• Journal of the Korea Concrete Institute
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• v.27 no.2
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• pp.103-113
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• 2015

This paper studies impact performance of wire-mesh and steel fiber-reinforced concrete based on high-velocity impact experiments using hard spherical balls. In this experimental study, panel specimens were tested with various parameters such as steel fiber volume fraction, presence/absence of wire mesh, panel thickness, impact velocity, and aggregate size for the comparison of impact resistance performance for each specimen. While improvement of the impact resistance for reducing the penetration depth is barely affected with steel fiber volume fraction, the impact resistance to scabbing and perforation is improved substantially. This was due to the fact that the steel fiber had bridging effects in concrete matrix. The wire mesh helped minimizing the crater diameter of front and back face and enhanced the impact resistance to scabbing and perforation; however, the wire mesh did not affect the penetration depth. The wire mesh also reduced the bending deformation of the specimen with wire mesh, though some specimens had splitting bond failure on the rear face. Additionally, use of 20 mm aggregates is superior to 8 mm aggregates in terms of penetration depth, but for reducing the crater diameter on front and back faces, the use of 8 mm aggregates would be more efficient.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.4
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• pp.367-375
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• 2014

In numbers of kinds of heat exchanger, the shell-tube heat exchanger is the most commonly used type of heat exchanger in the industry field. In order to improve the thermal performance of the heat exchanger, this study was analyzed heat transfer characteristics according to arrangement of baffle and direction of baffle and bump phase of baffle about shell-tube heat exchanger using appropriate SST (Shear Stress Transport) turbulence model for flow separation and boundary layer analysis. As the boundary condition for CFD (Computational Fluid Dynamics) analysis, the inlet temperature of shell side was constantly 344 K and the variation of the water flow rate was 6, 12, 18 and 24 l/min. As the result of analysis, zigzag baffle arrangement enhances heat transfer rate and pressure drop. Furthermore, in the direction of the baffle, heat transfer rate is more improved with vertical type and angle $45^{\circ}$ type than existing type, and pressure drop was little difference. Also, the bump shape of baffle surface contributes to heat transfer rate and pressure drop improvement due to the increased heat transfer area. Through analysis results, we knew that the increase of the heat transfer was influenced by flow separation, fluid residual time, contact area with the tube, flow rate, swirl and so on.

• Corrosion Science and Technology
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• v.8 no.2
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• pp.53-61
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• 2009

In this study, both evaluations by visual imaging for exterior view of coating and by EIS were executed for epoxy primer coated specimens deteriorated by accelerated test, and comparison and analysis were carried out for 2 evaluation methods. In the comparison between total damaged area ratio acquired by image processing method and deterioration point, higher deterioration points were appeared for rusted specimens than for non-rusted specimens. It is attributed that deterioration point per unit area ratio given for rust is higher than for peeling. In the comparison between total damaged area ratio and EIS result, impedance of coating was largely decreased as about TEX>$10^4{\Omega}{\cdot}cm^2$ or less when rust area ratio is more than about 0.1%, and blistering area ratio is more than about 3%. Charge transfer resistance ($R_{ct}$) and double layer capacitance ($C_{dl}$) values were appeared for all specimens except 2 ones, which shows that water is accumulated and steel substrate is corroded at coated film-steel interface. In the comparison between deterioration point and EIS result, more than 10 points as deterioration point were given for specimens of below $10^6{\Omega}{\cdot}cm^2$ of impedance at low frequency. For specimens deteriorated by NORSOK cyclic test, impedance was lowest of all, though deterioration point was not high. It is thought to be attributed that coating system and accelerated deterioration condition of cyclic tested specimens were different from those of main specimens. From the result, it is thought that coating resistance can be relatively more decreased than deterioration degree estimated from exterior view under more severe corrosion environment or in the present of more complex deterioration factors.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.6
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• pp.98-105
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• 2016

