• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.696-701
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• 2016

Multi-stage deep drawing is a widely used industrial manufacturing process, and its applications are gradually expanding to both small products and large metallic products. The USB C-type socket used in smart phones, for example, is manufactured using oval multi-stage deep drawing. The socket is very small and slender and it requires precise manufacturing. The thickness distribution of the final product is guaranteed only if it is uniform throughout the overall process. Therefore, minimizing the height difference between long and short sidewalls after the first operation is important for this goal. An initial blank optimization was performed for an oval-type drawing process based on finite element simulations. The goal was to determine an initial blank geometry that can maintain uniform height and thickness after the first draw operation. The initial blank shape of the sheet metal was optimized, and the results show that it satisfied the conditions of minimal thickness reduction and even thickness distribution. The geometry from the optimized simulation was compared with experimental results, which showed good agreement.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.3
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• pp.185-196
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• 2006

Fracture toughness is a material property for crack initiation and propagation in fracture mechanics. For mode I fracture toughness measurement in concrete, RILEM committees 89-FMT proposed three-point bend tests based on the two-parameter fracture model. But, there is no proposed test method as a standard for mixed mode test for now. And RILEM three-point bend test procedure is complicate. Therefore, in this study, brazilian disks of various size were designed as the concrete with a similar specified concrete strength and maximum size of coarse aggregate($G_{max}$) were respectively 20mm and 40mm. And mode I fracture toughness of brazilian disks was compared with that of RILEM three-point bend test. As a result, it was suggested appropriate size(thickness, diameter) and notch length ratio of brazilan disk on the $G_{max}$. And it was verified that stress intensity factors for mixed mode can be easily calculated with the disk specimen. Stress intensity factors of a concrete brazilian disk were evaluated with finite element analysis and five terms approximation for comparison.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.6 s.58
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• pp.176-182
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• 2009

Other damage can occur due to the preexisting dull structure and installation of nonenvironmental-friendly concrete structure, lack of function for preventing coastal erosion. Increase of personal income and fast spread of the concept of waterfront casued the initiation of many project to improve aging coastal ports. However, none of environment-friendly structure has been developed and pre-existing solid block, igloo block, tunnel block are used commonly. In piers and lighter's wharf where the ships are mooring, resonance by the generation of a reflected wave caused by penetration wave in the port and port wave increases wave heights in the port and makes difficult to maintain the temperature, causes problems in mooring ships and cargo-working, and eventually increase the occurance of damages of the small ships by the collision. Therefore, development of new types of blcok is necessary. To apply Coastal Environments block developed for this reason, it requires allowable bearing capacity evaluation of shear key. For this study, we made test specimen for connecting part of C.E. Block, and conducted friction test of boundary surface. Data obtained by the experiment was analyzed by finite element analysis and assessed the coefficient of friction between C.E. Block and boundary surface.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.271-278
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• 2019

The corrosion of reinforcements embedded in concrete causes severe deterioration in reinforced concrete structures. As a countermeasure, epoxy coated reinforcements are used to prevent corrosion of reinforcements. When epoxy coated bars are used, the resistance of corrosion is excellent, but epoxy coating on the bars have a disadvantage of reduction in bond capacity comparing to that of normal bars. Therefore, it is necessary to confirm the bond performance of epoxy coated reinforcements through experimental and analytical methods. Bond behaviors of epoxy coated bars for various diameters of 13 and 19mm and thicknesses of cover concrete of 3 types(ratio of cover to bar diameter) are examined. As the diameters of the epoxy coated bars increase, the difference of bond strength between epoxy coated and uncoated bars also increases and damage patterns showed pull out failure. In addition, finite element analysis was performed based on the bond-slip relationship obtained by direct pullout test and compared with the flexural test results. It is considered that flexural member test is more useful than pullout test for simulating the behavior of actual structure.

• Geophysics and Geophysical Exploration
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• v.6 no.4
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• pp.165-170
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• 2003

Recently, resistivity surveys have been frequently carried out over the irregular terrain such as mountainous area. Such an irregular terrain itself can produce significant anomalies which may lead to misinterpretations. In this study, topographic effects in resistivity survey were studied using the physical scale modeling as well as the numerical one adopting finite element method. The scale modeling was conducted at a pond, so that we could avoid the edge effect, the inherent problem of the scale modeling conducted in a water tank in laboratory. The modeling experiments for two topographic features, a ridge and a valley with various slope angles, confirmed that the results by the two different modeling techniques coincide with each other fairly well for all the terrain models. These experiments adopting dipole-dipole array showed the distinctive terrain effects, such that a ridge produces a high apparent resistivity anomaly at the ridge center flanked by zones of lower apparent resistivity. On the other hand, a valley produces the opposite anomaly pattern, a central low flanked by highs. As the slope of a terrain model becomes steeper, the terrain-induced anomalies become stronger, and moreover, apparent resistivity can become even negative for the model with extremely high slope angle. All the modeling results led us to the conclusion that terrain effects should be included in the numerical modeling and/or the inversion process to interpret data acquired at the rugged terrain area.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.993-999
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• 2008

