• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.6
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• pp.29-37
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• 2016

This paper proposes a shape optimization of the metal boss for a composite motor case using finite element analysis. For the structural safety and the weight reduction of the composite motor case, under the internal pressure, the fiber stress in the dome area and the tightening bolt stress are constrained and the boss weight is set to objective function, respectively. The response surface models are constructed for the performance characteristics by using response surface method. The significance of the design variables about the performance characteristics is evaluated through the ANOVA(analysis of variance) and the goodness of fit test for the constructed model is performed through the regression analysis. The SQP(sequential quadratic programming) algorithm is used for the optimization and the proposed method is verified by performing structural analysis for the optimum shape.

• Steel and Composite Structures
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• v.19 no.5
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• pp.1203-1219
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• 2015

'Distortional buckling' is one of the predominant buckling types that may occur in a steel-concrete composite box beam (SCCBB) under a negative moment. The key factors, which affect the buckling modes, are the torsional and lateral restraints of the bottom plate of a SCCBB. Therefore, this article investigates the equivalent lateral and torsional restraint rigidity of the bottom plate of a SCCBB under a negative moment; the results of which show a linear coupling relationship between the applied forces and the lateral and/or torsional restraint stiffness, which are not depended on the cross-sectional properties of a SCCBB completely. The mathematical formulas for calculating the lateral and torsional restraint rigidity of the bottom plate can be used to estimate: (1) the critical distortional buckling stress of SCCBBs under a negative moment; and (2) the critical distortional moment of SCCBBs. This article develops an improved calculation method for SCCBBs on an elastic foundation, which takes into account the coupling effect between the applied forces and the lateral and/or torsional restraint rigidity of the bottom plate. This article analyzes the accuracy of the following calculation methods by using 24 examples of SCCBBs: (1) the conventional energy method; (2) the improved calculation method, as it has been derived in this article; and (3) the ANSYS finite element method. The results verify that the improved calculation method, as it has been proved in this article, is more accurate and reliable than that of the current energy method, which has been noted in the references.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.5
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• pp.445-452
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• 2017

The wing leading edge skin in this research is an essential structural factor for improving wings' aeromechanical functions, protecting the interior elements of the wings from external damage including birds, and navigating planes safely. The study compared and reviewed models manufactured for optimal light-weight wings of composite UAVs. It compared and investigated displacement forms of torsion loads through finite element analysis using MSC. Patran/Nastran. By confirming the improvement of light-weighting performance according to lamination type, thickness change and shape through torsion strength tests of each model, the research suggested the optimal light-weight wing leading edge skin for small composite UAVs.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.5
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• pp.381-387
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• 2017

Fiber-reinforced composites not only have a direction of thermal expansion coefficient, but also inevitably suffer thermal stress effects due to the difference between the manufacturing process temperature and the actual use temperature. The damage caused by thermal stress is more prominent in the case of thick composite laminates, which are increasingly applied in the aerospace industry, and have a great influence on the mechanical function and fracture strength of the laminates. In this study, the dimensional reduction and thermal stress recovery theory of composite beam structure having high slenderness ratio is introduced and show the efficiency and accuracy of the thermal stress comparison results between the 3-D finite element model and the dimension reduction beam model. Efficient recovery analysis study will be introduced by reconstructing the thermal stress of the composite beam section applied to the thermal environment by constructing the dimensional reduction modeling and recovery relations.

• Journal of the Korean Geosynthetics Society
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• v.19 no.1
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• pp.35-44
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• 2020

Design techniques for the deep mixing method, one of the soft ground improvement methods, include two ways to interpret the ground as composite ground and pile ground. However, since comparative studies on these two approaches are insufficient, it is difficult to clearly define the analysis criteria in the design. In this study, two-dimensional and three-dimensional analyses have been performed with different conditions. The three conditions, the embankment height, depth of soft ground, and replacement ratio of reinforcement zones were varied and the analysis was performed on the basis of the assumption of composite ground and pile ground for each condition. As a result, the minimum depth of improvement in the two-dimensional analysis was deeper by 6.85~9.08% than in the three-dimensional analysis. The pile ground analysis showed that the depth of improvement was deeper by 12.22~14.45% than the composite ground analysis. Based on these results, it is concluded that for more accurate design, three-dimensional analysis should be performed rather than two-dimensional analysis. also, it is judged that necessary to analyze the ground as composite ground for economical design, and as the pile ground analysis for stable design.

