• Journal of Energy Engineering
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• v.23 no.2
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• pp.149-157
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• 2014

The steam generator tubes of nuclear power plants have various types of corrosion failures during the plant operation. The stress corrosion cracking which occurs on the outer surface of tube is called the secondary side stress corrosion cracking and mainly occurs in the expansion-transition area of tube. The causes are the concentration of impurities by the sludge pile-up related to the geometry of its region and the residual stress by tube expansion in the process of steam generator manufacturing. Especially the directionality and sizes of residual stresses are differed according to the tube expansion methods and the direction and the frequency of tube cracks depend on their characteristics. In bases on the plant experiences, it is notified that circumferential cracks of tubes expanded with explosive expansion method are dominantly occurred compared to those of tubes done with hydraulic expansion one. Therefore in this study, according to tube expansion methods frequencies and sizes of tube cracks with specific direction are compared by means of accelerated immersion test and also the crack morphology and the specific chemicals from water-chemistry environment are observed through the fracture surface examination.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1320-1325
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• 1995

For hydrogen-cooled large turbine generators, partial discharges in ground wall insulations are suppressed by high hydrogen pressure. The first goal of the experiment is to investigate the effect of hydrogen pressure on partial discharge activity and aging rate in turbine generator winding insulations. A series of tests have been performed on two groups of the accelerated aging experiments. The first group of stator windings was aged under hydrogen pressure of 4 atm while the second group of stator windings was aged under air atmosphere. The stator windings aged under air atmosphere suffer from larger partial discharge magnitude with larger voids at high electrical stress than those under hydrogen pressure. The second goal of the experiment is to evaluate the validity of on-line measurement technique which is normally measured under hydrogen environment. The test results show that further experiments are needed to apply the on-line scheme to turbine generator being under high hydrogen pressure.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.76.2-76.2
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• 2010

The gas diffusion layer is the key component of the proton exchange membrane fuel cell because it directly affect to the mass transport mechanism and dynamic behavior of the cell. In this study, the effects of GDL aging on the transient response of the PEM fuel cell is systematically investigated using current step transient response analysis under different stoichiometric ratios and humidity conditions. With GDLs aged by the accelerated stress test, the effects of hydrophobicity and structural changes due to carbon loss in the GDL on the transient response of PEM fuel cells are determined. The degraded GDLs that had uneven hydrophobicity distributions cause local water flooding inside the GDL and induce lower and unstable voltage responses after load changes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.5 no.5
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• pp.462-465
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• 2004

After 6 month of using, cracking of gas exhaustion bag cage of Type 304 stainless steel wire for Al melting reverberatory furnace was founded in welds. Analysis of crack causes in the wire were tested by electrochemical method, SEM images of structure and analysis of composition. Resulted from the test, it could be observed that cracks in the welds were a accelerated by formed polythionic acid on surface of bag cage in sensitized region of HAZ, tensile stress and using environment.

• Journal of Microbiology and Biotechnology
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• v.29 no.4
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• pp.538-547
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• 2019

The aim of the present study was to evaluate the effects of two well-known natural antioxidants, vitamin C (VC) and vitamin E (VE), on the antifungal activity of honokiol against Candida albicans. The broth microdilution method was employed to test the antifungal activities of honokiol with or without antioxidants in the medium against C. albicans strain. Intracellular reactive oxygen species and lipid peroxidation were determined by fluorescence staining assay. Mitochondrial dysfunction was assessed by detecting the mitochondrial DNA and the mitochondrial membrane potential. We observed that VC could significantly potentiate the antifungal activities of honokiol while VE reduced the effectiveness of honokiol against C. albicans. In addition, VC accelerated honokiol-induced mitochondrial dysfunction and inhibited glycolysis leading to a decrease in cellular ATP. However, VE could protect against mitochondrial membrane lipid peroxidation and rescue mitochondrial function after honokiol treatment. Our research provides new insight into the understanding of the action mechanism of honokiol and VC combination against C. albicans.

