• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.10
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• pp.1201-1206
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• 2013

Defects that occur during the manufacturing process or operation of a wind turbine blade have a great influence on its life and safety. Typically, defects such as delamination, pore, wrinkle and matrix crack are found in a blade. In this study, the detectability of the pores, a type of defect that frequently occur during manufacturing, was examined from the full field strain distribution determined with the image correlation technique. Pore defects were artificially introduced in four-ply laminated GFRP composites with $0^{\circ}/{\pm}45^{\circ}$ fiber direction. The artificial pores were introduced in consideration of their size and location. Three different-sized pores with diameter of 1, 2 and 3 mm were located on the top and bottom surface and embedded. By applying static loads of 0-200 MPa, the strain distributions over the specimen with the pore defects were determined using image correlation technique. It was found the pores with diameter exceeding 2 mm can be detected in diameter.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.412-423
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• 2000

By using the relation between stress intensity factor and AE parameter, new approach method for assessing the crack length and detectability of crack was proposed. Laboratory experiment was carried out to identify AE characteristics of fatigue cracks for compact tension specimen. The relationship between a stress intensity factor and AE signals activity as well as conventional AE parameter analysis was discussed. As a result, the features of specific parameter such as the length of crack growth the AE energy, the AE peak amplitude, and the cumulative AE hits, showed the almost same trend in their increase as the number of fatigue cycle increased. From the comparisons of peak amplitude and AE energy with stress intensity factor, it was verified that the higher stress intensity factors generated AE signals with higher peak amplitude and a larger number of AE counts. If we can get more reliable database for the relation between AE parameters and stress intensity factor, this approach will provide a good information for evaluating both the existence of crack and the minimum detectable size of crack.

• Fire Science and Engineering
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• v.22 no.5
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• pp.72-78
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• 2008

The mass loss rate and heat release rate of EPS sandwich panel cores were analysed using variable external irradiation level. The experimental materials were exposed to incident heat fluxes form 20 to 50 kW/$m^2$. For the measurement of mass loss rate and heat release rate, the size of specimen was $100mm{\times}100mm{\times}50mm$ and the samples were 3 different kinds. The combustion heat were carried out from the Oxygen bomb calorimeter and the mass loss rate and heat release rate were carried out from the Mass loss calorimeter according to ISO 5660-1. As the results of this study, the mass loss rate of Type A, B, and C were 2.7 g/$m^2s$, 2.8 g/$m^2s$, and 2.3 g/$m^2s$ and the heat release rate of Type A, B, and C were 58.23 kW/$m^2$, 47.19 kW/$m^2$, and 50.06 kW/$m^2$ respectively at the heat flux of 50 kW/$m^2$. In conclusion, when the heat release characteristics applied to a classification system of Canada, Type A and C can be classified grade C-3, and Type C can be classified grade C-2 from all data of this study.

• Korean Journal of Materials Research
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• v.7 no.1
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• pp.40-49
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• 1997

$Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ thermoelectric matcrials havc 11et:n fahricxted hy mechanical alloying and hot pressing methods. Microstructure and thermoelectric properties of the hot 11resseii $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ have been investigated Lvith variations of hot pressing temperature and dopmt atltiition Formation of $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ alloy powders was completed by mechanical alloying of the as-mixed Ri. Te, arid Sc grmules of ~3.6mm size for 3 hours at ball-to-material weight ratio of 5 : 1. Figure of merit of $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ was markedly incrcwieti hy hot pressing at temperatures above $450^{\circ}C$, and value of $1.9{\times}10^{-3}/K$ was obtained for the specimen hot pressed at $550^{\circ}C$. With addition of 0.015 wt% Ri as acceptor dopant, figure of merit ol $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ hot pressed $550^{\circ}C$$2.1{\times}10^{-3}/K$.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.6
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• pp.21-30
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• 2013

As increasing number of large-size earthquake, the social interest of seismic retrofitting of RC structure is growing. Especially, the RC columns that are not reflected seismic design can not resist lateral loads by the earthquake. The brittle fracture of Non-seismic designed columns lead to full collapse of the building. Thus, the emergency columns reinforcement method is needed. That have a fast construction time, do not cause damage to the column. In the past, cross-sectional expansion method, a steel plate reinforcing method is applied mainly, but in recent years, carbon fiber sheet taking advantage of FRP (Fiber Reinforced Polymer) is widely used. In this study, retrofitting effect of seismic performance of FRP seismic reinforcement, which is possible to emergency construction, was examined. Reinforced concrete specimens were constructed to experimental study. The seismic performence of specimes retrifitted with FRP seismic reinforcement were evaluated. As a result, the seismic performance of specimen reinforced with FRP seismic reinforcement has been improved.

• Applied Chemistry for Engineering
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• v.25 no.4
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• pp.380-385
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• 2014

Spherical atomizing reduction steel slag was prepared by atomizing technology using reduction steel slag (ladle furnace slag, LFS) generated from steel industry. In order to develop the mass-recycling technology of atomizing reduction steel slag, polymer concrete composite was prepared using spherical atomizing reduction steel slag instead of fine aggregate (river sand) and coarse aggregate (crushed aggregate), depending on the grain size. Different polymer concrete specimens were prepared with the various proportions of polymer binder and replacement ratios of atomizing reduction steel slag in order to investigate the characteristics of polymer concrete composite. Results showed that compressive strengths of polymer concrete specimens decreased with the increase of replacement ratios of atomizing reduction steel slag, but flexural strengths of the specimens showed a maximum strength at the 50% of replacement ratios of atomizing reduction steel slag. It was concluded that addition ratio of polymer binder, which affect greatly on the prime cost of production of polymer concrete, could be reduced by maximum 18.2 vol% because the workability of the polymer concrete was remarkably improved by using the atomizing reduction steel slag. However, further study is required because the mechanical strength of the specimen using atomizing reduction steel slag was greatly reduced in hot water resistance test.

