• Korean Journal of Materials Research
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• v.18 no.10
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• pp.547-551
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• 2008

Crack-free joining of $Si_3N_4\;and\;Al_2O_3$ using 15 layers has been achieved by a unique approach introducing Sialon polytypoids as a functionally graded materials (FGMs) bonding layer. In the past, hot press sintering of multilayered FGMs with 20 layers of thickness $500{\mu}m$ each has been fabricated successfully. In this study, the number of layers for FGM was reduced to 15 layers from 20 layers for optimization. For fabrication, model was hot pressed at 38 MPa while heating up to $1700^{\circ}$, and it was cooled at $2^{\circ}$/min to minimize residual stress during sintering. Initially, FGM with 15 layers had cracks near 90 wt.% 12H / 10 wt.% $Al_2O_3$ and 90 wt.% 12H/10 wt.% $Si_3N_4$ layers. To solve this problem, FEM (finite element method) program based on the maximum tensile stress theory was applied to design optimized FGM layers of crack free joint. The sample is 3-dimensional cylindrical shape where this has been transformed to 2-dimensional axisymmetric mode. Based on the simulation, crack-free FGM sample was obtained by designing axial, hoop and radial stresses less than tensile strength values across all the layers of FGM. Therefore, we were able to predict and prevent the damage by calculating its thermal stress using its elastic modulus and coefficient of thermal expansion. Such analyses are especially useful for FGM samples where the residual stresses are very difficult to measure experimentally.

• 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.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.19-26
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• 2021

The seismic isolation system have been applied in order to protect the collapse of bridge by seismic load and the vertical load transmitted from the superstructure. However, the failure and damages of non-shrinkage mortar, isolator and wedge in total 12 bridge were reported by Pohang Earthquake. In this study, the damage mechanism and behavior characteristics of elastomeric bearing by an earthquake were evaluated to consider the seismic isolation system including non-shrinkage mortar and the seat concrete of pier. To discuss the effect of installed wedge and damage mode of elastomeric bearing, the compressive-shear tests were carried out. Also, the mechanical behaviors and damage mechanism for each component of elastomeric bearing were evaluated by using finite element analysis. From the test results, the cracks were created at boundary between non-shrinkage mortar and seismic isolator and the shear loads were rapidly increased after bump into wedge. The cause for damage mechanism of seismic isolation system was investigated by comparing stress distribution of anchor socket and non-shrinkage mortar depending on wedge during earthquake.

• Journal of the Korea Convergence Society
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• v.10 no.1
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• pp.155-161
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• 2019

As composite is the light weight material whose durability and mechanical property are more superior than the existing general material. By taking notice of the composite with light weight, this study was about to investigate the static fracture characteristic of the bonded CFRP structure jointed with adhesive. Also, CFRP double cantilever beam with the variable of laminate angle was designed and the static fracture analysis was carried out. The laminate angles of CFRP double cantilever beam designed for this study were $30^{\circ}$, $45^{\circ}$ and $60^{\circ}$ individually. As the study result, the specimen with the laminate angle of $45^{\circ}$ was shown to have the durability better than those with the layer angles of $30^{\circ}$ and $45^{\circ}$. It was checked that the specimen with the laminate angle of $30^{\circ}$ had the weakest durability among all specimens. The damage data of the bonded CFRP structure by laminate angle could be secured through this study result. As the damage data of bonded interface obtained on the basis of this study result are utilized, the esthetic sense can be shown by being grafted onto the machine or structure at real life.

• Journal of the Mineralogical Society of Korea
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• v.31 no.4
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• pp.257-266
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• 2018

East China Sea (ECS) is known to be supplied with large amounts of sediments form Huanghe, Changjiang and various rivers in Korea. Many studies have been conducted to identify the effects of rivers and deposition process of ECS, but no consensus has been reached. In this study, clay minerals, rare earth elements (REEs) and grain size were analyzed to study the provenance and sedimentation environment of core 99MAP-P63 in ECS. Clay mineral contents of 99MAP-P63 are abundant in order of illite, chlorite, kaolinite, and smectite. The provenance of 99MAP-P63 sediments using clay minerals is interpreted as the Changjiang regardless of depth. As a result of REEs analysis, 99MAP-P63 sediments are very similar to Chinese rivers sediments. Therefore, the provenance of 99MAP-P63 is Changjiang, and the influence of Korean river seems to be insignificant. 99MAP-P63 sediments are generally classified as sandy silt, but the top of the core is divided into sand with a sand contents of 85 %. Compared with surrounding cores, sandy silt sediments arecorresponded to the low stand stage when sea-level was low, and the sediments were thought to have been supplied directly through the paleo-Changjiang. Sandy sediments in uppermost of core are corresponded to transgressive stage. Although distance from estuary was increased due to sea-level rise, it was possible to supply coarse sediments due to high bottom stress, and the paleo-Changjiang sediments deposited in study area were re-deposited.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.9
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• pp.175-181
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• 2019