• Journal of Korean Society of Steel Construction
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• v.24 no.6
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• pp.725-734
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• 2012

A new modular pier system using concrete filled circular steel tubes was suggested to realize modular bridge substructures for accelerated bridge construction. Structural details and connection details were proposed by connection multiple concrete filled tubes (CFT) for standardized products of fabrication, delivery and erection. Static tests were performed for the modular pier with suggested details under lateral load conditions for weak and strong axes. Due to the eccentricity by the bracing system, the modular pier showed 5.23 times higher flexural stiffness and 6 times greater flexural strength from the test. It is proper for the rational design to evaluate stress and deformation by frame modeling of the modular CFT pier. Structural capacity of the pier can be obtained by adjusting the spacing of the CFT columns. Design recommendations were derived from the test.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.5
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• pp.215-221
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• 2014

In this paper, the improved power durability test system and method for an reliability analysis of SAW device is proposed and the failure mechanism through failure analysis is analyzed. As a result of the failure analysis using microscope, SEM and EDX, the failure mechanism of the SAW device is electromigration due to joule heating under high current density and high temperature condition. The electromigration makes voids and hillocks in the IDT electrode and the voids and hillocks can lead to short circuit and open circuit faults, respectively, increasing the insertion loss of an SAW filter. The accelerated life testing of the SAW filter for 450MHz CDMA application using the proposed power durability test system and method is carried out. $B_{10}$ lifetime of the SAW filter using Eyring model and Weibull distribution is estimated as about 98,500 hours.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.10
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• pp.424-429
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• 2018

In this study, an expansion joint that is susceptible to waterhammer was tested for its vibration durability. The operation data for the hydraulic actuator was the expansion length of the expansion joint when the waterhammer occurred. In the case of the vibration durability test, the internal temperature status of the expansion joint was assumed to be a stress factor and a lifespan prediction model was assumed to follow the Arrhenius model. A test was carried out by increasing the internal temperature status at $30^{\circ}C$, $50^{\circ}C$, and $65^{\circ}C$. By a linear transformation of the lifespan data for each temperature, a constant value and activation energy coefficient was induced for the Arrhenius equation and verified by comparing the value of a lifetime prediction model with the experimental value at $85^{\circ}C$. The failure modes of the ongoing or finished test were leakage, bellows separation, and internal deformation. In the future, a composite lifespan prediction model, including two more stress factors, will be developed.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.2
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• pp.165-172
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• 2013

Power generating unit structures are designed and built to meet standard to secure its safety for expected life time. As the structures have been exposed to combined environment, degradation of structure material is accelerated and it can cause unexpected damage; evaluating precise mechanical properties of weak site like welded area is an essential research area as it is directly connected to safety issues. Existing measuring technique like tensile test requires specific size in testing specimen yet it is destructive method which is hard to apply on running structures. To overcome above mentioned limitation, IIT is getting limelight as it is non-destructive and simple method. In this study, latest technique is introduced to evaluate tensile property and residual stress by analyzing stress field occurs under the indenter while IIT is performed. Test on welded area, the weak site of nuclear structures have been practiced and confirmed that IIT can be usefully applied to evaluate integrity in industry.

• Korean Journal of Materials Research
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• v.22 no.9
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• pp.454-458
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• 2012

Various adhesive materials are used in flip chip packaging for electrical interconnection and structural reinforcement. In cases of COF(chip on film) packages, low temperature bonding adhesive is currently needed for the utilization of low thermal resistance substrate films, such as PEN(polyethylene naphthalate) and PET(polyethylene terephthalate). In this study, the effects of anhydride and dihydrazide hardeners on the low-temperature snap cure behavior of epoxy based non-conductive pastes(NCPs) were investigated to reduce flip chip bonding temperature. Dynamic DSC(differential scanning calorimetry) and isothermal DEA(dielectric analysis) results showed that the curing rate of MHHPA(hexahydro-4-methylphthalic anhydride) at $160^{\circ}C$ was faster than that of ADH(adipic dihydrazide) when considering the onset and peak curing temperatures. In a die shear test performed after flip chip bonding, however, ADH-containing formulations indicated faster trends in reaching saturated bond strength values due to the post curing effect. More enhanced HAST(highly accelerated stress test) reliability could be achieved in an assembly having a higher initial bond strength and, thus, MHHPA is considered to be a more effective hardener than ADH for low temperature snap cure NCPs.