• Journal of Korean Society of Industrial and Systems Engineering
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• v.38 no.4
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• pp.142-148
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• 2015

Due to advancements in technology and manufacturing capability, it is not uncommon that life tests yield no or few failures at low stress levels. In these situations it is difficult to analyse lifetime data and make meaningful inferences about product or system reliability. For some products or systems whose performance characteristics degrade over time, a failure is said to have occurred when a performance characteristic crosses a critical threshold. The measurements of the degradation characteristic contain much useful and credible information about product or system reliability. Degradation measurements of the performance characteristics of an unfailed unit at different times can directly relate reliability measures to physical characteristics. Reliability prediction based on physical performance measures can be an efficient and alternative method to estimate for some highly reliable parts or systems. If the degradation process and the distance between the last measurement and a specified threshold can be established, the remaining useful life is predicted in advance. In turn, this prediction leads to just in time maintenance decision to protect systems. In this paper, we describe techniques for mapping product or system which has degrading performance parameter to the associated classical reliability measures in the performance domain. This paper described a general modeling and analysis procedure for reliability prediction based on one dominant degradation performance characteristic considering pseudo degradation performance life trend model. This pseudo degradation trend model is based on probability modeling of a failure mechanism degradation trend and comparison of a projected distribution to pre-defined critical soft failure point in time or cycle.

• Journal of Korean Society of Water and Wastewater
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• v.33 no.4
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• pp.243-250
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• 2019

This objective of this study was to investigate the degradation characteristics of phenol, a refractory substance, by using a submerged dielectric barrier discharge (DBD) plasma reactor. To indirectly determine the concentration of active species produced in the DBD plasma, the dissolved ozone was measured. To investigate the phenol degradation characteristics, the phenol and chemical oxygen demand (COD) concentrations were evaluated based on pH and the discharge power. The dissolved ozone was measured based on the air flow rate and power discharged. The highest dissolved ozone concentration was recorded when the injected air flow rate was 5 L/min. At a discharge power of 40W as compared to 70W, the dissolved ozone was approximately 2.7 - 6.5 times higher. In regards to phenol degradation, the final degradation rate was highest at about 74.06%, when the initial pH was 10. At a discharged power of 40W, the rate of phenol decomposition was observed to be approximately 1.25 times higher compared to when the discharged power was 70W. It was established that the phenol degradation reaction was a primary reaction, and when the discharge power was 40W as opposed to 70W, the reaction rate constant(k) was approximately 1.72 times higher.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.343-346
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• 1998

Degradation characteristics of the Pr-based ZnO varistor with $Y_2O_3$content (0.0-4.0 mol!%j were investigated. It was appeared that the variation of the J-E characteristics in the reverse direction before and after the applied stress with increasing $Y_2O_3$ content was larger than that of the forward direction but the variation was extrernly small. For all varistor, the leakage current with the stress time during the applied stress somewhat increased initialy but afterthat was almost constant or slightly decreased. The overall varistor voltage and nonlinear coefficient were less than 5%. Especially, in the case of Pr-based ZnO varistor containing 2.0 mol% to 4.0 mol% $Y_2O_3$, the variation of breakdown voltage and nonlinear coefficient was less than 1% and 5%. respectively. As a result, they showed good stability.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.47 no.6
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• pp.66-72
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• 2015

This study was conducted to investigate the effects of optical brightening agents (OBA) on the chemical degradation characteristics of paper cellulose during humid heating aging. Three different types of OBAs were applied to a filter paper by dipping it in OBA solutions whose concentrations were controlled to 1% and 2%. The filter papers with an OBA were artificially aged at $80^{\circ}C$ and 65% RH, and the changes in pH of paper and viscosity of cellulose were evaluated. Their functional groups were also analyzed by ATR-FTIR (at-tenuated total reflectance fourier transform infrared spectroscopy). It was found that OBAs influenced the chemical degradation of paper cellulose during humid heating aging. Higher concentration of OBA solutions accelerated the degradation of paper cellulose. Especially, after aging for 12 days, the paper cellulose treated with the tetra-type OBA were the most significantly aged among the three types of OBAs. It was assumed that pH of OBA solutions affected the aging characteristics.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.6
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• pp.996-1003
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• 2001

