS). A transmission line model that considers the proton-transport resistance in the cathode catalyst layer was used to analyze impedance spectra obtained from degraded PEMFCs. As the applied cell voltage was increased from 1.3 to 1.5 V to induce accelerated degradation, the cell performance decayed significantly due to increased charge- and proton-transfer resistance. The PEMFC degradation was more pronounce at higher relative humidity (RH), i.e. 100% RH, as compared with that observed under 50% RH. Furthermore, changes in the charge transfer resistance of the electrode accompanied changes in the ionic conductivity in the PEMFC catalyst layer. Although the initial ionic and charge-transfer resistances in the catalyst layer were lower under higher RH conditions, the impedance results indicated that the performance degradation was more significant at higher water contents in the electrode due to the consequential carbon corrosion, especially when higher voltages, i.e. 1.5 V, were applied to the PEMFC single cell.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Accelerated degradation tests (ADTs) were performed on PEMFC single cells. </LI> <LI> Effects of relative humidity (RH) and cell voltages in ADTs on PEMFC were studied. </LI> <LI> The degradation was studied by transmission line model in impedance spectroscopy. </LI> <LI> At higher RH in ADT, increased charge- and proton-transfer resistance was observed. </LI> </UL> </P>

무은 솔더의 신뢰성 평가에 관한 연구

김종민(Jong-min Kim),김기영(Gi-young Kim),김강동(Kang-dong Kim),김선진(Seon-jin Kim),장중순(Joong Soon Jang) 한국신뢰성학회 2013 신뢰성응용연구 Vol.13 No.2

The solder is any of various fusible alloys, usually tin and lead, used to join metallic parts that provide the contact between the chip package and the printed circuit board. Solder plays an important role of electrical signals to communicate between the two components. In this study, two kinds of Ag-free solder as sample is made to conduct the thermal shock test and the high humidity temperature test. Low resistance is measured to estimate crack size of solder, using daisy chain. The low speed shear test is also performed to analyze strength of solder. The appropriate degradation model is estimated using the result data. Depending on the composition of solder, lifetime estimation is conducted by adopted degradation model. The lifetime estimated two kinds of Ag-free solder is compared with expected lifetime of Sn-Ag-Cu solder. The result is that both Ag-free composition are more reliable than Sn-Ag-Cu solder.

Stochastic Modeling of Cavitation Erosion in Francis Runner

Quentin Chatenet,Martin Gagnon,Laurent Ton-That,Emmanuel Remy,Mitra Fouladirad,Antoine Tahan 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.2

Reaction turbines, of which Francis turbines, constitute a large proportion of low and medium head turbines installed in hydropower plants. Managing these machines represents a real challenge in terms of efficiency, competitiveness and demands on the energy market. Turbines runner blades exhibit loss of performance from damage due to several reasons. One common source of damage is erosion due to the cavitation phenomenon. Indeed, at a given operating region, rapid changes of velocity can create bubbles in the water flow due to local low pressures. When cavitation bubbles reach pressure recovery, they collapse and may induce wear or erosion in these regions. Even if this phenomenon has been intensively studied in the past decades, cavitation erosion is not fully understood as it is driven by several parameters such as flow dynamic, turbine design, environment, or material properties. Some of these parameters can be studied in laboratory to compare materials resistance between each other. This article aims to model the cavitation by a stochastic model using erosion experimental data observed in the laboratory. The benefit of such models is to consider both the uncertainties and natural fluctuations of the phenomenon. With the proposed framework, the study will highlight the differences observed in cavitation erosion experiments of two common materials used to manufacture Francis’s runners. This study is the first step in a project aiming at the prediction of turbines mass loss due to cavitation erosion on actual operating Francis turbines.

