• Korean Journal of Metals and Materials
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• v.49 no.2
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• pp.104-111
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• 2011

An ultrafine grained Mg-9Al-1Zn magnesium alloy with the mean grain size less than $1{\mu}m$ was produced by using high-ratio differential speed rolling. The processed alloy exhibited excellent superplasticity at relatively low temperatures. The micro-forming tests were carried out using a micro-forging apparatus with micro V-grooved shaped dies made of silicon and the micro-formability was evaluated by means of micro-formability index, $R_f$ ($=A_f/A_g$, $A_f$: formed and inflowed area into the V-groove, $A_g$: area of the V-groove). The $R_f$ value increased with temperature up to $280^{\circ}C$ and then decreased beyond $300^{\circ}C$. The decrease of the $R_f$ value at $300^{\circ}C$ was attributed to the accelerated grain coarsening. Increasing the micro-forging pressure increased the $R_f$ values. At a given die geometry, die filling ability decreased as the die position moved away from the die center to the end. FEM simulation predicted this behavior and a method of improving this problem was proposed.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.1726-1735
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• 2008

Seoulmetro has operated the air cooling equipment for 57 stations to improve services focused on our customers who use Seoulmetro during the summer season and has established every year. However, a new set of problems has arisen with the cooling tower to support a heat exchange of cooling water. The most important matter is loss of efficiency in the cooling tower. The leading cause of this problem is that we use an indoor type. As the cooling tower room is located in the underground of the city because of the residents near the station. Therefore It is difficult to establish the cooling tower on the ground. But it is unsuitable for the location requirements of the underground type because it has a limited space to set up the air cooling equipment, for example, the cooling tower and a ventilating opening. As a result of such an unfavorable condition, the cooling tower doesn't work efficiently and the warmth of cooling water because of insufficiency of a heat exchange and a refrigerator's technical obstacle such as a high-temperature and a high-pressure has arisen. To prevent this situation, the operator tend to reduce refrigerant. Accordingly, the efficiency of the air conditioning is getting lower and lower. Study wishes to analyze the matter to improve indoor cooling tower efficiency and recommend a best practice for a person who manage the establishment.

• Corrosion Science and Technology
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• v.20 no.4
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• pp.189-195
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• 2021

A technology for designing and licensing a dedicated radiation shielding facility needs to be developed for safe and efficient operation an R&D center. Technology development is important for smooth operation of such facilities. Causes of damage to internal structures (such as baffle former bolt (BFB) of pressurized water reactor) of a nuclear power reactor should be analyzed along with prevention and countermeasures for similar cases of other plants. It is important to develop technologies that can comprehensively analyze various characteristics of internal structures of long term operated reactors. In high-temperature, high-pressure operating environment of nuclear power plants, cases of BFB cracks caused by irradiated assisted stress corrosion cracks (IASCC) have been reported overseas. The integrity of a reactor's internal structure has emerged as an important issue. Identifying the cause of the defect is requested by the Korean regulatory agency. It is also important to secure a foundation for testing technology to demonstrate the operating environment for medium-level irradiated testing materials. The demonstration testing facility can be used for research on material utilization of the plant, which might have highest fluence on the internal structure of a reactor globally.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.3
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• pp.7-13
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• 2019

Recently, an automobile market used to natural gas has emerged as fast-growing as the several countries, who holds abundant natural fuel resources, has promoted to supply the national agency for an automobile car. LNG fuel vessel is more efficient in another way as the energy density is high, but it requires a high technology and investment to maintain extreme low temperature. CNG fuel vessel are relatively low-cost alternative to LNG, but poorly economical in terms of energy density as well as showing safety issues associated with compressed pressure. The development of adsorbed natural gas (ANG) has emerged as one of potential solutions. Therefore, it is desirable to reduce the weight of vessel by applying light-weighed a composite carbon fiber in order to response to the regulation of $CO_2$ emission. Herein, this study make the prototype ANG vessel not only based on the optimal design and analysis of material characteristic but also based on the shape design, and it suggest a new type for the composite carbon fiber vessel which verified functional test. Moreover, the detail shape design is analyzed by a finite element analysis, and its verifies the ANG vessel.

• Journal of Advanced Navigation Technology
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• v.22 no.2
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• pp.90-95
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• 2018

In the solid rocket motor (SRM), a thrust of rocket is generated by a nozzle so it is very important device. The nozzle of SRM is a condition of high temperature and high pressure so occurs the erosion by combustion gas. The liquid rocket propulsion systems (LRPSs) cools the nozzle by the fuel and oxidizer but SRM does not cool the nozzle. This paper deal with the development of the oxy-acetylene torch tester and investigate the thermochemical erosion properties for the thermal insulation materials of the graphite rocket nozzle throat through the experiment. The results of experiments are compared with the results of Theoretical model and identify the key factors affecting of erosion. The results is in good agreement with the experimental data.

