• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.3
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• pp.471-476
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• 2021

Soft magnetic composite (SMC) materials based on powder metallurgy have a number of advantages over the conventional electrical steel sheets commonly used in electric machines. Thus, technologies related to these materials have shown significant improvement in recent years. In general, SMCs are magnetically isotropic owing to the shape of the powder, which makes them suitable for the construction of electric machines with three-dimensional flux and complex structures. However, the materials with isotropic magnetic properties (such as SMCs) have complex vector hysteresis; thus, it is very difficult to predict accurate loss properties. Therefore, we manufactured ring-type specimens of electrical steel sheets and SMC, which analyzed their magnetic properties according to the specimen size, and performed the electromagnetic field analysis of a high-speed permanent magnet (PM) motor driven at 800 Hz or higher using the measured magnetic information to compare the core loss of the motor. The reliability of this paper has been verified by measuring the efficiency after manufacturing the motor.

• Tunnel and Underground Space
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• v.34 no.1
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• pp.71-87
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• 2024

In deep geological disposal of high-level radioactive waste, the surrounding rock at the immediate vicinity of the deposition hole may experience localized changes in permeability due to in-situ stress at depth, swelling pressure from resaturated bentonite buffer, and the heat generated from the decay of radioactive isotopes. In this study, experimental data on changes in permeability of granite, a promising candidate rock type in South Korea, were obtained by applying various confining pressures and temperature conditions expected in the actual disposal environment. By conducting the permeability test on KURT granite specimens under three or more hydrostatic pressure conditions, the relation in which the permeability decreases exponentially as the confining pressure increases was derived. The temperature-induced changes in permeability were found to be negligible at temperatures below the expected maximum of 90℃. In addition, by establishing a relation in which the initial permeability is proportional to the power of the initial porosity, it was possible to estimate permeability value for granite with a specific porosity under a certain confining pressure.

• Journal of the Korea Concrete Institute
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• v.21 no.2
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• pp.159-168
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• 2009

In this study, strength, stiffness and confinement effect with stress-strain and stress-volumetric strain curves for improved uniaxial compressive behavior of RC circular columns laterally confined with prestressing aramid fiber strap were experimentally investigated. The test variables were the specimens with or without axial reinforcing bar and the number and spacing of strap, prestressing level, the types of reinforcing fiber (CFS, GFS). As a result, the failure type of the columns was very stable and strength increase rate was about 73% comparison with the general RC columns. Moreover, the strain increase rate is very small and the axial displacement confinement effect was very effective compared with existry methods (CFS, GFS), the initial and final lateral confinement effect was excellent.

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.745-752
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• 2012

This paper studies the effect of the compressive strength for combined alkali-activated slag mortars. The effect of activators such as alkali type and dosage factor on the strength was investigated. The alkalis combinations made using five caustic alkalis (sodium hydroxide (NaOH, A series), calcium hydroxide ($Ca(OH)_2$, B series), magnesium hydroxide ($Mg(OH)_2$, C series), aluminum hydroxide ($Al(OH)_3$, D series), and potassium hydroxide (KOH, E series)) with sodium carbonate ($Na_2CO_3$) were evaluated. The mixtures were combined in different dosage at 1M, 2M, and 3M. The study results showed that the compressive strength of combined alkali-activated slag mortars tended to increase with increasing sodium carbonate. The strength of combined alkali-activated slag mortars was better than that of control cases (without sodium carbonate). The result from scanning electron microscopy (SEM) analysis confirmed that there were reaction products of calcium silicate hydrate (C-S-H) and alumina-silicate gels from combined alkali-activated slag specimens.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.2
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• pp.79-86
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• 2018

In this study, emulsion type hydrophobic admixture was prepared by mixing polyvinyl alcohol surfactant, polymethyl hydro-siloxane and meta kaolin, and the compressive strength and mechanical properties such as permeability and contact angle test of the mortar were evaluated. The developed hydrophobic admixture showed no decrease in strength and the mortar specimen with magnesium oxide developed the early strength. In the case of permeability, total seepage was significantly decreased when the hydrophobic admixture was directly mixed with the mortar, but the effect of meta kaolin contained in hydrophobic admixture was not significant. The surface of specimens coated with hydrophobic admixture shows that the contact angle on the surface was highly increased compared with reference mortar specimen. Further researches to obtain the optimum mix proportion of the PVA fiber, nano-silica and meta kaolin for producing the super-hydrophobic surface are required.

• The Journal of Korean Academy of Prosthodontics
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• v.22 no.1
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• pp.123-132
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• 1984

To evaluate the microstructure of various combination clasp joint in removable partial denture, the auther selected framework alloys (Type IV gold alloy, Dentaurium, Ticonium 100) and wrought wires (gold alloy, Ticonium) for this study. Twelve series of combination joints were made by investment soldering technic and wrought wire embedded casting technic. All specimens were cut cross-sectionally and longitudinally, then examined with metallurgical microscope. The results were as follows; Some diffusion was observed in the properly constructed combination clasp joints. In soldered joints, empolying precious alloys were more favorable than non-precious alloys. In castion joints, assemblage of same alloy between framework and wrought wire was superior to other groups. Some impurities were observed in both joints by technical problems.

