• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.10a
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• pp.101-102
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• 2012

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.681-682
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• 2009

• Nuclear Engineering and Technology
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• v.48 no.2
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• pp.533-544
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• 2016

This paper provides a reference to determine the seal performance of metallic O-rings for a reactor pressure vessel (RPV). A nonlinear elastic-plastic model of an O-ring was constructed by the finite element method to analyze its intrinsic properties. It is also validated by experiments on scaled samples. The effects of the compression ratio, the geometrical parameters of the O-ring, and the structure parameters of the groove on the flange are discussed in detail. The results showed that the numerical analysis of the O-ring agrees well with the experimental data, the compression ratio has an important role in the distribution and magnitude of contact stress, and a suitable gap between the sidewall and groove can improve the sealing capability of the O-ring. After the optimization of the sealing structure, some key parameters of the O-ring (i.e., compression ratio, cross-section diameter, wall thickness, sidewall gap) have been recommended for application in megakilowatt class nuclear power plants. Furthermore, air tightness and thermal cycling tests were performed to verify the rationality of the finite element method and to reliably evaluate the sealing performance of a RPV.

• Clinical Endoscopy
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• v.56 no.5
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• pp.633-649
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• 2023

Background/Aims: Mechanical properties (MPs) and axial and radial force (AF and RF) may influence the efficacy and complications of self-expandable metallic stent (SEMS) placement. We measured the MPs of various SEMSs and examined their influence on the SEMS clinical ability. Methods: We evaluated the MPs of 29 types of 10-mm SEMSs. RF was measured using a conventional measurement device. AF was measured using the conventional and new methods, and the correlation between the methods was evaluated. Results: A high correlation in AFs was observed, as measured by the new and conventional manual methods. AF and RF scatterplots divided the SEMSs into three subgroups according to structure: hook-and-cross-type (low AF and RF), cross-type (high AF and low RF), and laser-cut-type (intermediate AF and high RF). The hook-and-cross-type had the largest axial force zero border (>20°), followed by the laser-cut and cross types. Conclusions: MPs were related to stent structure. Hook-and-cross-type SEMSs had a low AF and high axial force zero border and were considered safest because they caused minimal stress on the biliary wall. However, the increase in RF must be overcome.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.11
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• pp.1584-1589
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• 2013

A new and significantly small guided and resonant structure is suggested to take over bulky metallic hollow waveguides used in military satellite transceivers. Below Ku-band, the conventional waveguides resulting in quite heavy transceivers will be replaced by the low profile SIW(substrate integrated waveguide) structures that are distinguished from the others in that the suggested ones have much lower cut-off frequencies by the circuital configuration of DNG(dobule negative) constitutive parameters and become even smaller than the other SIWs. The design scheme is validated by the circuit and full-wave simulations from the guided, resonant, and coupled structures. Besides, a bandpass filter as the suggested coupled structure is fabricated with a cheap substrate in a low-budget fabrication process and its frequency response is measured as verification of the purpose of the design.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.687-692
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• 2008

In a nuclear power plant, loose part monitoring and its diagnostic technique is one of the major issues for ensuring the structural integrity of the reactor system. Typically, accelerometers are mounted on the surface of a reactor vessel to localize impact location caused by the impact of metallic substances on the reactor system. However, in some cases, the number of the accelerometers is not enough to estimate the impact location precisely. In such a case, one of alternative plan is to utilize another type sensors that can measure the vibration of the reactor structure even though the measuring frequency ranges are different from each others. The AE sensors installed on the reactor structure can be utilized as additional sensors for loose part monitoring. In this paper, we proposed a new method to estimate impact location by using both accelerometer signal and AE signal, simultaneously. The feasibility of the proposed method is verified by an experiment. The experimental results demonstrate that we can enhance the reliability and precision of the loose part monitoring.

• Smart Structures and Systems
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• v.8 no.1
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• pp.93-105
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• 2011

This paper presents a flexible low-profile antenna sensor for fatigue crack detection and monitoring. The sensor was inspired by the sense of pain in bio-systems as a protection mechanism. Because the antenna sensor does not need wiring for power supply or data transmission, it is an ideal candidate as sensing elements for the implementation of engineering sensor skins with a dense sensor distribution. Based on the principle of microstrip patch antenna, the antenna sensor is essentially an electromagnetic cavity that radiates at certain resonant frequencies. By implementing a metallic structure as the ground plane of the antenna sensor, crack development in the metallic structure due to fatigue loading can be detected from the resonant frequency shift of the antenna sensor. A monostatic microwave radar system was developed to interrogate the antenna sensor remotely. Fabrication and characterization of the antenna sensor for crack monitoring as well as the implementation of the remote interrogation system are presented.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.4
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• pp.456-463
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• 2018

With the development of weapon systems by mounting various sensors, it makes important to analyze the precise functioning of sensor to external environment. In the case of small arms with magnetic sensor, the malfunction of small arms might be caused by strong external magnetic fields. In this study, the effects of magnetic sensor on external magnetic fields were analyzed, and optimal magnetic shield and shield structure were designed through M&S. In addition, the magnetic-shielding effectiveness of magnetic sensor in small arms was verified with commercial shielding materials. As a result, it was demonstrated that the Fe-Cu-Si-Nd-B with the structure of multi-layer metallic shields was shown the magnetic-shielding effectiveness of 83 % for an external permanent magnet and 19 % for an alternating magnetic field of 180 dBpT at 60 Hz, respectively.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.417-420
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• 2006

The composition and structure of dendrite phase within $Zr_{76.11}Ti_{4.20}Cu_{4.51}Ni_{3.16}Be_{1.49}Nb_{10.53}$ bulk metallic glass (BMG) were confirmed by using an EPMA, XRD and TEM, respectively. The chief elements of dendrite phase were Zr-Ti-Nb and had a BCC structure. The thermal properties of this BMG have been then subsequently investigated by using a differential scanning calorimeter (DSC). The glass transition and crystallization onset temperatures were determined as $339.7^{\circ}C$ and $375.8^{\circ}C$ for this alloy, respectively. Mechanical properties have also been examined by conducting a series of uniaxial compression tests at various temperatures within supercooled liquid region under the strain rates between $10^{-4}/s$ and $3{\times}10^{-2}/s$. The deformation behavior of BMG composite within supercooled liquid region is similar to one of Vit-1 exhibiting amorphous single phase alloy. The flow stresses of BMG composite, however, are entirely higher than those of Vit-1 because dendrite phases are interfere with moving of atoms.

• Journal of Surface Science and Engineering
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• v.40 no.1
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• pp.16-22
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• 2007

Recently, mesoporous metallic materials are becoming more and more important in various applications like catalysts, electrochemical detectors, batteries, and fuel cells because of their high surface area. Among the various methods for manufacturing mesoporous structure, surfactant templating method followed by electroplating has been tried in this study. A mesoporous metallic film was prepared by electrodeposition from electroplating solution mixed with surfactant template. Nonionic type lyotropic liquid crystalline surfactant, Brij56, and nickel acetate based solution were selected as a template material and electroplating solution, respectively. To determine the content of surfactant forming a hexagonal column structure, the phase diagram of electroplating solution and surfactant mixture has been exploited by polarized optical microscopy equipped with heating and cooling stage. Nickel films were electroplated on Cu foil by stepwise potential input method to alleviate the concentration polarization occurred during the electroplating process. TEM and XRD analyses were performed to characterize the size and shape of mesostructures in manufactured nickel films, and electrochemical characterization was also carried out using cyclic voltammetry.