• Journal of Ocean Engineering and Technology
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• v.33 no.5
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• pp.411-420
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• 2019

It is essential to design crashworthy marine structures for operations in Arctic regions, especially ice-covered waters, where the structures must have sufficient capacity to resist iceberg impact. In this study, a numerical analysis of a colliding accident between an iceberg and stiffened plates was carried out employing the commercial finite element code ABAQUS/Explicit. The ice material model developed by Liu et al. (2011) was implemented in the simulations, and its availability was verified by performing some numerical simulations. The influence of the ambient temperature on the structural resistance was evaluated while the local stress, plastic strain, and strain energy density in the structure members were addressed. The present study revealed the risk of fracture in terms of steel embrittlement induced by ambient temperature. As a result, the need to consider the possibility of brittle failure in a plate-stiffener junction during operations in Arctic regions is acknowledged. Further experimental work to understand the structural behavior in a plate-stiffener junction and HAZ is required.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.6
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• pp.60-66
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• 2022

The optimal strain energy function was obtained by comparing the results of the analysis using the strain energy functions obtained by uniaxial tensile and equibiaxial tensile tests on gasket materials used in hydrogen fuel cells, with the results measured using a contact pressure measurement sensor. At this time, even when only the uniaxial tensile test was conducted, Yeoh could obtain the most accurate results even by conducting only the uniaxial tensile test. Using this, an analysis of the cross section of the gasket used in stack confirmed a safe contact pressure and no deformation on the separator. In the future, research will be conducted to verify the gasket durability by reliability evaluation.

• Journal of the Korean GEO-environmental Society
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• v.12 no.1
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• pp.61-70
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• 2011

The impact protection system consists of an arrangement of circular sheet pile cofferdams-denoted dolphin structuredeeply embedded in the seabed, filled with crushed rock and closed at the top with a robust concrete cap. Centrifuge model tests were performed to investigation the behaviors of dolphins in this study. Total 7 quasi-model tests and 11 dynamic model tests were performed. The main experimental results can be summarized as follows. Firstly, The experimental force-displacement results for quasi-static tests show a limited influence on the initial stiffness of the structure from the change in fill density and the related change in the stiffness of the fill. And by comparing the dissipation at the same dolphin displacement it was found that the denser fill increase the dissipation by 16% for the 20m dolphin and by 23% for the 30m dolphin. The larger sensitivity for the large dolphin is explained by a larger contribution to the dissipation from strain in the fill. In low level impacts the dynamic force-response is up to 26~58% larger than the quasi-static and the dissipation response is showed larger in small displacement. Hence, it is concluded conservative to use the quasi-static response characteristics in the approximation of the response, and it is further concluded that the dolphin resistance to low level impacts is demonstrated to be equivalent and even superior to the high level impacts.

• Composites Research
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• v.31 no.6
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• pp.332-339
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• 2018

Fiber metal hybrid laminate (FML) can be used as an economic material with superior mechanical properties and light weight than conventional metal by bonding of metal and FRP. However, there are disadvantages that it is difficult to predict fracture behavior because of the large difference in properties depending on the type of fiber and lamination conditions. In this paper, we study the failure behavior of hybrid materials with laminated glass fiber reinforced plastics (GFRP, GEP118, woven type) in Al6061-T6 alloy. The Al alloys were coated with GFRP 1, 3, and 5 layers, and fracture behavior was analyzed by using a static test and a low cycle fatigue test. In the low cycle fatigue test, strain - life analysis and the total strain energy density method were used to analyze and predict the fatigue life. The Al alloy did not have tensile properties strengthening effect due to the GFRP coating. The fatigue hysteresis geometry followed the behavior of the Al alloy, the base material, regardless of the GFRP coating and number of coatings. As a result of the low cycle fatigue test, the fatigue strength was increased by the coating of GFRP, but it did not increase proportionally with the number of GFRP layers.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.1
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• pp.107-114
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• 2017

A turbocharger is an engine supercharger that is driven by exhaust gas. It improves the output and fuel efficiency by increasing the charging efficiency of the mixture gas, which is achieved by changing the rotatory power of the turbine connected to the exhaust passage. It is important to control the supercharging for this purpose. A nozzle slide joint is one of the core parts. Austenitic stainless steel is currently used as the material for this part, and its excellent mechanical properties include high heat resistance and corrosion resistance. However, because of its poor machinability, there are many difficulties in producing products with complicated shapes. Machining is used in the production of nozzle slide joints for high dimensional accuracy after metal powder injection molding. As design variables in this study, we investigated the sintering temperature, product stress, deformation rate, radius of curvature of the punch, and angle of the chamfer punch, which are related to the strain and shapes. The goal is to suggest a forming process using Nitronic 60 that does not require machining to manufacture a nozzle slide joint for a turbocharger. Accordingly, we determined the best process environment using finite-element analysis, the signal-noise ratio, and the Taguchi method for experiment design. The relative density and hydrostatic pressure of the final product were in accordance with the results of the finite element analysis. Therefore, we conclude that the Taguchi method can be applied to the design process of metal powder injection molding.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.573-580
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• 2009

This paper presents the mix composition, production method, and curing condition applied to the extruded ECC(Engineered Cementitious Composite) panel which are able to exhibit multiple cracking and potential pseudo strain-hardening behavior. In addition to the production technique of extruded ECC panel, the effect of fiber distribution characteristics, which are uniquely created by applying extrusion process, on the flexural behavior of the panel is also focussed. In order to demonstrate fiber distribution, a series of experiments and analyses, including image processing/analysis and micro-mechanical analysis, was performed. The optimum mix composition of extruded ECC panel was determined in terms of water matrix ratio, the amount of cement, ECC powder, and silica powder. It was found that flexural behavior of extruded ECC panel was highly affected by the slight difference in mix composition of ECC panel. This is mainly because the difference in mix composition results in the change of micro-mechanical properties as well as fiber distribution characteristics, represented by fiber dispersion and orientation. In terms of the average fiber orientation, the fiber distribution was found to be similar to the assumption of two dimensional random distribution, irrespective of mix composition. In contrast, the probability density function for fiber orientation was measured to be quite different depending on the mix composition.