• The Journal of the Acoustical Society of Korea
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• v.20 no.4
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• pp.62-70
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• 2001

Based on the recently developed resonance scattering theory for elastic waves, a relationship between the stress components, which may be measured using ultrasonic transducers, of partial waves scattered from cylindrical fluid scatterer, cavity, and resonance scatterer has been derived. The computed resonance scattered stresses exhibit frequency behaviors similar to the corresponding scattering coefficients: particularly, abrupt changes in phase by 180°near the resonant frequencies. By studying the behavior of pressure in the fluid scatterer, the physics of the theory has been further understood. Using the method studied and developed in this paper, nondestructive characterization of fluid inclusions in elastic media is expected to become more reliable.

• Journal of Korea Foundry Society
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• v.26 no.4
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• pp.184-190
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• 2006

Presence of inclusions in Ti castings imparts detrimental effects on the mechanical performance of castings. However, actual inclusions do not occur very frequently and they are difficult to locate. As a result, acquirement of specimens for mechanical tests and thus in-depth research of the adverse influence of inclusions are challenging. To address this problem, artificial inclusion seeding methodology is developed to emulate actual inclusions in Ti investment castings. Firstly, to validate that this new methodology does not result in inherent mechanical property degradation, Ti specimens with machined, backfilled and HIPed holes are produced and compared to control (unaltered), cast Ti material. Fatigue test results indicate that this 'machine-and-HIP methodology without seeding' does not result in any fundamental mechanical property alteration, which would bias ensuing comparative results. Secondly, based on this result, validation of the artificially seeded inclusions being equivalent to 'as cast' inclusions is performed by comparing their fatigue behaviors. Test specimens created by the novel artificial inclusion seeding methodology are equivalent to Ti casting specimens containing actual cast-in inclusions, and an adverse effect of inclusions in investment castings is confirmed.

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.2
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• pp.89-99
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• 1997

Although discontinuously reinforced metal matrix composite(MMC) is one of the most promising materials for applications of aerospace, automotive industries, the thermal residual stresses developed in the MMC due to the mismatch in coefficients of thermal expansion between the matrix and the fiber under a temperature change has been pointed out as one of the serious problem in practical applications. There are very limited nondestructive techniques to measure the residual stress of composite materials. However, many difficulties have been reported in their applications. Therefore it is important to establish analytical model to evaluate the thermal residual stress of MMC for practical engineering application. In this study, an elastic model is developed to predict the average thermal residual stresses in the matrix and fiber of a misoriented short fiber composite. The thermal residual stresses are induced by the mismatch in the coefficient of the thermal expansion of the matrix and fiber when the composite is subjected to a uniform temperature change. The model considers two-dimensional in-plane fiber misorientation. The analytical formulation of the model is based on Eshelby's equivalent inclusion method and is unique in that it is able to account for interactions among fibers. This model is more general than past models to investigate the effect of parameters which might influence thermal residual stress in composites. The present model is to investigate the effects of fiber volume fraction, distribution type, distribution cut-off angle, and aspect ratio on thermal residual stress for in-plane fiber misorientation. Fiber volume fraction, aspect ratio, and distribution cut-off angle are shown to have more significant effects on the magnitude of the thermal residual stresses than fiber distribution type for in-plane misorientation.

• Journal of the Korean Magnetics Society
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• v.10 no.5
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• pp.225-231
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• 2000

The crystallographic and magnetic properties of the sample F $e_{0.8}$ $Co_{0.18}$(BN)$_{0.02}$ synthesized by microwave arc-melting with the maximum power of 3.5 kW have been studied by the methods of an X-ray diffraction and the measurement of the magnetic hysteresis using the vibrating sample magnetometer at room temperature. The samples were prepared in a form of pellet pressed under the pressure of 9,000 N/c $m^2$, rolled coldly, and treated with the different temperatures. The X-ray diffraction pattern of pelleted sample shows that the crystal structure of the sample is bcc as same as that of Fe with a good uniformity. The X-ray diffraction pattern shows that a residual stress, which exists in the sample, is eliminated by final 90$0^{\circ}C$ annealing. As rolling rate and heat treatment temperature increases, the saturation magnetization and the remanence of the samples increase whereas the coercivity of the samples shows decrease. Also the saturation magnetization and the remanence of the samples were affected by rolling rate and rolling direction than heat treatment temperature, but the coercivity of the samples was affected by rolling rate and direction as well as heat treatment temperature. This means that a domain wall motion is easy due to elimination of a residual stress and an inclusion which exists in the sample by rolling and heat treatment and a local induced-magnetization easy axis was also formed to parallel to the rolling direction due to creation of the like-atom pairs across the slip plane by rolling......

