• Proceedings of the KWS Conference
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• 2001.05a
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• pp.224-227
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• 2001

In this study, CT specimens were prepared hem ASTM SA516 which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at $25^{\circ}C$, -3$0^{\circ}C$, -6$0^{\circ}C$, -8$0^{\circ}C$, -l$0^{\circ}C$ and -l2$0^{\circ}C$ and in the range of stress ratio of 0.1, 0.3 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range $\Delta K_{th}$ in the early stage of fatigue crack growth ( Region I ) and stress intensity factor range $\Delta$K in the stable of fatigue crack growth ( Region II) was increased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da/dN - $\Delta$K in Region II, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It assumed that the fatigue crack growth rate da/dN is rapid in proportion to descend temperature in Region H and the cryogenic-brittleness greatly affect a material with decreasing temperature.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.387-392
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• 2005

For the production of further functional bio-degradable plastic(polybutylene succinate:PBS) with $TiO_{2}$ as photocatalyst, which shows the decomposition of detrimental organic compound and pollutant under ultraviolet irradiation, we attempted to prepare $TiO_{2}$ coatings on PBS substrate by HVOF and plasma spraying techniques under various conditions. The microstructures of coatings were characterized with SEM and XRD analysis, and the photocatalytic efficiency of coatings was evaluated through the photo degradation of gaseous acetaldehyde. The effects of primary particle size and spraying parameters on the formation behavior, photo catalytic performance and mechanical characteristics of the coatings have been investigated. The results indicated that with respect to both the HVOF sprayed $P_{200}$ and $P_{30}$ coatings, the high anatase ratio off 100% can be achieved regardless of fuel gas pressure. On the other hand, the HVOF sprayed $P_{7}$ coating exhibited largely decreased anatase ratio (from 100% to 49.1%) with increasing the fuel gas pressure, which may be attributed to the much higher susceptibility to heat of 7nm agglomerated powder. In terms of photocatalytic efficiency, HVOF sprayed $P_{200}$ and $P_{30}$ coatings seem to predominate as compared to that of plasma sprayed $P_{200}$ coatings owing to the higher anatase ratio. However, the HVOF sprayed $P_{7}$ coatings didn't show the photo catalytic activity, which may result from the extremely small reaction surface area to the photo-catalytic activity and low anatase ratio. Such functional PBS with new roles is expected to cosiderably contribute to the reduction of aggravated environmel problem.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.6 no.2
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• pp.20-27
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• 2010

In order to prevent the corrosion of component contacted primary water designed alloy 600 material in the nuclear power plant. But the primary water stress corrosion cracking(PWSCC) of alloy 600 and weld area occurs continuously due to the residual stress. The leakage accident resulted from PWSCC in the drain nozzle of the steam generator of domestic power plants. Heater sleeves of the pressurizer are welded with alloy 600 weld material and therefore exposed to the primary water environment. PWSCC occurred in heater sleeve material and weld area of many foreign power plants. The current issue of domestic nuclear power plants are consequently concentrated to PWSCC of similar material. In order to improve the detection and the sizing of the PWSCC in the welding sleeve of the pressurizer, the automatic UT system and multi-directions probe sets have been developed. The experimental studies have been performed using the mock-up block containing artificial reflectors(ID connected EDM notch) and semi-artificial cracks made from thermal fatigue. The automatic UT System is applied in the detection and the length sizing of the ID/OD on the tube and the J-groove weld area of the artificial reflectors and results of the detection and the sizing are compared respectively. Also, the developed automatic UT system is successfully accomplished to inspect the heater sleeve and the J-groove weld area on the pressurizer for the detection of PWSCC.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.4
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• pp.75-82
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• 2001

Static loadings on ship structure induced either by water pressure before service such as a tank test and ballasting or by cargo pressure during first laden voyage cause relatively much greater stress than dynamic loadings induced by wave. With these static pre-loadings, the initial residual stresses around welded joint, where fatigue strength is concerned(in most cases, where stress concentration occurs) are expected to be shaken-down in a great extent by the elasto-plastic deformation behavior of material. Therefore, it is more resonable to assess the fatigue strength of ship structure with S-N data which have taken into account the effect of shaken-down residual stresses(re-distributed stresses) on the fatigue strength. In this research work, the re-distribution of residual stresses by the tensile pre-loading is measured using an ordinary sectioning method for specimens of padding plate weldment. Fatigue tests are performed also to evaluate the fatigue strength of the both as-welded and pre-loaded specimens.