• Journal of Korean Society of Steel Construction
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• v.24 no.4
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• pp.411-422
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• 2012

The purpose of this study is to evaluate the flexural and shear capacity of steel wire-integrated void deck plate slabs. In order to evaluate flexural and shear capacity, we make five 150mmspecimens and three 200mmspecimens by slab depth as main variable. Each series of specimen is comprised of an existing steel wire-integrated deck-plate slab and two specimens using topping depth as variable. From the series of experiments, steel wire-integrated void deck plate slabs has any decline in flexural and shear performance. Therefore, a void-deck-plate slab which inserts Omega-steel plate showed reducing a using concrete-volume and had flexural and shear capacity following existing steel wire-integrated deck-plate.

• Journal of Korean Society of Steel Construction
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• v.28 no.3
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• pp.185-194
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• 2016

This paper presents the finite element method results for HSS(Hollow Square Section) steel columns strengthened with Carbon Fiber Reinforced Polymer Plastic(CFRP) sheets. 6 specimens were fabricated and the specimen groups were non-compact short columns, slender short columns, and non-compact long columns. Test parameter was the number of CFRP ply. The finite element analysis was performed by using ANSYS Workbench V.14.0 and the results of FEM were compared with those of Test for failure mode, load-displacement curve, maximum load, and initial stiffness. The comparisons between experimental observations and computed results show that the analyses provided good correlation to actual behavior. Finally, the buckling stress were calculated according to the AISC cold-formed structure provision and the retrofitting effect were verified for each section type.

• Journal of Radiation Protection and Research
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• v.41 no.2
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• pp.93-99
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• 2016

Background: Industrial X-ray CT system is normally applied to non-destructive testing (NDT) for industrial product made from metal. Furthermore there are some special CT systems, which have an ability to inspect nuclear fuel assemblies or rocket motors, using high power and high energy (more than 6 MeV) pulsed X-ray source. In these case, pulsed X-ray are produced by the electron linear accelerator, and a huge number of photons with a wide energy spectrum are produced within a very short period. Consequently, it is difficult to measure the X-ray energy spectrum for such accelerator-based X-ray sources using simple spectrometry. Due to this difficulty, unexpected images and artifacts which lead to incorrect density information and dimensions of specimens cannot be avoided in CT images. For getting highly precise CT images, it is important to know the precise energy spectrum of emitted X-rays. Materials and Methods: In order to realize it we investigated a new approach utilizing the Bayesian estimation method combined with an attenuation curve measurement using step shaped attenuation material. This method was validated by precise measurement of energy spectrum from a 1 MeV electron accelerator. In this study, to extend the applicable X-ray energy range we tried to measure energy spectra of X-ray sources from 6 and 9 MeV linear accelerators by using the recently developed method. Results and Discussion: In this study, an attenuation curves are measured by using a step-shaped attenuation materials of aluminum and steel individually, and the each X-ray spectrum is reconstructed from the measured attenuation curve by the spectrum type Bayesian estimation method. Conclusion: The obtained result shows good agreement with simulated spectra, and the presently developed technique is adaptable for high energy X-ray source more than 6 MeV.

• Tribology and Lubricants
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• v.33 no.1
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• pp.15-22
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• 2017

Because the running speed of vehicles is increasing and a shorter braking distance is required, high heat-resistant brake pads are needed to satisfy the requirements of customers and car makers. In the near future, hazardous materials such as Cu, Cr, Zn, and Sb will be restricted from use in friction materials. Ceramic composites reinforced by carbon fibers are good candidates for eco-friendly friction materials. In this study, we develop ceramic composite friction materials. The friction materials are composed of carbon fibers, Si, SiC, graphite, and phenol resin and are prepared by hot forming and heat treatment at high temperatures. The density, void ratio, and compressive strength are $1.59-1.66g/cm^3$, 16.6-20, and 70-90 MPa, respectively. Friction and wear tests are performed using a pin-on-plate-type reciprocating friction tester at 25, 100, and $200^{\circ}C$. The counterpart material is a CrMoV steel extracted from a KTX brake disc. Friction coefficient, wear amount, and wear mechanism are measured and examined. We determine that the friction coefficients depend on the temperature and the fluctuation of the friction coefficients is larger at higher temperatures. The amount of wear increases with the surface temperatures of the specimens. The tribological properties of the developed composites are similar to those of a Cu-based sintered friction material. Through this study, it is confirmed that ceramic composite materials can be used as friction materials.