In this study, projectiles with 2 kinds of nose shape: spherical and flat were impacted into normal concrete and fiber reinforced concrete panels. The fracture depth and form, crater diameter, tensile strain at rear face were evaluated. It was confirmed that smaller projectile nose areas resulted in deeper penetrations associated with concentrated impact forces and small front-face crater diameters in impact test. Conversely, larger projectile nose areas resulted in shallower penetrations and larger front-face fracture diameters. Similar front-face failure and strain distribution relationships based on the projectile nose shape were observed for normal and fiber-reinforced concrete although the rear-face tensile strain and scabbing were significantly reduced by the fiber reinforcement. In addition, a direct relationship was confirmed between the penetration depth based on the projectile nose shape and the tensile strain on the rear face. Thus the impact strain behavior is required to predict the scabbing behavior with penetration depth.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.3
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• pp.53-64
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• 2018

In this study, computational simulation was performed to investigate the characteristics of air/fuel mixing according to the shape of the injector exit when the transverse jet was injected into a supersonic flow. Non-reacting flow simulation was conducted with fixed mass flow rate and the same cross-sectional area. To validate the results, free stream Mach number and jet-to-crossflow memetum ratio are set to 3.38 and 1.4, respectively, which is same as the experimental condition. Further, separation region, structure of the under-expended jet, jet penetration height, and flammable region of hydrogen for five different injectors compared.

• Journal of the Korean Wood Science and Technology
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• v.14 no.1
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• pp.3-44
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• 1986

In order to obtain the basic physical and mechanical properties of steel wire reinforced particleboard, particleboards were formed with large particles through 2.11 mm (12 meshes) and retained on 1.27mm (20 meshes) sieves and small particles through 1.27mm (20 meshes) and retained on 0.42mm (60 meshes) sieves from the plywood mill wastes of meranti (Shorea spp.) in the form of pallmanchips, applying urea-formaldehyde resin as an adhesive on the particle surface in 10 percent on the oven dried weight of particles, and arranging steel wires of 1mm in diameter 5,10,15,20, and 25mm in longitudinal and transverse direction with crossing in the mid of the board depth in single layer boards, 10mm in longitudinal or transverse direction without crossing in two layers and 10mm in longitudinal and transverse directions with and without crossing in three steel wire layers boards. The stepwise 9-minutes-multi-pressing schedule in 5 minutes at 35 kgf/$cm^2$, 2.5 minutes at 25 kgf/$cm^2$. and 1.5 minutes at 15 kgf/$cm^2$ was applied for $300{\times}200{\times}13$mm board at the temperature of 160$^{\circ}C$ in a hot press. Specific gravity, thickness swelling, bending properties of modulus of rupture (MOR), modulus of elasticity(MOE), work to proportional limit, and work to ultimate load, internal bond (IB), and screw holding power(SHP) of the reinforced boards were analyzed on the wire openings and wire layers. The results obtained are summarized as follows; 1) In specific gravity, particleboards with large particles and small particles had higher value with more steel wire placements and more steel layers composition, 2) Particleboards with large particles in accordance with more steel wire liners composition gave very poor thickness swelling. 3) The mechanical properties of particleboards formed with large or small particles were reinforced with more steel wire layers. Therefore, bending strength was improved in modulus of rupture, modulus of elasticity, and work to ultimate load. Especiallv, particleboards with two or three steel wire layers showed the tension lamination effect when the steels in lower steel wire layer were oriented parallel to the board length. 4) The modulus of rupture, modulus of elasticity, and work to ultimate load in bending varied with opening area, distance of lengthwise wires multipled by distance of transverse wires. Particleboards formed with large particles resulted in higher value in modulus of rupture with 1.5-3 $cm^2$ opening area, 1-2cm distance between transverse wires, and 1.5-2.5cm distance between lengthwise wires. Particle boards formed with small particles showed higher value with 0.5-1.5$cm^2$ or 3.75-6.25 $cm^2$ opening area, 0.5 or 2.5cm distance between transverse wires. 5) In modulus of elasticity, particleboards formed with large particles with one steel wire layer suggested higher value with 5-3$cm^2$ opening area, 1-2.5cm distance between transverse wires and also 1-2.5 cm distance between lengthwise wires. Particleboards formed with small particles showed higher value with 0.75-1.25$cm^2$ or 3-6.25$cm^2$ opening area and 0.5 or 2.5cm distance between transverse wires. 6) Particleboards formed with large particles gaved higher value in work to ultimate load with 1-3$cm^2$ opening area. Particleboards formed with small particles showed increasing tendancy with decreasing opening area. 7) In internal bond and screw holding power, particleboards formed with large particles had increasing value in two and three steel wire layers compositions, but particleboards formed with small particles showed no difference. Particleboards formed with large particles containing one steel wire layer showed no difference in internal bond and screw holding power, and particleboards formed with small panicles containing one steel wire layer resulted in increasing value in internal bond and decreasing value in screw holding power in accordance with increase in opening area.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.985-991
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• 2010