• Composites Research
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• v.36 no.6
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• pp.422-428
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• 2023

The electrical contact resistance between the bipolar plate (BP) and the carbon felt electrode (CFE), which are in contact by the stack clamping pressure, has a great impact on the stack efficiency because of the relatively low clamping pressure of the vanadium redox flow battery (VRFB) stack. In this study, a polyethylene (PE) composite-CFE hybrid bipolar plate structure is developed through a local heat welding process to reduce such contact resistance and improve cell performance. The PE matrix of the carbon fiber composite BP is locally melted to create a direct contact structure between the carbon fibers of CFE and the carbon fibers of BP, thereby reducing the electrical contact resistance. Area specific resistance (ASR) and gas permeability are measured to evaluate the performance of the PE composite-CFE hybrid bipolar plate. In addition, an acid aging test is performed to measure stack reliability. Finally, a VFRB unit cell charge/discharge test is performed to compare and analyze the performance of the developed PE composite-CFE hybrid BP and the conventional BP.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.20 no.1
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• pp.25-31
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• 2024

The core shroud of rector vessel internals (RVI) of OPR1000 and ARP1400 is made of Type 304 stainless steel (SS) by bending and welding process that may induce high deformation and residual stress in manufacturing. This work aims to evaluate the susceptibility of stress corrosion crack (SCC) initiation of bent parts of RVI in high temperature primary water environment. For SCC initiation test, tensile specimens were fabricated from the 90 degree bent plate of Type 304 SS (DT specimen), that is an archived part of a Korean APR1400. After the SCC initiation test, the specimen surface was thoroughly examined by optical and scanning electron microscopy, and compared to the specimen fabricated from the as-received plate of Type 304 SS (AR specimen). The surface observation revealed that SCC initiated on the AR specimen surface in typical intergranular (IG) mode, while SCC on the DT specimen occurred in transgrannular mode as well as IG mode. It was also found that the size and number of SCC on the DT specimen were larger than that on the AR specimen. This was attributable to a strain-hardening during the bending process. To compare the susceptibility of SCC initiation, total crack density (TCD) was calculated from the total crack length divided by the measured area of AR and DT specimens. TCD of DT specimen was 4.6 times higher than AR specimen in average, indicating that higher possibility of degradation of bent parts of RVI for a long-term operation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.5
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• pp.109-115
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• 2008

As structures are getting super-rise and large-sized, introducing the construction methods such as prefabrication of bar-meshes and complex method are being actively discussed to pursue the high quality of reinforced concrete, the simplification of field works, and the reduction of duration, as well as the study on how to connect reinforcing rods, which occurs while applying the same methods, is in progress Also, the pressure welded joint is a kind of method that heats the ends of reinforced bars locally and joint them, and after the pressure welding, the vulnerable part in the reinforced bar occur. Thus, in the construction field, the throughout quality control is necessary because of the delayed duration and the lowered construct ability. In this study, of the traditional lap splice method and the mechanical splice one, the screw coupler, we tried to look into through experiments the prefabrication method of bar-meshes, a typical joint method usually used for the joint parts for PSC structures applying the reinforced bar with its big diameter, and a newly-developed up-set coupler method. And we also examined the characteristic of tensile.

• Journal of the Korean Institute of Gas
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• v.14 no.5
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• pp.13-18
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• 2010

This paper presents the development of an integrated control and safety management system for 9% nickel steel LNG storage tank. The new system added the measuring equipment of pressure, displacement and force compared to the conventional measurement and control system. The measured data has simultaneously been processed by integrating and analyzing with new control equipments and safety management systems. The integrated control and safety management system, which may increase a safety and efficiency of a super-large full containment LNG storage tank, added additional pressure gauges and new displacement/force sensors at the outer side wall and a welding zone of a stiffener and top girder of an inner tank, and the inner side wall of a corner protection tank. The displacement and force sensors may provide failure clues of 9% nickel steel structures such as an inner tank and a corner protection, and a LNG leakage from the inner tank. The conventional leak sensor may not provide proper information on 9% nickel steel tank fracture even though LNG is leaked until the leak detector, which is placed at the insulation area between an inner tank and a corner protection tank, sends a warning signal. Thus, the new integrated control and safety management system is to collect and analyze the temperature, pressure, displacement, force, and LNG density, which are related to the tank system safety and leakage control from the inner tank. The digital data are also measured from control systems such as displacement and force of 9% nickel steel tank safety, LNG level and density, cool-down process, leakage, and pressure controls.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.5
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• pp.713-723
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• 2003

In this study, a state of art review of existing residual stress analysis techniques and representative solutions is presented in order to develope the residual stress analysis procedure for fitness-for-service (FFS) assessment of welded structure. Critical issues associated with existing residual stress solutions and their treatments in performing FFS are discussed. It should be recognized that detailed residual stress evolution is an extremely complicated phenomenon that typically involves material-specific ther-momechanical/metallurgical response, welding process physics, and structural interactions within a component being welded. As a result, computational procedures can vary significantly from highly complicated numerical techniques intended only to elucidate a small part of the process physics to cost-effective procedures that are deemed adequate for capturing some of the important features in a final residual stress distribution. Residual stress analysis procedure for FFS purposes belongs to the latter category. With this in mind, both residual stress analysis techniques and their adequacy for FFS are assessed based on both literature data and analyses performed in this investigation.

• Conservation Science in Museum
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• v.13
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• pp.71-80
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• 2012

So-hwan earring(small hoop earing) is orbicular earring that have only main hoop. In this study, So-hwan earring from Baekje tombs are analyzed scientifically and those is attempted to find the correlation between scientific results and historical constituent. Six earrings were excavated from Habjung-ri sites in Buyeo and formative features and material characteristics of them were analyzed by microscope and XRF. As a results, various toreutics about producing gold silver alloy, pressure welding and amalgam plating that existed in Baekje from Ungjin period to Sabi period.