• Journal of The Geomorphological Association of Korea
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• v.21 no.4
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• pp.109-120
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• 2014

This study is an analysis on gravel and sand of sand-gravel bar that stretches variously in the Duchon stream basin, which is one of Hong-Cheon River(a well-developed sand-gravel bar in upstream river)'s upper stream basin. The purpose of this study was to understand the characteristic of the stream's topographic development that variously occur in the small basin by comparing the differences between the aspects of development and the sediment of sand-gravel bar in each section and by examining the transition of sediments moving from upstream to downstream. Through the analysis on the roundness and flatness of gravel, we observed an irregular trend following the increase in supply of granite gravel and gneiss gravel as we traveled downstream. As for the aspect of change in sand's grain size, the overall ratio of medium-coarse sand was very high, but the results showed no big difference in the change following the inflow of stream from the main stream section to the gneiss and granite zone.

• Journal of the Korea Concrete Institute
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• v.11 no.6
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• pp.35-46
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• 1999

The steel fiber reinforced concrete may affect substantially to the tension stiffening at post cracking behavior. Even if several tension stiffening models exist, they are for plain and normal strength concrete. Thus, the development of tension stiffening models for steel fibrous high strength RC members are necessary at this time when steel fiber reinforced and high strength concretes are common in use. This paper presents tension stiffening effects from experimental results on direct tension members with the main variables such as concrete strength, concrete cover depth, steel fiber quantity and aspect ratio. The comparison of existing models against experimental results indicated that linear reduced model closely estimated the test results at normal strength level but overestimated at high strength level. Discontinuity stress reduced model underestimated at both strength levels. These existing models were not valid enough in applying at steel fibrous high strength concrete because they couldn't consider the concrete strength nor section area. Thus, new tension stiffening models for high strength and steel fiber reinforced concrete were proposed from the analysis of experimental results, considering concrete strength, rebar diameter, concrete cover depth, and steel fiber reinforcement.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.3 s.180
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• pp.47-55
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• 2006

Laser welding of dissimilar metals has been widely used to improve a wear resistance and a corrosion resistance of the industrial parts. The objective of this research is to investigate the influence of the process parameters, such as the welding for SM45C and STS304 with CW Nd:YAG lasers. The bead-on-plate welding tests are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the dissimilar welding, the welding quality of the cut section, stress-strain behavior and the hardness of the welded metal are investigated. From the results of the investigation, it has been shown that the optimal voiding condition without defects in the vicinity of the welded area and with a good welding quality is 1600W of the laser power, 0.85m/min of welding speed and $4{\ell}/min$ of pressure for shielding gas.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.230-235
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• 2003

In the micro hole punching, the size and shape of burr and burnish zone are very important factors to evaluate quality of micro holes which depend on punch-die clearance, stain rate, workpiece material and etc. To get micro holes with small burr and wide burnish zone for industrial demands, not only the parametric study but also a study on fracture behavior in shear band are necessary. In this study, 100 $\mu\textrm{m}$, 25 $\mu\textrm{m}$ micro holes in diameter were fabricated on brass (Cu63/Zn37) and SUS 316 foils as aspect ratio 1:1, and the characteristics of micro holes was investigated comparing with man holes over several mm by scanning electron microscopic views and section views. Like macro hole, micro hole is also composed of 4 portions, rollover, burnish zone, fracture zone and it shows similar fracture behavior in shear band, but？ by high strain rate (10$^2$∼ 10$^3$s$\^$-1/) unlike macro hole fabrication and increment of relative grain size several different results are shown.

• Journal of the Korean Society for Advanced Composite Structures
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• v.6 no.3
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• pp.26-31
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• 2015

The domestic and foreign specifications presented the effective width based on flange length to width ratio only. The existing paper on the effective width grasped of the effect of span, load type and cross-section properties, but localized steel bridges. Recently, The studies are going on in progress for the application of fiber reinforced composite material in construction field. Therefore, it is required to optimum design that have a good grasp the deformation characteristic of the displacements and stresses distribution and predict variation of the effective width for serviceability loading. This research addresses the effective width of all composite material box girder bridges using the finite element method. The characteristics of the effective width of composite structures may vary according to several causes, e.g., change of fibers, aspect, etc. Parametric studies were conducted to determine the effective width on the stress elastic analysis of all composite materials box bridges, with interesting observations. The various results through numerical analysis will present an important document for construct all composite material bridges.