• Journal of the Korean Electrochemical Society
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• v.9 no.2
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• pp.70-76
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• 2006

Micro-droplet cell with free droplet as a micro-electrochemical technique has been limited to apply to electrochemical systems with high wetting properties such as an acidic solution and low grade stainless steels(Type 316L). By loading negative pressure to a droplet, control of droplet size, and use of hydrophobic gasket, the cell is modified to be allowed to use for electrochemical systems with high wetting properties. For giving the reliability of new cell, studies on local corrosion were conducted for three different systems-an acidic chloride solution and high chromium ferritic stainless steel, the other acidic chloride solution and type 316, and a neutral chloride solution and type 316. stainless steel. Firstly, the modified micro-droplet cell allows the anodic polarization curves in an acidic chloride solution to show the fact that the local corrosion of high chromium stainless steel near the $\alpha/\sigma$ interface is due to the Cr depleted zone. Secondly, the local anodic polarization test of type 316 L in the other acidic chloride solution can be successfully conducted in the cell. Furthermore, the local polarization curves help elucidating the corrosion of type 316 with $\delta-ferrite$ phase. Finally, the polarization curves of type 316 L in a neutral chloride solution indicates that the factor affecting the pitting corrosion resistance was inclusions rather than $\delta-ferrite$.

• Korean Journal of Heritage: History & Science
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• v.50 no.1
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• pp.4-17
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• 2017

In this research, the chemical composition of the iron artifacts from the late 6th-century to early 7thcentury Baekje remains in Gwanbuk-ri, Buyeo, specifically of the nine iron artifacts including slags, furnace walls and ingot iron excavated in the District "Na", were examined by observing their chemical compounds and microstructures. As a result, GB1 and GB6 were determined to be proto-reduction lumps whereas GB2, GB3, GB4 and GB5 were determined to be tempered slags, respectively. Also, he furnace wall GB7 were containing mullite and cristobalite, which are high temperature index minerals, The extrusion temperature was found out to be about $1200{\sim}1300^{\circ}C$, and it is most likely that the smelting temperature in the furnace was in that temperature range. GB8 ingot iron was determined to be a forged ironware. This ingot iron was an intermediary product for making ironware and its nonmetallic inclusions displayed similar microstructure and contents compared to the forged iron. Because of the existence of proto-reduction lumps and forged iron, the iron making facility located in District "Na" most likely had a small-scale iron making facility that handled iron bloom smelting and refining processes.

• Conservation Science in Museum
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• v.24
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• pp.17-36
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• 2020

This paper describes the consevation treatment of eleven bigyeokjincheolloe bomb shells that were excavated from the Joseon-period local government office and fortress of Mujang-hyeon (present-day Mujang-myeon) in Gochang in 2018. It also provides information on the production method of the shells revealed through CT scanning, gamma-ray transmission imaging, and metallographic analysis. In preparation for the special exhibition "Bigyeokjincheolloe" at the Jinju National Museum in 2019 (July 16 to August 25), contaminants were removed from the shells and their surface was reinforced during the first phase of conservation treatment. Furthermore, the closures for the shells were identified for the first time. Regarding the production of the shells, the CT scanning and gamma-ray transmission imaging identified many blowholes in the interior of the body and the use of a chaplet on the side of one shell. The side of the body proved to be relatively thinner than the top and bottom. The traces of a hole for pouring molten metal into the center of the bottom indicates that molten metal was indeed emptied into the inverted body. In the metallographic analysis of two of the bodies and one lid, cementite and pearlite structures were identified on the body, indicating that it was made by casting. The presence of the ferrite structure with a partial distribution of the pearlite along with non-metallic inclusion in the lid suggested that the lid was made by forging.

