• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.3
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• pp.1585-1593
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• 2015

3D-structured (embossed) aluminum sheets have been used in the heat insulation purpose for automative exhaust parts because of increasing their surface areas and stiffness reinforcement imposed in making the embossing pattern. However, there are many restrictions in press forming of the embossed sheet compared with the flat sheet (non-embossed one) because of its difference in the mechanical properties and the geometrical 3-dimensional shape. In this paper we investigated the deformation characteristic of embossed aluminum sheet in the incremental sheet forming process which has frequently used in the design verification and the trial manufacturing of sheet products. The single point incremental forming (SPIF) experiments for the rectangular cone forming using the CNC machine with a chemical wood-machined die and a circular tool shape showed that the formability of the embossed sheet are better than that of the flat sheet in view of the maximum angle of cone forming. This comes from the fact that the embossed sheet between the tool and the elastic die wall is plastically compressed and the flatted area contributes to increase the plastic deformation. Also the tool path along the outward movement from the center showed a better formability than that of the inward movement from the edge. However the surface quality for the tool path along the outward movement evaluated from the surface deflection is inferior than that of the tool path along the inward movement.

• Korean Chemical Engineering Research
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• v.48 no.1
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• pp.75-79
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• 2010

The precursor powders with thin wall structure were prepared by spray pyrolysis from the spray solution with ethylenediaminetetraacetic acid, citric acid and $NH_4Cl$ flux. The $BaMgAl_{10}O_{17}:Eu$ phosphor powders formed from the spray solution without organic additives and flux material had sizes of $1{\sim}5{\mu}m$ and hollow structure with high thickness at post-treatment temperature of $1,200^{\circ}C$. However, $BaMgAl_{10}O_{17}:Eu$ phosphor powders formed from the spray solution with ethylenediaminetetraacetic acid, citric acid and $NH_4Cl$ flux had fine size and plate-like shape. The mean crystallite sizes of the phosphor powders with fine sizes were 23, 35, and 33 nm when the content of $NH_4Cl$ flux were 0, 6, 35 wt% of phosphor. The photoluminescence intensity of the phosphor powders formed from the spray solution with the optimum amount of $NH_4Cl$ flux as 35 wt% was 215% of that of the phosphor powders formed from the spray solution without flux material.

• Resources Recycling
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• v.11 no.1
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• pp.3-8
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• 2002

In order to make the high purity Mn$_3$O$_4$powder for the raw material of soft ferrite, Mn is extracted from the dust and the extracted solution is refined. The dust is generated in producing a medium-low carbon ferromanganese and contains 90% Mn$_3$O$_4$. Mn$_3$O$_4$in the dust was reduced into MnO by roasting with charcoal. Injection of the 180g/L of the reduced dust into 4N HCI solution increased pH of the leaching solution higher than 5 and then a ferric hydroxide was precipitated. Because the ferric hydroxide co-precipitates with Si ion etc, Fe and Si ion was removed from the solution and the about 10% Mn solution was obtained. The solution was diluted with water to Mn-15000 ppm and $NH_4$F was injected into the diluted solution at $70^{\circ}C$ to the F-3000 ppm. As a result, Ca ion is precipitated as $CaF_2$and the residual concentration of Ca was 14 ppm. Injection of the equivalent (NH$1.5M_4$)$_2$$CO_3$solution as 2 L/min at $25^{\circ}C$ into the above solution precipitated a fine and high purity $MnCO_3$powder. The deposition was filtrated and roasted at $1000^{\circ}C$ for 2 hours. As a result, $MnCO_3$powder is converted into $Mn_3$$O_4$powder and it had $8.2\mu$m of median size. The final production is above 99% $Mn_3$$O_4$powder and it satisfied the requirement of high purity $Mn_3$$O_4$powder for a raw material of soft ferrite.