In the case of a conventional single stage decompression regulator used for large depressurization in the hydrogen fuel cell system of a fuel cell electric vehicle (FCEV), problems can arise, such as pulsation, slow response, hydrogen brittleness, leakage, high weight, and high cost due to high decompression. Most of these problems can be overcome easily using two decompression mechanisms (two-stage structures). In addition, a wide outlet-pressure control range can be secured if an electronic solenoid is applied to the second decompression. Accordingly, it is necessary to improve the precision of the outlet pressure of a two-stage pressure-reducing regulator and develop techniques, such as leakage prevention, durability, light weight, and price reduction. Therefore, to improve the outlet pressure accuracy and prevent leakage, the structural part before and after decompression to improve the air tightness were divided and the analysis was carried out assuming that the valve part was closed (open ratio: 0%) after each initial internal pressure application.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.2
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• pp.237-243
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• 2019

Floating platforms made of PE (PolyEthylene) are often located in shallows of seas, rivers or lakes. They are widely used for marine pensions, marine pontoons, marine bridges, etc. These products are characterized by good flexibility, recyclability, chemical resistance and weatherability with corrosion resistance. Existing PE floating platforms have a simple structure in which one pipe is fastened to one bracket, but this has limited application, even if a user modifies the arrangement. Therefore, we developed a structure that allows buoyancy pipes of various sizes to be fastened to one bracket and verified the structural safety of the product using the finite element method. From the results of structural analysis for buoyancy pipes of different diameters, the maximum stress ratio was 0.78 compared with allowable criteria of 1.0, which represented sufficient safety for a model with 500 mm diameter pipes. Based on the results of this study, further research to evaluate the structural safety of various floating platforms can be carried out in the further; it will also be necessary to establish related evaluation criteria.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.4
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• pp.632-638
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• 2022

As Korean coastal activity is high, the incidence of accidents caused by marine waste is extensive. An accident in which marine floating waste ropes and fishing nets are wound around the propeller of a sailing ship is termed "Rope wrapped accident." To prevent such accidents, this study applied the Finite Element Method (F.E.M.) for performance evaluation of the shaver type cutter, commercialized in Korea, through a structural safety review and water tank test. The results demonstrate that all parts constituting the rope cutter were damaged before reaching 0.5s, and the safety factor of each part was found to be at least 2 based on the maximum stress generated compared to the tensile strength. In the basin test, the cutting process of the shaver type rope cutter was reviewed, and the installation angle was set for each case considering that the rope floating in the sea actually enters at various angles. Consequently, as it was successful at cutting in all the cases, it can be concluded that there will be no problem in cutting the rope regardless of the mounted angle of the cutting blade.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.561-577
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• 2021

The compacted bentonite buffer in a geological repository for high-level radioactive waste disposal is saturated due to groundwater inflow. Saturation of the bentonite buffer results in bentonite swelling and bentonite penetration into the rock discontinuities present around the disposal hole. The penetrated bentonite is exposed to groundwater flow and can be eroded out of the repository, resulting in bentonite mass loss which can affect the physical integrity of the engineered barrier system. Hence, the evaluation of buffer-rock interactions and coupled behavior due to groundwater inflow and bentonite penetration is necessary to ensure long-term disposal safety. In this study, the effects of the bentonite penetration and swelling on the physical properties of jointed rock mass were evaluated using the quasi-static resonant column test. Jointed rock specimens with bentonite penetration were manufactured using Gyeongju bentonite and hollow cylindrical granite rock discs obtained from the KAERI underground research tunnel. The effects of vertical stress and saturation were assessed using the P-wave and S-wave velocities for intact rock, jointed rock and jointed rock with bentonite penetration specimens. The joint normal and joint shear stiffnesses of each joint condition were inferred from the wave velocity results assuming an equivalent continuum. The joint normal and joint shear stiffnesses obtained from this study can be used as input factors for future numerical analysis on the performance evaluation of geological waste disposal considering rock discontinuities.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.4
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• pp.537-548
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• 2022

It is important to design the pavement thickness considering heavy-duty traffic loads, which can cause excessive stress and strain in the pavement. Port-rear roads and industrial roads have many problems due to early stress in pavement because these have a higher ratio of heavy loads than general roads such as national roads and expressways. Internationally, composite pavement has been widely applied in pavement designs in heavy-duty areas. Composite pavement is established as an economic pavement type that can increase the design life by nearly double compared to that of existing pavement while also decreasing maintenance and user costs. This study suggests a thickness design method for composite pavement using roller-compacted concrete as a base material to ensure long-term serviceability in heavy-duty areas such as port-rear roads and industrial roads. A three-dimensional finite element analysis was conducted to investigate the mechanical behavior and the long-term pavement performance ultimately to suggest a thickness design method that considers changes in the material properties of the roller-compacted concrete (RCC) base layer. In addition, this study presents a user-friendly catalog design method for RCC-base composite pavement considering the concept of linear damage accumulation for each container trailer depending on the season.