A girder height limitation is the critical parameter for rapid construction of bridge deck and construction space limitation especially in urban area such as high population area and high density habitats. A standard post-tensioned I-shaped concrete girder usually demands relatively higher girder height in order to retain sufficient moment arm between compression force and tensile force. To elaborate this issue, a small U-shaped section with wide flanges can be used as a possible replacement of I-shaped standard girder. This prestressed concrete box girder allows more flexible girder height adjustment rather than standard I-shaped post-tensioned girder plus additional torsion resistance benefits of closed section. A 30m-long, 1.7m-high and 3.63m-wide actual small prestressed concrete box girder is designed and a laboratory test for its static behaviors by applying 6,200kN amount of load in the form of 4-point bending test was performed. The load-deflection curve and crack patterns at different loading stage are recorded. In addition, to extracting the dynamic characteristics such as natural frequency and damping ratio of this girder, several excitation tests with artificial mechanical exciter with un-symmetric mass are carried out using operational frequency sweep-up. Nonlinear finite element analysis of this 4 point bending test under monotonic static load is investigated and discussed with aids of concrete damaged plasticity formulation using ABAQUS program.

• Journal of the Korean Society for Railway
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• v.16 no.3
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• pp.207-216
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• 2013

The components of concrete track (rail and rail fastening system) in railway bridge deck ends are damaged and deteriorated by track-bridge interaction forces such as uplift forces and compression forces owing to their structural flexural characteristics (bridge end rotation). This had led to demand for alternatives to improve structural safety and serviceability. In this study, the authors aim to develop a transition track to enhance the long term workability and durability of concrete track components in railway bridge deck ends and thereby improve the performance of concrete track. A time-history analysis and a three-dimensional finite element method analysis were performed to consider the train speed and the effect of multiple train loads and the results were compared with the performance requirements and German standard for transition track. Furthermore, two specimens, a normal concrete track and a transition track, were fabricated to evaluate the effects of application of the developed transition track, and static tests were conducted. From the results, the track-bridge interaction force acting on the track components (rail displacement, rail stress, and clip stress) of the railway bridge deck end were significantly reduced with use of the developed transition track compared with the non-transition track specimen.

• Journal of the Korean Magnetics Society
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• v.25 no.5
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• pp.162-168
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• 2015

The ${\mu}$-turn coil having a width of ${\mu}m$ on the GMR-SV (giant magnetoresistance-spin valve) device based on the antiferromagnetic IrMn layer was fabricated by using the optical lithography process. In the case of GMR-SV film and GMR-SV device, the magnetoresistance ratios and the magnetic sensitivities are 4.4%, 2.0%/Oe and 1.6 %, 0.1%/Oe, respectively. In the y-z plane the distribution of magnetic field of GMR-SV device and $10{\mu}$-turns coil which put under the several magnetic bead(MB)s with a diameter of $1{\mu}m$ attached to RBC (red blood cell) was analyzed by the computer simulation using the finite element method. When the AC currents of 20 kHz from 0.1 mA to 10.0 mA flow to the 10 turns ${\mu}$-coil, the magnetic field at the position of $z=0{\mu}m$ at the center of coil was calculated from $30.1{\mu}T$ to $3060{\mu}T$ in proportion to the current. The magnetic field at the position of $z=10{\mu}m$ was decreased to one-sixth of that of $z=0{\mu}m$. It was confirmed that the $10{\mu}$-turn coil having enough magnitude of magnetic field for the capture of RBC is possible to use as a biosensor for the detection of magnetic beads attached to RBC.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.3
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• pp.97-103
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• 2011

In this research, a small-scaled laboratory test and FEM analysis have been carried out to evaluate the feasibility of field construction with couple of recycled materials, such as in-situ soil, water-treatment sludge, and crumb rubbers. A static loading, which simulates the real traffic load, was adopted in lab test. The test was carried out, according to simulated field construction stages, such as excavation, bedding materials and pipe installation, placing and curing of controlled low strength materials, and simulated traffic loading. Couple of measuring instruments were adopted. The maximum vertical and horizontal deformations were 0.83% and 1.09%, during placing the CLSM. The measured vertical and horizontal deformations with curing time were 0.603mm and 0.676mm, respectively. The reduction effect of vertical and lateral earth pressure was relatively big. Also, FEM analysis was carried out to get the deformation, earth pressure and strain of PVC with different Controlled Low Strength Materials(CLSM) materials.

• Journal of the Society of Disaster Information
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• v.17 no.4
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• pp.747-754
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• 2021

Purpose: Seismic safety evaluation of a curved bridge must be performed since the curved bridges exhibit the complex behavior rather than the straight bridges, due to geometrical characteristics. In order to conduct the probabilistic seismic assessment of the curved bridge, Seismic fragility evaluation was performed using the uncertainty of the steel material properties of a curved bridge girde, in this study. Method: The finite element (FE) model using ABAQUS platform of the curved bridge girder was constructed, and the statistical parameters of steel materials presented in previous studies were used. 100 steel material models were sampled using the Latin Hypercube Sampling method. As an input ground motion in this study, seismic fragility evaluation was performed by the normalized scale of the Gyeongju earthquake to 0.2g, 0.5g, 0.8g, 1.2g, and 1.5g. Result: As a result of the seismic fragility evaluation of the curved girder, it was found that there was no failure up to 0.03g corresponding to the limit state of allowable stress design, but the failure was started from 0.11g associated with using limit state design. Conclusion: In this study, seismic fragility evaluation was performed considering steel materials uncertainties. Further it must be considered the seismic fragility of the curved bridge using both the uncertainties of input motions and material properties.