• (The) Research of the performance art and culture
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• no.23
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• pp.313-346
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• 2011

This thesis investigated basic thinking of Pansori reading text appearance. Among Pansori reading texts, it is versions include unfamiliar contents and scenes in text. They was created by writers of Pansori reading text. Why created a writers of Pansori reading text them? First, writers of Pansori reading text created new contents and scenes in order to show their knowledge. Reading texts of this feature are 28pages version Chunhyangjun belonged to Kim Kwang-sun, 87pages version Chunhyangjun belonged to Sa Jae-dong, 154pages version Chunhyangjun belonged to Hong Yun-pyo etc. This reading texts was effected on knowledge culture of Chosun later period. Second, writers of Pansori reading text created new contents and scenes in order to reenact festivities field. Reading texts of this feature are 75pages version Chunhyangjun belonged to Kyungsang university, 52pages version Chunhyangjun belonged to Keimyung university etc. the former shows story field and Pansori field, the latter shows play field of Walja. Third, writers of Pansori reading text created new contents and scenes in order to lampoon yangban authority. Reading texts of this feature are 72pages version Chunhyangjun belonged to Chungnam university and it's affiliation, 59pages version Chunhyangjun belonged to Park Sun-ho and it's affiliation etc.

• Economic and Environmental Geology
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• v.51 no.4
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• pp.323-343
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• 2018

This study defines the mineralogical, micro-textural and geochemical characteristics for the carbonate rocks and discusses the fluids that have affected the depositional environment of the Lower Makgol Formation in Seokgaejae section. Based on analysis of X-ray Diffraction (XRD), Scanning Electron Microscope-Energy Dispersive X-ray Spectrometry (SEM-EDS), Electron Probe Micro Analyzer-Wavelength Dispersive X-ray Spectrometry (EPMA-WDS) and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS), carbonate miorofacies in the basal and the lower members of the Makgol Formation are distinguished and classified into four types. Type 1 dolomite (xenotopic interlocking texture) and Type 2 dolomite (idiotopic interlocking texture) have relatively high Mg/Ca ratio, flat REE pattern, low Fe and Mn. Extensively interlocking textures in these dolomites indicate constant supply of Mg ion from hypersaline brine. Type 3 and Type 4 dolomite (scattered and loosely-aggregated texture) have relatively moderate Mg/Ca ratio, MREE enriched pattern, low to high Fe and Mn. These partial dolomitization indicate limited supply of Mg ion under the influx of meteoric water with seawater. Also, the evidence of Fe-bearing minerals, recrystallization and relatively high Fe and Mn in Type 4 indicates the influence of secondary diagenetic fluids under suboxic conditions. Integrating geochemical data with mineralogical and micro-textural evidence, the discrepancy between the basal and the lower members of the Makgol Formation indicates different sedimentary environment. It suggest that hypersaline brine have an influence on the basal member, while mixing meteoric water with seawater have an effect on the lower member of the Makgol Formation.

• Composites Research
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• v.18 no.5
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• pp.21-26
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• 2005

The validity of Eshelby-type model with Mori-Tanaka's mean field theory to predict the effective material properties of composites have been investigated in terms of filler size and its arrangement. The 2-dimensional plate composites including constant volume fraction of fillers are used as the model composite for the analytical studies, where the filler size and its arrangement are considered as parameters. The exact effective material properties of the composites are computed by finite element analysis(FEA), which are compared with effective material properties from the Eshelby-type model. Although the fillers are periodically or randomly arranged, the average Young's moduli by Eshelby-type model and FEA are in good agreement, specially for the ratio of specimen size to filler size being smaller than 0.03. However, Poisson's ratio of the composite by the Eshelby-type model is overestimated by $20\%$.