In order to investigate the fatigue fracture characteristics by corrosion degradation of 12Cr alloy steel, both the fatigue characteristics in air of them artificially degraded during long period and the corrosion fatigue characteristics were experimentally evaluated in various environments which were determined from electro-chemical polarization tests. And also, their fracture mechanisms were analyzed and compared, fractographyically. From their results, the fracture mechanical characteristics of it artificially degraded during long period in the distilled water, 3.5 wt.% NaCl solution and 12.7wt.%(1M) Na$_2$SO$_4$solution of 25, 60 and 90$\^{C}$ did not show distinguishable difference comparing with non-corroded one in regardless of temperature and degradation period. It means that degradation of the material by just surface corrosion does not remarkably affect to fatigue crack growth. On the other hand, the crack growth rates by corrosion fatigue increased due to activity increase of corrosive factors such as OH(sub)-,Cl(sup)- and SO$_4$(sup)- at the crack tip with temperature increase. Therefore, the crack growth rates by corrosion fatigue were more faster than that in air of the artificially degraded specimen due to the such difference of crack growth mechanism.

• Polymer(Korea)
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• v.31 no.4
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• pp.278-282
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• 2007

The degradation characteristics of perfluoropolyether (PFPE) for computer hard disk drive have been investigated. Thermal degradation in PFPE started at $170\;^{\circ}C$ and it was completed at $450\;^{\circ}C$. If PFPE was contacted with wear fragment from slider made by $Al_2O_3{\cdot}TiC$, the thermal degradation was accelerated by the catalytic Lewis acid degradation. The Lewis acid degradation mainly took placed in methylene oride(fluoride) chain scission as well as methylene(fluoride) and hydroxy end chain. As a result, the degradation reaction accomplished as early as at $300\;^{\circ}C$. The photo oxidation due to UV exposure on PFPE caused the chain scission in methylene(fluoride), and end chain in PFPE without chain scission in methylene oxide(fluoride) and then the molecular weight of PFPE increased by expected secondary reactions between formed radicals in the photo oxidation.

• Journal of Applied Reliability
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• v.16 no.4
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• pp.356-363
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• 2016

Purpose: The purpose of this study is to propose efficiency of equipment testing the luminance degradation of OLED. Methods: The degradation model of Exponential model and Stretched exponential model is analyzed by goodness of fit test using calculated R-square. The degradation model having the higher R-square is finally selected. Scale parameter and Shape parameter using the selected degradation model is estimated. The activation energy and current density n using peck model among the accelerated model is estimated. the estimated parameters are analyzed by t-test. Results: The results of t-test show that the estimated parameters on chamber and hotplate are equal statistically. we can know the similarity of the luminance degradation rate and degradation pattern on chamber and hotplate. Conclusion: The result of the degradation test on chamber and hotplate is similar. when the accelerated degradation test on the panel of the OLED TV is performed, hotplate is requiring less samples, time and cost than chamber. so the accelerated degradation test on the panel of the OLED TV using the hoplate is efficient of time and cost.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2002.12a
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• pp.158-161
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• 2002

Many methods were proposed for insulation degradation diagnosis to High voltage and capacity Transformer in live. IDD is difficult by those methods because insulation degradation circumstances and characteristics of electrical plant are different with other Therefore, it is necessary to design diagnosis algorithms fitting for each. In this paper, We develop IIDS that used diagnosis algorithm with fuzzy model and hardware with MCU.

• KSBB Journal
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• v.14 no.2
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• pp.136-140
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• 1999

Characteristics of organic acid degradation by isolated yeast strain was investigated. Optimum initial pH was 5. Increase in cell mass was proportional to the decrease in organic acid degradation. Also no accumulation of byproduct was observed during degradation. Acetic acid degraded fast, followed by butyric acid and propionic acid in order. No significant substrate inhibition was observed up to 12 g/L of acetic acid 7 g/L of propionic acid, respectively. However, inhibition of butyric acid was significant above 4 g/L. Cell mass yield was 0.2-0.4 g cell/g acids and decreased at high decreased at high organic acid concentration. 95% of organic acid (7.5 g/L), corresponding to 13,000 ppm, was degraded in 30-40 hours.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.10
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• pp.1688-1693
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• 2016

In this study shall investigate the influence upon the electrical property of transformer oil due to the heat among accelerated heat degradation experiment for a constant hour in the typical insulation oils of mineral base oil, silicon base oil and vegetable oil. In addition, the electric insulation performance of insulation materials in transformer shall be evaluated through the electric property analysis according to the heat degradation of epoxy insulation material, which has been used for electric facilities such as a molded transformer.