• Journal of the Korea Concrete Institute
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• v.29 no.3
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• pp.249-257
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• 2017

The purpose of this study was to contribute to the field application cost effectively and reasonably by developing the functional piles that make up for the defects of PHC piles. CFP (Concrete Filled Pretensioned Spun High Strength Concrete Pile with Ring type Composite shear connectors) piles developed in this study increases the compressive stress through enlarged cross section by rearranging composite shear connectors and filling the hollow part of PHC pile with concrete. And it improved shear and bending performance placing the rebar (H13-8ea) within the PHC pile and the hollow part of PHC pile of rebar (H19-8ea). In addition, the composite shear connectors were placed for the composite behavior between PHC pile and filled concrete. Placing Rebars (H13-8ea) of PHC pile into composite shear connector holes are sleeve-type mechanical coupling method that filling the concrete to the gap of the two members. Nonlinear finite element analyzes were performed to verify the performance of shear and bending moments and it deduced the spacing of the composite shear connectors. Through a various interpretation of CFP piles, it's proved that the CFP pile can increase the shear and bending stiffness of the PHC pile effectively. Therefore, this can be utilized usefully on the construction sites.

• Journal of the Korean GEO-environmental Society
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• v.19 no.3
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• pp.5-13
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• 2018

Recently, construction disasters in thawing season are increasing due to the ground collapse and it is related to the improper compaction during winter season. Compaction at sub-zero temperature reduces the compaction effect and the research of mechanical properties of thawed soil after winter compaction can be used as useful data to understand the behavior of the ground in the thawing season. On the other hand, the research interest in the unsaturated soil mechanics has been increasing in the field of the geotechnical engineering. Therefore, it is expected that the research of unsaturated characteristics under the compaction of sub-zero temperature and freezing & thawing condition provides information to the researchers in the related fields. Therefore, in this research, unsaturated soil-water characteristics test and unsaturated uniaxial compression test were conducted on the specimens compacted at sub-zero temperature and continuous freezing & thawing condition to investigate change of unsaturated characteristics and matric suction. Based on the test results, the change of matric suction and the decrease of strength and stiffness were observed with the freezing & thawing conditions. Especially in case of the weathered soil, the strength and matric suction were significantly reduced with lower temperature and more repetition of freezing & thawing cycles. This result implies that compaction of sub-zero temperature and freezing & thawing cycles will have a considerable influence on the stability of the ground.

• Korean Chemical Engineering Research
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• v.44 no.5
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• pp.513-519
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• 2006

We developed two kinds of the microchip for application to electrophoresis based on both glass and quartz employing the MEMS fabrications. The poly-Si layer deposited onto the bonding interface apart from channel regions can play a role as the optical slit cutting off the stray light in order to concentrate the UV ray, from which it is possible to improve the signal-to-noise (S/N) ratio of the detection on a chip. In the glass chip, the deposited poly-Si layer had an important function of the etch mask and provided the bonding surface properly enabling the anodic bonding. The glass wafer including more impurities than quartz one results in the higher surface roughness of the channel wall, which affects subsequently on the microflow behavior of the sample solutions. In order to solve this problem, we prepared here the mixed etchant consisting HF and $NH_4F$ solutions, by which the surface roughness was reduced. Both the shape and the dimension of each channel were observed, and the electroosmotic flow velocities were measured as 0.5 mm/s for quartz and 0.36 mm/s for glass channel by implementing the microchip electrophoresis. Applying the optical slit with poly-Si layer provides that the S/N ratio of the peak is increased as ca. 2 times for quartz chip and ca. 3 times for glass chip. The maximum UV absorbance is also enhanced with ca. 1.6 and 1.7 times, respectively.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.39 no.4
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• pp.341-349
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• 2002