• Journal of Korean Society of Steel Construction
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• v.29 no.1
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• pp.25-36
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• 2017

In the 1994 Northridge earthquake, connection damage initiated from the beam bottom flange was prevalent. The presence of a concrete slab and resulting composite action was speculated as one of the critical causes of the prevalent bottom flange fracture. In this study, four seismic retrofit schemes are proposed in order to salvage welded steel moment connections with composite floor slabs in existing steel moment frames. Because top flange modification of existing beams is not feasible due to the presence of a concrete floor slab, three schemes of bottom flange modification by using welded triangular or straight haunches or RBS(reduced beam section), and beam web strengthening by attaching heavy shear tab were cyclically tested and analyzed. Test results of this study show that haunch and web-strengthened specimens can eliminate the detrimental effect caused by composite action and ensure excellent connection plastic rotation exceeding 5% rad. Design recommendations for each retrofit scheme together with supplemental numerical studies are also presented.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.61-69
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• 2004

The bridge piers under service suffered a brittle failure due to the deterioration of lap-spliced longitudinal reinforcement without developing its flexural capacity or ductility. The earthquake induced lateral force results in tension which causes bond-slip failure at the lap-spliced region in circular bridge piers. In this case, such a brittle failure can be controlled by the seismic retrofit using FRP laminated circular tube. The retrofitted piers using FRP laminated circular tube showed significant improvement in seismic performance due to FRP's confinement effect. This paper presents the analytical results on the seismic strengthening effect of circular bridge piers with poor lap-splice details and strengthened with FRP laminated circular tube. FRP's confinement effect is predicted by the classical elasticity solution for the laminated circular tube manufactured with several layers. The FRP laminated circular tube induces the flexural failure instead of a bond-slip failure of the circular reinforced concrete piers under seismic induced lateral forces. To investigate the correctness and effectiveness of analytical solution derived in this study, the analytical results were compared with the experimental data and it was confirmed that the results were correlated well each other, The effects on the confinement of FRP laminated circular tube, such as the number of layers, the fiber orientations, and the mechanical properties, were investigated. From the parametric study, it was found that the number of layers, the fiber orientations, and the major Young's modulus (E11) of the FRP laminated circular tube were the dominant parameters affecting the confinement of reinforced concrete circular bridge piers.

• Journal of the Korea Concrete Institute
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• v.16 no.2 s.80
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• pp.249-260
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• 2004

The longitudinal steel connection of reinforced concrete bridge column is sometimes practically unavoidable, however the current Korean bridge design specifications have no special provisions about lap-splices of longitudinal steel. This paper reports experimental results of a research program investigating the seismic performance of circular RC bridge columns with respect to longitudinal steel connection detailing. Twenty-one circular column specimens were tested under quasi-static test. The columns with the entire longitudinal steel lap-spliced within plastic hinge region show relatively sudden strength degradation and low ductility than the columns with continuous longitudinal steel and the columns with half of longitudinal steel lap-spliced. However, the seismic performance of the column with mechanically connected longitudinal steel is similar to that of the column with continuous longitudinal steel. The final objectives of this study are to suggest appropriate longitudinal reinforcement connection details for the limited ductility design concept and to provide quantitative reference data and tendency for performance or damage assessment based on the performance levels such as cracking, yielding, collapse, etc. Ultimate displacement/drift ratio, displacement ductility, response modification factor, equivalent viscous damping ratio, residual deformation index, and effective stiffness are investigated and discussed in this paper.

• Journal of the Korea Concrete Institute
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• v.19 no.3
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• pp.265-273
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• 2007

The most common structural system for apartment buildings in Korea is adopted to combine structural systems: for example, a moment-resisting frame will be used for lower stories and bearing wall system for the upper stories. This type of buildings have soft and/or weak stories in lower stories, and it may lead to collapse of those buildings during the large earthquake. Reversed cyclic load tests were conducted to estimate the performance and behavioral characteristics of deep beam and exterior column Joints. Experimental parameter is the amount of transverse reinforcement (designed by ACI code and Sheikh's procedure). The results of this study are as follows: (1) The required transverse reinforcement of column designed by Sheikh's procedure requires 2.9 times larger than that designed by ACI procedure. Large amount of transverse reinforcement increase the ductility of the column. (2) Most of the lateral drift in the column is due to the flexural deformation in the joint and plastic hinge region and up-lift rotation. (3) Transverse reinforcement in the exterior column shall be required not only in the hinge region but also in the joint.