• Transactions of Materials Processing
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• v.12 no.4
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• pp.314-319
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• 2003

In the micro hole punching, the size and shape of burr and burnish zone are very important factors to evaluate quality of micro holes which depend on punch-die clearance, strain rate, workpiece material and etc. To get micro holes with small burr and wide burnish zone for industrial demands, not only the parametric study but also a study on fracture behavior in shear band are necessary. In this study, 100 $\mu$m, 25 $\mu$m micro holes in diameter were fabricated on brass (Cu63/Zn37) and SUS 316 foils as aspect ratio 1:1, and the characteristics of micro holes was investigated comparing with those of macro holes over several mm by scanning electron microscopic views and section views. Like macro hole, micro hole is also composed of 4 portions, rollover. burnish zone, fracture zone and burr, and it shows similar fracture behavior in shear band. But by high strain rate (10$^2$∼10$^3$s$^{-1}$ ) condition unlike that of macro hole fabrication and by the increment of relative grain size in the direction of the workpiece thickness, fracture zone is not observed.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2010.04a
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• pp.67-67
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• 2010

이미지를 이용한 도공층 구조 분석은 도공층의 실제 Morphology를 분석하여 평가하는 방법으로서 최근 세밀한 도공층 구조 분석을 위해 이 방법에 대한 많은 연구가 진행되고 있다. 특히 이러한 방법은 수은압입법(Mercury intrusion)이나 질소흡착법 (Nitrogen adsorption by BJH theory) 등과 같은 기존의 공극 특성 평가 방법과 달리 pore aspect ratio 및 orientation 등과 같은 공극 dimension을 평가할 수 있는 장점이 있다. 이러한 공극 dimension은 size distribution 및 porosity와 더불어 인쇄, 라미네이션 접착 등과 같은 Liquid interfacial 및 침투 측면에서 중요한 요소이기 때문에 이를 평가하기 위한 적합한 방법으로 인식되고 있다. 또, 원지 부분과 도공층 간의 경계를 명확하게 보여주고 Surface와 Cross-section 영역을 구분하여 평가 할 수 있어 더 명확한 평가를 가능하게 한다. 본 연구에서는 이미지 분석을 통해 도공액 구성 조건에 따른 도공층의 공극 구조 특성을 평가 하였고 일부 요소에 대해서는 수은 압입법과 비교 평가하여 이미지 분석법과의 상관성에 대해 고찰 하였다. 본 연구에서 사용된 FE (Field Emission)-SEM은 일반 SEM과 달리 전압에 의한 높은 전기장의 형성을 통해 저 가속 전압으로 이미지를 구현하는 장비로서 본 연구에서는 FE-SEM을 통해 도공층의 세밀한 Morphology와 공극 구조 이미지를 구현할 수 있었다.

• Structural Engineering and Mechanics
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• v.53 no.5
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• pp.981-995
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• 2015

This paper presents a finite element procedure for dynamic analysis of non-uniform Timoshenko beams made of axially Functionally Graded Material (FGM) under multiple moving point loads. The material properties are assumed to vary continuously in the longitudinal direction according to a predefined power law equation. A beam element, taking the effects of shear deformation and cross-sectional variation into account, is formulated by using exact polynomials derived from the governing differential equations of a uniform homogenous Timoshenko beam element. The dynamic responses of the beams are computed by using the implicit Newmark method. The numerical results show that the dynamic characteristics of the beams are greatly influenced by the number of moving point loads. The effects of the distance between the loads, material non-homogeneity, section profiles as well as aspect ratio on the dynamic responses of the beams are also investigated in detail and highlighted.

• Journal of Industrial Technology
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• v.26 no.B
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• pp.111-118
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• 2006

The reinforced concrete structure is one of the most popular structures in real construction. Concrete has been strengtened rapidly due to the development of new material and construction technology. But as the concrete has been getting stronger, the brittleness of material has increased and the better ductility has been required. So, the study for strengthening stiffener has been urgently needed. As we said above, it is expected that the use of high strength steel and concrete will be increased. However, The experimental data is not enough for solving problems of the use of high strengthened steel and concrete. In this research, we analyzed 45 combinations of the strength levels of concrete, the thickness of material and the steel strength with regard to simple Reinforced Concrete SLAB Beam bridge. The program MIDAS CIVIL was used to find the optimal combination. As a result, it was found that strength ratio per unit section is in inverse proportion to the strength of material and that the strengths of steel are respectively 400 MPa for low strengthened concrete and 300 MPa for high strengthened concrete. For economic aspect and usability, the effect of high strength steel is not as high as we expected it would be.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.6
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• pp.825-832
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• 2010

The objective of this study is to investigate flow behaviors of polluted air in order to prevent the impact of disaster in a tunnel. This paper presents the experimental results qualitatively in terms of flow characteristics in two kinds of rectangular tunnel models in which each distance from the centerline above the inlet vent to the exhaust vent is 0 and 60 mm, respectively. The olive oil is used as the tracer particles. The flow is tested at the flow rate of $14.16{\times}10^{-4}\;m^3/s$ and the inlet vent velocity of 1.1 m/s with the kinematic viscosity of air. The aspect ratio of the model test section is 10. The average velocity vectors, streamlines, and vorticity distributions are measured and analyzed by the Flow Manager in a particle image velocimetry(PIV) system. The PIV technology gives three different velocity distributions according to observational points of view for understanding the polluted air flow characteristics. The maximum value of mean velocity generally occurs in the inlet and outlet vent regions in the tunnel models.