Electrical, mechanical and sinterability properties of yttria-stabilized zirconia doped with 5.35wt% $Y_2$O$_3$(Y$_2$O$_3$- containing stabilized zirconia : YSZ) were studied as a function of $Al_2$O$_3$, CoO, Fe$_2$O$_3$ and MnO$_2$ addition. The ratio of monoclinic phase to tetragonal phase was changed by the addition of $Al_2$O$_3$, CoO, Fe$_2$O$_3$ and MnO$_2$ to 8.00 wt% and sintered density decreased with increasing $Al_2$O$_3$, CoO, Fe$_2$O$_3$ and MnO$_2$ addition. Fracture toughness increased with the increase of monoclinic to tetragonal phase ratio and was maximum at about 18%. When transition metals such as CoO, Fe$_2$O$_3$ or MnO$_2$ was added more than 1.5 wt%, the electrical conductivity of YSZ increased. But $Al_2$O$_3$ hardly affected the electrical conductivity of YSZ. The addition of $Al_2$O$_3$, CoO, Fe$_2$O$_3$ and MnO$_2$ into YSZ resulted in the more complex behavior of fracture toughness and hardness variation and the specimen with 1.5wt%-Fe$_2$O$_3$, 3.0wt%-Al$_2$O$_3$ and 1.5wt%-CoO showed the monoclinic to tetragonal phase ratio of 18% and the highest toughness of 10.8 MPa.m$^{1}$2/ and Vickers hardness of 1201 kgf/mm$^2$.

• Composites Research
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• v.29 no.2
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• pp.73-78
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• 2016

In this paper, The concept of a wheel with carbon fiber composite is to replace the conventional material used for a wheel hub, such as plastic, with a disk-type hub made of carbon fabric and epoxy resin. The impact load from the ground under real conditions was considered; a low-velocity impact test was conducted to evaluate the impact performance of the carbon wheel and compare it with that of a conventional plastic wheel. This study applied a 70 J impact load as a test condition. The impact energy was controlled in the test by adjustment of height and weight of impactor. The use of a carbon disk wheel hub was confirmed to reduce weight and generate an excellent repulsive force at low energy under conditions similar to real driving conditions. The results showed that the maximum load increased proportionally depending on the impact load, but the growth of the maximum load was reduced at a 20 J impact load and tended to decrease at a 45 J impact load. The carbon wheel showed excellent properties ; the level of rebounding was 35.3% and 19.1% of the total impact energy at impact loads of 5 J and 10 J, respectively. On the other hand, the carbon disk wheel rebounded less than 5% of the total energy due to crack generation of the thin carbon hub for impact loads of more than 20 J.

• Journal of Korea Foundry Society
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• v.40 no.2
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• pp.7-15
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• 2020

The high-temperature stability of Mg-8.0Zn-1.6Y (wt.%) alloys upon the addition of Ca has been investigated by characterizing the ignition temperature, microstructure, tensile and creep properties. The ignition temperature increases with an increase in the Ca content, indicating that an addition of Ca enhances the ignition resistance of the Mg-Zn-Y alloy. The as-cast microstructures of all tested alloys mainly consisted of the dendritic α-Mg matrix and I-phase (Mg₃Zn₆Y) at the grain boundaries. In the Ca-added Mg-8.0Zn-1.6Y alloys, the Ca₂Mg₆Zn₃ phase forms, with this phase fraction increasing with an increase in the Ca contents. However, a high volume fraction of the Ca₂Mg₆Zn₃ phase rather deteriorates the mechanical properties. Therefore, a moderate amount of Ca element in Mg-8.0Zn-1.6Y alloys is effective for improving the tensile and creep properties of the Mg-Zn-Y alloy. The Mg-8.0Zn-1.6Y-0.3Ca alloy exhibits the highest tensile strength and the lowest creep strain among the alloys investigated in the present study. The creep resistance of Mg-Zn-Y-Ca alloys depends on the selection of the secondary solidification phase; i.e., when Ca₂Mg₆Zn₃ forms in an alloy containing a high level of Ca, the creep resistance deteriorates because Ca₂Mg₆Zn₃ is less stable than the I-phase at a high temperature.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.4
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• pp.451-468
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• 2020