The objective of this work was to investigate the pintle-tip shape effect on nozzle flow and thrust by cold flow test. When nozzle throat area was decreased by pintle movement, chamber pressure was increased monotonously but thrust was increased differently according to every pintle-tip shape. At the same chamber pressure and nozzle throat area, thrust of convex pintle-tip shape was mostly larger than that of concave one. Nozzle wall pressure distribution and magnitude of pintle-tip load depended on the pintle-tip shape, pintle position and nozzle throat area.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.243-244
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• 2010

Reinforced concrete beam are very diverse materials that are used to bending reinforcement. Recently the case of FRP flexural reinforcement is actively being used is an excellent weight - rigidity. However, use of FRP bending reinforcement in brittleness material properties of concrete in an actual field application causes destruction of detachment and attachment is being considered as a major cause of destruction. For hybrid laminating plates, tensile and three-point bending tests were performed considering various designs and fabricating methods for hybrid FRP plates. Tensile property of each test specimen was investigated and the research parameter of hybrid laminating plates considered here is the combining ratio of fiber to aluminum contents.

• Applied Chemistry for Engineering
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• v.25 no.5
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• pp.520-525
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• 2014

In this paper, the effect of silane-treated silicas and epoxidized soybean oil (ESBO) addition on adhesion properties of silicas-filled epoxy adhesives was examined. The silicas were treated by ${\gamma}$-methacryloxy propyltrimethoxy silane (MPS), ${\gamma}$-glycidoxy propyl trimethoxy silane (GPS), and ${\gamma}$-mercapto propyl trimethoxy silane (MCPS). Surface and structural properties of the adhesives were determined by using scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FT-IR). The t-peel strength of the adhesives was estimated using the universal testing machine (UTM). And, the equilibrium spreading pressure, surface free energy, and specific surface area were investigated by BET methods with $N_2$/77 K adsorption. As a result, the peel strength of the adhesives was increased in the presence of silane-treated silicas in the adhesives compared to that of untreated silicas. This result indicated that the silane coupling agent played an important role in improving the dispersion of silicas in epoxy adhesives. And, the adhesives treated by MCPS were superior to the others in adhesion.

• Journal of the Korean Electrochemical Society
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• v.21 no.3
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• pp.47-54
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• 2018

To maximize the areal capacity($mAh\;cm^{-2}$) of $LiNi_{0.5}Co_{0.2}Mn_{0.3}O_2$(NCM523) electrode with the same loading level of $15mg\;cm^{-2}$, three NCM523 electrodes with 4, 2, and 1 wt% poly(vinylidene fluoride)(PVdF) binder content are fabricated. Due to the delamination issue of electrode composite at the edge during punching process, the 1 wt% electrode is excluded for further evaluation. When the PVdF binder content decreases from 4 to 2 wt%, both adhesion strength and shear stress decrease from 0.4846 to $0.2627kN\;m^{-1}$ by -46% and from 3.847 to 2.013 MPa by -48%, respectively. Regardless of these substantial decline of mechanical properties, their initial electrochemical properties such as initial coulombic efficiency and voltage profile are almost the same. However, owing to high loading level, the 2 wt% electrode not only exhibits worse cycle performance than the 4 wt% electrode, but also cannot maintain its mechanical integrity only after 80 cycles. Therefore, if the binder content is reduced to increase the area capacity, the mechanical properties as well as the cycle performance must be carefully evaluated.