• Aerospace Engineering and Technology
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• v.9 no.1
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• pp.72-77
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• 2010

A hydraulic test on a filament wound case of Kick-Motor was conducted to evaluate the structural stiffness degradation and to confirm the burst performance. Failure criteria have been defined with bursting above 150% of MEOP(Maximum Expected Operation Pressure) and failure in the cylinder. The analysis result showed that filament fiber in the cylinder should be broken at about 2088psig. From a hydraulic test it has been verified that composite case meets the failure requirements, and that the stiffness does not decrease even after a year since the manufacturing.

• Steel and Composite Structures
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• v.39 no.2
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• pp.135-148
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• 2021

Hollow structural section (HSS) columns have been increasingly popular due to their structural and architectural merits. However, practical difficulty lies in developing proper connections. The through-diaphragm connections are considered as suitable connection type that is widely adopted in Asian countries. However, the stress concentration occurs at the location connecting through-diaphragm and steel beam. Furthermore, the actual load path from the beam flange is not uniformly transferred to the HSS column as conventionally assumed. In this paper, tensile tests were further conducted on three additional specimens with beam flange plate to evaluate the load versus displacement response. The load-displacement curves, yield and ultimate capacity, ductility ratio were obtained. Furthermore, the strain development at different loading levels was discussed comprehensively. It is shown that the studied connection configuration significantly reduces the stress concentration. Meanwhile, simplified trilinear load-displacement analytical model for specimen under tensile load was presented. Good agreement was found between the theoretical and experimental results.

• Journal of Korea Multimedia Society
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• v.25 no.3
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• pp.528-536
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• 2022

The purpose of this study is to help preschool children in the interface design of educational game APP at the psychological level. The conceptual model is constructed through the Technology Acceptance Model (TAM) to explore the perceived usefulness and perceived ease of use when children are playing educational game APP. The empirical study was conducted in the form of questionnaires collected after children used game. The research subjects were 3-6 years old children, and the research tool was the game app. Data collection under the guidance of their parents. The research shows that children educational game experience elements can effectively increase preschool children's psychological perception of educational games. Perceived ease of use also increases trust in educational games for children. The results were as follows: 1. Cronbach's Alpha and KMO were 0.969 and 0.955, and the P value was significant, which passed the reliability and validity test. 2. Through confirmatory factor analysis (Model fit index, Composite reliability, discriminant validity), we found that user experience is closely related to perceived usefulness and perceived ease of use. 3. The path analysis of the relationship proves that perceived ease of use play a key role in trusting preschool children educational game APP.

• Journal of Electrochemical Science and Technology
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• v.12 no.2
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• pp.285-295
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• 2021

The inverse spinel Cobalt ferrite (CoFe₂O₄, CFO) is considered to be a promising alternative to commercial graphite anodes for lithium ion batteries (LIBs). However, the further development of CFO is limited by its unstable structure during battery cycling and low electrical conductivity. In an effort to address the challenge, we construct three-dimensional hierarchical flower-like CFO nanoclusters (CFO NCs)-decorated carbonized cotton carbon fiber (CFO NCs/CCF) composite. This structure is consisted of microfibers and nanoflower cluster composited of CFO nanoparticle, in which CCF can be used as a long-range conductive matrix, while flower-like CFO NCs can provide abundant active sites, large electrode/electrolyte interface, short lithium ion diffusion path, and alleviated structural stress. As anode materials in LIBs, the flower-like CFO NCs/CCF exhibits excellent electrochemical performance. After 100 cycles at a current density of 0.3 A g^-1, the CFO NCs/CCF delivers a discharge/charge capacity of 1008/990 mAh g^-1. Even at a high current density of 15 A g^-1, it still maintains a charge/discharge capacity of 362/361 mAh g^-1.

• Steel and Composite Structures
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• v.45 no.6
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• pp.865-876
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• 2022

The slit members have lower strength and lower stiffness, which might lead to lower energy dissipation. In order to improve the seismic performance of the slit members, the paper proposes the shear lead damper, which has stable performance and small deformation energy dissipation capacity. Therefore, the shear lead damper can set in the vertical silts of the slit member to transmit the shear force and improve energy dissipation, which is suitable for the slit member. Initially, the symmetrical teeth-shaped lead damper was tested and analyzed. Then the staggered teeth-shaped lead dampers were developed and analyzed, based on the defect analysis and build improvements of the symmetrical specimen. Based on the parameter analysis, the main influence factors of hysteretic performance are the internal teeth, the steel baffles, and the width and length of damper. Finally, the theoretical analysis was presented on the hysteretic curve. And the skeleton curve and hysteresis path were identified. Based on the above theoretical analysis, the design method was proposed, including the damping force, the hysteresis model and the design recommendations.