• Journal of the Korean Geosynthetics Society
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• v.11 no.2
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• pp.31-38
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• 2012

The recycled aggregate for construction, slag, coal ash and such may elute leachates by chemical reaction when in touch with water, and to confirm this, generally the waste process test is executed. If the test result criteria are met, it can be used as replacement aggregate. In case of steel slag, however, the chemical reaction does not end in a short term, but occurs over a long time, generating eluted leachate. Thus, in this study, the leachate from steel slag were analyzed for heavy metal, and the pH change and environmental characteristics of eluted leachate were analyzed. According to the experiment result, the chemical reaction of free CaO and water within the steel slag occurred more actively when stirred, and the smaller the grain size, the higher the pH was. As the result of waste process test, all test items for the two types of specimen were found to have no heavy metal, but from the ICP test analysis result, heavy metals such as Al, Pb, Zn, Fe were detected. It could be confirmed that chemical reaction would occur upon contact of steel slag and water, and heavy metal may be detected depending on experiment conditions and analysis methods, the long-term environmental characteristics should be examined for utilization of steel slag.

• Journal of Conservation Science
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• v.28 no.1
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• pp.29-37
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• 2012

This study discusses a mercury amalgam gilding technique and examines how the color, surface and section of the gilt layer changes as the condition of heat treatment with mercury amalgam gilt object is changed. Some previous studies have mentioned reasons for various colors on gilt bronze artifacts depending on gilding manufacture and environment. However, reason for reddish color with gold on the artifacts' surface brought on high temperature corrosion has yet to be discussed and analyzed. A methodology was found in representing the mercury amalgam gilding technique and heat treatment test. According to the result of the heat treatment test, in the conditions of higher temperature and longer time, the oxidized layer on the gilt layer was distributed more widely and in the part when the oxide layer was eliminated, the gilt layer with a reddish color was observed. Moreover, in the surface observation of the specimen on which yellow and reddish colors were agitated, the changing aspects of its surface condition differed by colors. When investigated the section, it was observed that the void density and size became larger. After a test, the surface components changed; the temperature of heat treatment increased, component ratio of Hg and Au decreased gradually but component ratio of Cu increased. In regard to the gilt layer, as the time was longer and the temperature became higher for the heat treatment, the component ratio of Au and Cu by layers tended to change in inverse proportion. It is concluded that gilding techniques and the burial environment can make a difference in the surface color of the gilt layer on the gilt bronze artifacts, the high temperature corrosion that occurs by heat after they are manufactured is also one of the factors that affects their surface color.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.4
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• pp.18-25
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• 2020

The purpose of this study is to investigate the mechanical and carbon-capture properties of foam concrete containing stainless steel argon oxygen decarbonization(AOD) slag. AOD slag was used as a binder, and foam concrete having a foaming ratio of 69 ± 0.5 % and a slurry density of 573.2 to 578.6 kg / ㎥ was produced. In order to examine the effect of carbonation, blended specimen was cured by two types : normal curing and CO₂ curing. As a result of the experiment, the specimens incorporating AOD slag showed higher compressive strength than Plain after CO₂ curing. According to the analysis of the image of foam concrete, it was confirmed that the ST30 has a lower total pore volume and average pore size than plain, resulting in high compressive strength. The SEM analysis confirmed the formation of calcite by carbonation of AOD slag. Through the thermogravimetric analysis, the increase of CO₂ uptake was confirmed by the incorporation of AOD slag. Foam concrete has a higher porosity than normal concrete, so it is expected that carbon-capture performance can be improved by using a AOD slag.

• Restorative Dentistry and Endodontics
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• v.31 no.6
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• pp.470-476
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• 2006

The objective of this in situ study was to evaluate the effects of whitening strip (Claren, LG Household & Health Care Ltd, 2.6% hydrogen peroxide) and gel (Opalescence, Ultradent, 10% carbamide peroxide) on microhardness of enamel in comparison with untreated control. Extracted twenty human upper incisors were disinfected, cleaned, and labial side of each incisor sectioned into 3 fragments by 2 ${\times}$ 2 mm size. After sectioning, labial sides of fragments were flattened and fixed to orthodontic bracket using flowable composite resin. Specimens prepared from each tooth were attached to the labial side of upper incisors of twenty volunteers one by one and treated by three different methods: (1) untreated control (2) treated with whitening strip for 14 days (3) treated with whitening gel for 14 days. Microhardness (Microhardness tester, Zwick) of each specimen was measured at the baseline of pre-treatment, immediate after bleaching treatment, 14 days after bleaching treatment and Knoop Hardness Number was determined. Microhardness changes of experimental groups were compared. The results show that tooth whitening strip and gel used in this study does not effect the microhardness of enamel during bleaching procedure.