• Journal of the Korea Concrete Institute
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• v.25 no.3
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• pp.347-354
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• 2013

Recently, crushed fine aggregates are being widely used due to the shortage of natural sand. In Korea, the amount of fine particles under 0.08 mm contained in crushed fine aggregates is restricted to be less than 7%, which is similar to the regulations of ASTM but is still very strict compared to the regulations of the other nations. In addition, the crushed aggregates already have in them about 20% of fine particles under 0.08 mm which occurs while they are crushed. The fine particles are not easy to wash out, and also to maximize the use of resources it is deemed necessary to review the possibility of enhancing the limit of the amount of fine particles. Therefore, this study conducted experiments to analyze the characteristics of fine particles under 0.08mm and their influence on the properties of concrete. Experiments using silt and cohesive soil were also done for comparison. In the experiments on fine particles, the methylene blue value was more in the soil dust contained in silt and cohesive soil than in the stone powder contained in crushed fine aggregates. Also, the methylene blue value had a close correlation with packing density and liquid & plastic limit. In the experiments done with concrete, the quantity of high range water reducing agent demanded to obtain the same slump increased as the fine particle substitution rate heightened. However, in the experiment which used stone powder testing the compressive strength and tensile strength of concrete in the same water-cement ratio, there was little change in strength with less than 20% addition of fine particles among the fine aggregates, and no meaningful difference in the amount of drying shrinkage of concrete.

• Journal of Digital Convergence
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• v.16 no.2
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• pp.293-298
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• 2018

The aim of this study was to survey the effects of planned exercise over the age of 65 in male and female with regard to their self-efficacy, depression, and life satisfaction, based on the literatures of 14 master and doctoral dissertations published between 2004 and 2014. The subjects with program exercise habit were chosen considering the generalization of the physical characteristics of elderly subjects. The exercise duration was 50 minutes for 3 times a week for 12 to 24 weeks. Exercise intensity was an optimal aerobic exercise plan that the subjects themselves could perform. The average effect size of self-efficacy was 0.793 (26.1% increased), depression was -0.91(31.9% decreased), and life satisfaction was 1.506 (43.4% increased). These indicate that post-exercise psychological variables had a positive effect on self-efficacy and life satisfaction by lowering depression after regular exercise. Therefore, it is necessary to increase regular exercise participation and to provide sustainable scientific information for the aged and healthy living of the elderly.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.2 no.3
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• pp.1-13
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• 1982

Transition process of plastic region. displacements, stresses and strains ahead the flaw tips were analysed by the finite element method on the steel plate with the circular hole and the one with the elliptical hole under completely alternating load (repetition of tensile loading, unloading and compressive loading). As the results, the followings were obtained. Transition process of elastic failure (yielding) region was estimated. From this the tendency was confirmed that the fracture would be initiated from ahead the flaw tip, and propagated along the $45^{\circ}$ direction. The fundamental data available in estimating the stress intensity factor that was considered as the core in analysing the fracture mechanism of steel plates were obtained. It was indicated that when unloading after tension the effect of compressive loading, and even the compressive reyield, was occured ahead the flaw tip. Similarly it was indicated that when unloading after compression the effect of tensile loading, and even the tensile reyield, was occured ahead the flaw tip. It was considered that these phenomena were occured because the unloading effect was constrained by the residual strains when unloading. It was considered that the fatigue phenomenon was occured ahead, the flaw tip by repetition of tensile yield, the above compressive reyield, compressive yeild and the above tensile reyield. In addition, the tendency was confirmed that the fracture ahead the flaw tip was occured as the flaw was changed from the circular hole to the elliptical hole and became to be the crack lastly.