• Progress in Superconductivity and Cryogenics
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• v.10 no.1
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• pp.24-27
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• 2008

For the development of superconducting fault current limiters(SFCLs) having large current capacity, we fabricated an SFCL element that consists of Bi-2212 superconductor and Cu-Ni alloy tubes. First, Ag was plated on the surface of the Bi-2212 for the enhancement of soldering process. On the Ag-plated Bi-2212 tube, a Cu-Ni alloy tube was soldered using optimized solders and soldering conditions. The BSCCO/Cu-Ni composite was processed mechanically to have a helical shape for the improvement of the SFCL characteristics. The total current path of the SFCL element was 1330 mm long with 12 turns, and had critical current of 340 A at 77 K. Finally, we carried out the fault test using the fabricated SFCL element. It showed successful current limiting performance under the fault condition of 50 $V_{rms}$ and 5.5 kA. From the results, the rated voltage of the SFCL element was decided to be 0.4 V/cm, and the power capacity was 12 kVA at 77 K. The fabrication process of the SFCL and the fault test results will be presented.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.1
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• pp.55-61
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• 2015

Stretchable electrode materials are focused to apply to flexible device such as e-skin and wearable computer. Used as a flexible electrode, increase in electrical resistance should be minimalized under physical strain as bend, stretch and twist. Carbon black is one of candidates, for it has many advantages of low cost, simple processing, and especially reduction in resistivity with stretching. However electrical conductivity of carbon black is relatively low to be used for electrodes. Instead graphene is one of the promising electronic materials which have great electrical conductivity and flexibility. So it is expected that graphene added carbon black may be proper to be used for stretchable electrode. In this study, under stretching electrical property of graphene added carbon black composite electrode was investigated. Mechanical stretching induced cracks in electrode which means breakage of conductive path. However stretching induced aligned graphene enhanced connectivity of carbon fillers and maintained conductive network. Above all, electronic structure of carbon electrode was changed to conduct electrons effectively under stretching by adding graphene. In conclusion, an addition of graphene gives potential of carbon black composite as a stretchable electrode.

• Journal of the Korea Institute of Building Construction
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• v.9 no.6
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• pp.161-168
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• 2009

In an architectural construction, underground construction is a critical path forming a major part of the total construction period and cost, and particularly in big cities, its size has been increasing every year. A basement wall currently constructed in the field needs a large functional work force, and the construction is under progress by the Euroform and Soldier system, which is disadvantageous in terms of the construction period. Therefore, in this research, non-supporting forms which are applicable to the buildings construction were developed, based on the non-supporting forms partly used in some civil engineering works. In addition, the size of a form was assumed and its economical efficiency was compared to that of the Euroform and Soldier system which is used most in construction fields, and the results were analyzed. The study results showed that the construction cost of composite non-supporting forms was higher than that of the Euroform and Soldier system by about 8%, and the construction cost of non-composite non-supporting forms were lower than that of the Euroform and Soldier system by about 9%. However, in the case of composite non-supporting forms, the amount of concrete and reinforcing rods remarkably decreased in structural construction, so it has the effect of an economical cost reduction compared to the construction cost of existing walls by about 35%

• Journal of the Microelectronics and Packaging Society
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• v.30 no.4
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• pp.61-68
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• 2023

In this study, Sn-3.5Ag-15.0Fe composite solder was manufactured and applied to TLP bonding to change the entire joint into a Sn-Fe IMC(intermetallic compound), thereby applying it as a high-temperature solder. The FeSn₂ IMC formed during the bonding process has a high melting point of 513℃, so it can be stably applied to power modules for power semiconductors where the temperature rises up to 280℃ during use. As a result of applying ENIG surface treatment to both the chip and substrate, a multi-layer IMC structure of Ni₃Sn₄/FeSn₂/Ni₃Sn₄ was formed at the joint. During the shear test, the fracture path showed that cracks developed at the Ni₃Sn₄/FeSn₂ interface and then propagated into FeSn₂. After 2hours of the TLP joining process, a shear strength of over 30 MPa was obtained, and in particular, there was no decrease in strength at all even in a shear test at 200℃. The results of this study can be expected to lead to materials and processes that can be applied to power modules for electric vehicles, which are being actively researched recently.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.1
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• pp.85-91
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• 2013

This paper studied surface discharge characteristics by a dielectric constant and diameter of solid dielectrics in $N_2/O_2$ mixture gas. Applied electric field strength at $N_2/O_2$ mixture gas was changed from the dielectric constant and diameter of the solid dielectrics, and insulation performance of the $N_2/O_2$ mixture gas determined surface discharge voltage. In each of the diameter at the solid dielectrics, the surface discharge voltage was increased by lengthening surface distance, whereas increasing rate of the surface discharge voltage was different from gas pressure. Thus, In this paper, main factors of surface discharge are as follows. 1) Insulation performance of $N_2/O_2$ mixture gas, 2) Dielectric constant of solid dielectrics, 3) Surface discharge path. It was clear that the surface discharge voltage depend on the main factors. These results will be applied to useful data for an eco-friendly composite insulation design.