• Korean Journal of Metals and Materials
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• v.49 no.7
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• pp.515-521
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• 2011

Small punch creep testing has received attention due to the convenience of using smaller specimens than those of conventional uniaxial creep tests, which enables creep testing on developing or currently operational components. However, precedent studies have shown that it is necessary to consider friction between the punch and specimen when computing uniaxial equivalent stress from a finite element model. In this study, small punch creep behaviors of AISI 316L stainless steel, which is widely used in high temperature-high pressure machineries, have been compared for the two different ceramic balls such as $Si_3N_4$ and $Al_2O_3$. The optimal range of the friction coefficient is 0.4~0.5 at $650^{\circ}C$ for the best fit between experimental and simulation data of AISI 316 L stainless steel. The higher the friction coefficient, the longer the creep rupture time is. Therefore, the type of ceramic ball used must be specified for standardization of small punch creep testing.

• International Journal of Industrial Entomology and Biomaterials
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• v.46 no.1
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• pp.9-15
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• 2023

Recently, a silkworm strain (tentatively named Sericinjam) producing 100% sericin cocoons has been studied in South Korea. In this preliminary study, the crystallinity, mechanical properties, and dissolution conditions of sericin from Sericinjam cocoons were examined. The Sericinjam cocoon could be dissolved in water at high temperature (120℃) and high pressure (HTHP method) in an autoclave and in a CaCl₂/H₂O/EtOH mixture (ternary solvent method), resulting in 82% and 97% dissolution after 30 min, respectively. The solution viscosity of the silk sericin formic acid (SSFA) solution obtained from sericin extracted using the ternary solvent method was higher than that obtained using the HTHP method; however, SSFA solutions obtained from sericin extracted from conventional Baekokjam cocoons yielded a higher solution viscosity. The crystallinity and breaking strength of the sericin film from Sericinjam cocoons were slightly lower, respectively, than those from Baekokjam cocoons. In contrast, the elongation at break of the Sericinjam sericin film obtained using the HTHP method was higher than that of the Baekokjam sericin film.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.46 no.3
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• pp.101-108
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• 2023

Although the proportion of coal-fired power generation is decreasing, efficient operating technology is needed to continuously invest in facilities and reduce maintenance costs until it is abolished. Boilers, one of the main facilities of power plants, operate for a long time in harsh environments of high temperature and high pressure. In addition, damage due to deterioration is likely to occur depending on the fuel and tube material used. It is very important to judge soundness because damage caused by deterioration adversely affects facility operation. Previously, replication method was used to analyze the progress of deterioration. In the replication method, pre-treatment such as chemical treatment is performed on the boiler tube in the field, the area is reproduced by attaching a film, and the replicated film is determined by an expert in the laboratory with an expensive microscope. However, this method involves substantial costs and time requirements, as well as the possibility of human errors. To address these issues, we developed a mobile health assessment system in this research. Since it is detachable and takes images in real time, this system enables swift evaluations across a broad range and facilitates the assessment of preprocessing quality. In addition, it was intended to reduce existing human mistakes by developing a degradation classification algorithm using the merger cluster method.

• Progress in Superconductivity and Cryogenics
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• v.6 no.4
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• pp.9-12
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• 2004

We report a successful fabrication of high-$J_C$ $NdBa_2Cu_3O_{7-{\delta}}$ (NdBCO) films on (100) $SrTiO_3$ substrates by pulsed laser deposition (PLD) in high oxygen pressures ranging from 400 to 800 mTorr. Fabricated NdBCO films exhibited only c-axis orientation, good out-of-plane and in-plane textures, and also excellent superconducting properties, including critical temperature ($T_C$) and critical current density ($J_C$) of above 90 K and the highest of $3.1MA/cm^2$ at 77 K in self-field, implying that NdBCO is a perspective alternative to YBCO for coated conductor. In low oxygen pressures ranging from 100 to 200 mTorr, however, the films showed a-, c-mixed orientation and degraded $T_{C,zero}$ values due to the formation of $Nd_{1+x}Ba_{2-x}Cu_3O_{7-{\delta}}$-type solid solutions with an excessive substitution of $Nd^{3+}$ ions for the $Ba^{2+}$ sites.

• Journal of the Korean Society of Visualization
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• v.22 no.1
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• pp.18-27
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• 2024

A series of shock wave pulses with Mach number 2.2 of 100, 200, and 300 shocks were applied to lead sulfide (PbS) nanomaterials at intervals of 5 sec per shock pulse. To investigate the crystallographic, electronic, and magnetic phase stabilities, powder X-ray diffractometry (XRD), diffused reflectance spectroscopy (DRS), and vibrating-sample magnetometry (VSM) were employed. The material exhibited a rock salt structure (NaCl-type structure); XRD results indicated that material is monoclinic with space group C121 (5). Further, XRD results showed shifts due to lattice contraction and expansion when material was subjected to shock wave pulses, indicating stable material structure. Based on the data obtained, we believe that the PbS material is a good choice for high-pressure, high-temperature, and aerospace applications due to its superior shock resistance characteristics.