• Proceedings of the KSME Conference
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• 2001.11a
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• pp.129-136
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• 2001

The remaining life estimation for the aged components in power plants as well as chemical plants are very important beacuse mechanical properties of the components are degraded with time of service exposure in high temperature. Since it is difficult to take specimens from the operating components to evaluate mechanical properties of components, nondestructive techniques are needed to estimate the degradation. In this study, test materials with 4 different degradation levels were prepared by isothermal aging heat treatment at $630^{\circ}C$. And the DC potential drop method and destructive methods such as tensile, $K_{IC}$ and hardness tests were used in order to evaluate the degradation of 1Cr-1Mo-0.25V steels. The objective of this study is to investigate the possibility of the application of DCPD method to estimate the material degradation, and to analyse the relationship between the electrical resistivity and the degree of material degradation.

• Journal of Industrial Technology
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• v.35
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• pp.47-53
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• 2015

Recent extreme weather events and natural disasters are causing rapid aging of the ancient structures with cultural value. It has threatened the safety and management. The construction design documents are not kept for such long time. Even if they are, they seem to be mismatched with the design structures due to corrosive effects. For these reasons, Korea has been facing difficulties in maintenance, reengineering and safety evaluation. In this study, three dimensional point cloud surface of bobsleigh is obtained using 3D LiDAR scanner. The obtained structure is compared with the original design and found to be highly accurate. The study shows the application of reverse engineering technique and its potential use for other civil structures.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.10a
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• pp.25-28
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• 2000

In this paper, the technology for accelerating degradation & life estimation on the traction motor was introduced with the stator form-winding sample coils of the 200 Class insulation system The accelerative degradation was performed in 10 cycles, which were composed of thermal stress, fast rising surge voltage, vibration, water immersion and overvoltage applying. After aging of 10 cycles, condition diagnosis test such as insulation resistance & polarization index, capacitance & dielectric loss and partial discharge properties were investigated in the temperature range of $20{\sim}160^{\circ}C$. Relationship between degradation conditions and diagnosis results were analyzed to find an dominative degradation factor at the end-life point

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1992.11a
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• pp.128-131
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• 1992

In this paper, the skewness properties of partial discharge at interface layer in mica-epoxy composite material were investigated and studied on interface specimens which has internal electrodes. As a result, it has been confirmed that the interface exists as abnormal resin layer and the contact condition at the interface is depended upon the density of si lane aqueous solution. The Pulse frequency of discharge at abnormal interface has been shown a linear increasing with enlargement of discharge quantity according to rising of the applied voltage. Whereas, in case of normal interface, pulse frequency represented exponential increasing at the saturating point of discharge quantity. The aging model can be represented from the variable characteristics of skewness.

• Journal of Surface Science and Engineering
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• v.23 no.1
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• pp.44-51
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• 1990

Effects of temperature on the tensile properties of annealed and hydirded Zircaloy-4 plate in which hydrides are precitated paralled to the rolling direction were investigated. The main results obtained are as follows : 1) In annealed Zircaloy-4, yield point phenomenon was found in the temperature range of $200-550^{\circ}C$, while in hydrided alloy the phenomenon was found in the range of $200-400^{\circ}C$. 2) The dynamic strain aging behavior was occurd in the temperature interval of 400-$550^{\circ}C$in both annealed and hydrided Zircaloy-4. 3) The nearly values of yield strength, tensile stength and elongation are obtained in both annealed and hydried Zircaloy-4. From this result, we are led to conclude that the hydrides which are preiptated parallel to the circumferenial direction of nucler fuel are not so harmful for tensile properties of the clad.

• Journal of Pharmaceutical Investigation
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• v.6 no.2
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• pp.95-100
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• 1976

A study on the effect of the pH of precipitation on the acid consuming capacity, aging stability, physical and chemical properties of hydrous aluminum oxide prepared by the reaction of aluminum chloride and ammonium hydroxide solution was carried out by means of X-ray diffraction, IR spectra and differential thermal analysis. The results from these experiments are as follows: 1. Hydrous aluminum oxide precipitated at lower pH showed better acid consuming capacity, higher stability and more anion contained in the structure than that prepared at higher pH. 2. The hydrous aluminum oxide prepared at lower pH is amorphous and that prepared at higher pH is crystalline hydrated hydrous aluminum oxide, i.e., Bayerite and these results are conformed to Rhee's hypothesis. 3. The rate of loss of reactivity and the end-point reactivity are related to the pH of precipitation.

• Journal of the Korean Society for Heat Treatment
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• v.7 no.3
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• pp.160-168
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• 1994

This was studied about mechanical characteristic of AC4A/SiCw 10-30% reinforced composites. Tensile strength of pressed base metal(base metal) with SiCw preform was higher than without pressed base metal(AC4A). If SiCw whisker volume fraction was increased, tensile strength at room temperature was increased. And tensile strength of SiCw 30% was about $35kg/mm^2$. Tensile strength of SiCw 30 % $400^{\circ}C$ at same time aging was the most excellence, about $40kg/mm^2$. The fracture energy value of composite material at three point bending test was higher than AC4A. Dislocation at matrix of composite material was evenly distributed. But dislocation around whisker of composite material was more existed than matrix. The reasom was thought of pile-up around whisker.

• Journal of the Korea Institute of Building Construction
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• v.13 no.1
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• pp.20-28
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• 2013

Flexure toughness of Steel Fiber Reinforced Concrete (SFRC) shows a time-dependent characteristic due to the hydration process of the cement matrix in the SFRC system. The effect of two important factors, water/cement (w/c) ratio and fiber volume fraction, on the flexure toughness development of SFRC were investigated. Three different SFRC mixtures with hooked-end steel fibers were tested using a four-point bending testing configuration. Each mixture was tested at five different ages. The results showed that the post-peak toughness of SFRC developed at an earlier age than the first-crack toughness.

• Proceedings of the KIEE Conference
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• 1997.07c
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• pp.1052-1055
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• 1997

The importance of dynamic stability of power system is increasing as the excitation system using static type are greatly enlarged. There are several types of PSS at Present, Elements of PSS consist of Notch filter, lead-lag filter, washout limiter which are variable. The existing power system has a difficulty in determining the optimal PSS parameters whenever PSS is installed. And it is recommended to retune PSS parameters periodically because system characteristics change due to aging. In this paper, intelligent PSS using fuzzy concept is introduced to get over difficulties mentioned above. The usefulness of fuzzy-type PSS was verified by applying FPSS to KEPCO power system. Generally, the voltage regulation deteriorates if conventional PSS is applied because supplementary signal is added into AVR summing point to damp Power oscillation. In this paper this problem is solved by AVR limiter and fuzzy members tuning.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1995.10a
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• pp.85-95
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• 1995

This paper describes a diagnosis of transformer by ultrasonic signal due to partial discharge. The ultrasonic signal can be measured when partial discharge is generated in a real transformer. The trend of partial discharge in transformer was estimated by counting the number of ultrasonic signals until insulation paper in the point-to-plane electrode is destroyed. The number of ultrasonic signals is closely related to the number of the electrical signals by partial discharge. The trend of the ultrasonic signal number could easily be distinguished by taking moving average.