Stochastic Modeling of Cavitation Erosion in Francis Runner

Quentin Chatenet,Martin Gagnon,Emmanuel Remy,Mitra Fouladirad,Antoine Tahan 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.1

Reaction turbines, of which Francis turbines, constitute a large proportion of low and medium head turbines installed in hydropower plants. Managing these machines represents a real challenge in terms of efficiency, competitiveness and demands on the energy market. Turbines runner blades exhibit loss of performance from damage due to several reasons. One common source of damage is erosion due to the cavitation phenomenon. Indeed, at a given operating region, rap id changes of velocity can create bubbles in the water flow due to local low pressures. When cavitation bubbles reach pressure recovery, they collapse and may induce wear or erosion in these regions. Even if this phenomenon has been intensively studied in the past decades, cavitation erosion is not fully understood as it is driven by several parameters such as flow dynamic, turbine design, environment, or material properties. Some of these parameters can be studied in laboratory to compare materials resistance between each other. This article aims to model the cavitation by a stochastic model using erosion experimental data observed in the laboratory. The benefit of such models is to consider both the uncertainties and natural fluctuations of the phenomenon. With the proposed framework, the study will highlight the differences observed in cavitation erosion experiments of two common materials used to manufacture Francis’s runners. This study is the first step in a project aiming at the prediction of turbines mass loss due to cavitation erosion on actual operating Francis turbines.

Effects of series resistance and interface properties on the operation of AlGaN/GaN high electron mobility transistors

Jeon, Dae-Young,Kim, Do-Kywn,Park, So Jeong,Koh, Yumin,Cho, Chu-Young,Kim, Gyu-Tae,Park, Kyung-Ho Elsevier 2018 MICROELECTRONIC ENGINEERING Vol.199 No.-

<P><B>Abstract</B></P> <P>The AlGaN/GaN high electron mobility transistor (HEMT) is considered a promising device for high-power, high-frequency, and high-temperature applications, as well as high-sensitivity sensors. However, several issues related to mobility, interface properties, and series resistance need to be clarified for a better understanding of the physical operation of AlGaN/GaN HEMTs and for further optimization of their performance. In this work, the electrical properties of AlGaN/GaN HEMTs, including the effects of series resistance, and interface properties with mobility degradation factors were investigated in detail. In addition, the low-frequency noise behavior of AlGaN/GaN HEMTs was examined with a carrier number fluctuation model that considered series resistance effects.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Electrical characteristics of AlGaN/GaN HEMTs with several parameters were investigated in detail. </LI> <LI> Series resistance (R<SUB>sd</SUB>) effect significantly causing degradation of effective mobility was de-embedded. </LI> <LI> Gate-to-channel capacitance (C<SUB>gc</SUB>) was obtained with eliminating the parasitic offset capacitance. </LI> <LI> Mobility degradation factors were discussed with interface quality issues. </LI> <LI> Carrier number fluctuation model with considering R<SUB>sd</SUB> effects explained well 1/f noise behavior of AlGaN/GaN HEMTs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

BaTiO₃ 기반의 적층 세라믹 캐피시터 (Multi-Layer Ceramic Capacitors)의 절연저항 열화 메커니즘과 신뢰성 분석 동향

이규탁(Ku-Tak Lee),천진성(Jinsung Chun),조욱(Wook Jo) 한국세라믹학회 2023 세라미스트 Vol.26 No.2

The demand for high performance multilayer ceramic capacitors (MLCCs) has rapidly increased keeping up with the recent trends in electronics seeking better performance per volume. It follows that thinning of dielectric layers of MLCC and atomization of powders have become two most challenging issues these days. However, it is well known that these two approaches are not free from reliability issues. In this brief review, we introduce the commonly accepted models that explain how dielectric materials fail during operation and how to evaluate the lifetime of MLCCs with a real world example.

일계이차모멘트법에 의한 기존 철근콘크리트 구조물의 구조안전성평가

남호윤 ( Nam Ho-yun ),서대원 ( Seo Dae-won ),한범석 ( Han Byum-seok ),유석형 ( Yoo Suk-hyeong ),신성우 ( Shin Sung-woo ) 한국구조물진단유지관리공학회 2008 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.12 No.2

In reinforced concrete(RC) members, since the concrete compressive strength, section geometry, reinforcing steel yield strength, and bar placement parameters are all random, the ultimate strength, R, of the member is a random variable. Therefore, uncertainties exist in the RC member behavior. Uncertainties arises from variations in loads and material strength properties, dimensions, natural and man-made hazards, insufficient knowledge, and human error in design and construction. Therefore, this paper is aimed to analyze reinforced concrete members by Advanced First Second Moment (AFOSM) method using statistical characterization of variables. Also, this paper was executed to analyze structural resistance degradation model for the existing reinforced concrete Structures.