Aging tunnels with small cross-sections can cause chronic traffic jams. This problem can be solved by widening the tunnel. In general, when the tunnel is expanded, the outer portion of the existing tunnel is excavated through a mechanical or blasting method. Such excavation affects not only the surrounding ground but also the existing tunnel. The application of the pre-cutting method can be a solution to these problems effectively. Therefore, if the widening of tunnel is performed by applying pre-cutting method, analysis of the impact of this method must be performed. In this study, in order to analyze the effect of applying pre-cutting in tunnel widening, numerical analysis is performed at six ground grades, from grade I to weathered rock. The analysis is performed with the expanding lane and the excavation length of pre-cutting as variables. In addition, the analysis is focused on the displacement of crown of the existing tunnel and the enlarged tunnel. As a result, the crown displacement of the enlarged tunnel is confirmed to converge at the same value regardless of the excavation length of the pre-cutting when the tunnel widening is completed. In the case of existing tunnels, uplift of crown occurs within 5 m of the front of the tunnel surface, and the shorter the excavation length of pre-cutting is found to be effective in preventing the occurrence of uplift.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.2
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• pp.43-51
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• 2014

In 3-dimensional (3D) integrated package, thermal management is one of the critical issues due to the high heat flux generated by stacked multi-functional chips in miniature packages. In this study, we used numerical simulation method to analyze the thermal behaviors, and investigated the thermal issues of 3D package using TSV (through-silicon-via) technology for mobile application. The 3D integrated package consists of up to 8 TSV memory chips and one logic chip with a interposer which has regularly embedded TSVs. Thermal performances and characteristics of glass and silicon interposers were compared. Thermal characteristics of logic and memory chips are also investigated. The effects of numbers of the stacked chip, size of the interposer and TSV via on the thermal behavior of 3D package were investigated. Numerical analysis of the junction temperature, thermal resistance, and heat flux for 3D TSV package was performed under normal operating and high performance operation conditions, respectively. Based on the simulation results, we proposed an effective integration scheme of the memory and logic chips to minimize the temperature rise of the package. The results will be useful of design optimization and provide a thermal design guideline for reliable and high performance 3D TSV package.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.1
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• pp.83-90
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• 2017

In this paper, we evaluated the solderability of thin electroless nickel-electroless palladium-immersion gold (ENEPIG) plating layer for fine-pitch package applications. Firstly, the wetting behavior, interfacial reactions, and mechanical reliability of a Sn-3.0Ag-0.5Cu (SAC305) solder alloy on a thin ENEPIG coated substrate were evaluated. In the wetting test, maximum wetting force increased with increasing immersion time, and the wetting force remained a constant value after 5 s immersion time. In the initial soldering reaction, $(Cu,Ni)_6Sn_5$ intermetallic compound (IMC) and P-rich Ni layer formed at the SAC305/ENEPIG interface. After a prolonged reaction, the P-rich Ni layer was destroyed, and $(Cu,Ni)_3Sn$ IMC formed underneath the destroyed P-rich Ni layer. In the high-speed shear test, the percentage of brittle fracture increased with increasing shear speed.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.2
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• pp.217-226
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• 2018

Since the sides of a vehicle are designed asymmetrically unlike its front or rear, the degree of deformation of the car body greatly differs depending on the site of collision if a broadside collision takes place. When elastic deformation and plastic deformation occur in the car body occur due to a collision, the kinetic energy is absorbed into the body, and the momentum decreases. Generally, an analysis of traffic accidents analyzes the vehicle's behavior after a collision by the law of momentum conservation and corrects the error of the amount of energy absorption due to the deformation of the car body, applying a restitution coefficient. This study interpreted a finite element vehicle model applying the structure of the car body and the material properties of each part with LS-DYNA, analyzed the result and drew the restitution coefficient and the depth of penetration according to the contact area of the vehicle in a broadside collision between an SUV and a passenger car. When the finally calculated restitution coefficient and depth of penetration were applied to the examples of the actual traffic accidents, there was an effect on the improvement of the error in the result. It was found that when the initial input value, drawn using the finite element analysis model, it had a higher reliability of the interpretation than that of the existing analysis techniques.