• Journal of Hydrogen and New Energy
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• v.22 no.6
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• pp.859-867
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• 2011

The cold start problem is one of major obstacles to overcome for the commercialization of fuel cell vehicles. However, the cold start characteristics of fuel cell systems are very complicated since various phenomena, i.e. ice-blocking, electro-chemical reactions, heat transfer, and defrosting of BOP components, are involved in them. This paper presents a framework to approach the problem at a full stack scale using Axiomatic Design (AD). It was characterized in terms of Functional Requirements (FRs) and Design Parameters (DPs) while their relations were established in a design matrix. Considering the design matrix, the endplates should have low thermal conductivity and capacity without increase in weight or decrease in structural stiffness. Consequently, composite sandwich endplates were proposed and examined both through finite element analyses and experiments simulating cold start conditions. From the examinations, it was found that the composite sandwich endplates significantly contributed to improving the cold start characteristics of PEMFC.

• Composites Research
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• v.23 no.6
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• pp.14-18
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• 2010

Among the factors that threaten spacecraft, Micrometeoroid and Orbital Space Debris(MMOD) cause damage to spacecraft and impact velocity is about 8~70km/s. Nowadays, various Whipple Shield are studied and applied to protect spacecraft. As the materials used to Shielding System, aluminum is usually used but composite is also used increasingly. So this study compared characteristics of hypervelocity impact of Aluminum and composites through finite element analysis. The Projectile was a spherical shape using Aluminum 2017-T4, and aluminum plate was using Aluminum 6061-T6, CFRP plate was using T300/5208. Initial impact velocity of projectile was 1km/s. As a result, kinematic energy of projectile decreased to about 64J and about 63J for aluminum plate and CFRP plate, respectively after impact. Although both results is almost same about the absorption of impact energy, you can think the CFRP has good ballistic characteristic, because CFRP is lighter about 1.7 times compared with density of aluminum.

• Steel and Composite Structures
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• v.22 no.3
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• pp.537-565
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• 2016

Australian railway networks possess a large amount of aging timber components and need to replace them in excess of 280 thousands $m^3$ per year. The relatively high turnover of timber sleepers (crossties in a plain track), bearers (skeleton ties in a turnout), and transoms (bridge cross beams) is responsible for producing greenhouse gas emissions 6 times greater than an equivalent reinforced concrete counterparts. This paper presents an innovative solution for the replacement of aging timber transoms installed on existing railway bridges along with the incorporation of a continuous walkway platform, which is proven to provide environmental, safety and financial benefits. Recent developments for alternative composite materials to replace timber components in railway infrastructure construction and maintenance demonstrate some compatibility issues with track stiffness as well as structural and geometrical track systems. Structural concrete are generally used for new railway bridges where the comparatively thicker and heavier fixed slab track systems can be accommodated. This study firstly demonstrates a novel and resilient alterative by incorporating steel-concrete composite slab theory and combines the capabilities of being precast and modulated, in order to reduce the depth, weight and required installation time relative to conventional concrete direct-fixation track slab systems. Clear benefits of the new steel-concrete composites are the maintainability and constructability, especially for existing railway bridges (or brown fields). Critical considerations in the design and finite element modelling for performance benchmarking of composite structures and their failure modes are highlighted in this paper, altogether with risks, compatibilities and compliances.

• Structural Engineering and Mechanics
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• v.55 no.4
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• pp.765-784
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• 2015

Connections are usually designed either as pinned usually associated with simple construction or rigid normally is associated with continuous construction. However, the actual behaviour falls in between these two extreme cases. The use of partial strength or semi-rigid connections has been encouraged by Euro-code 3 and studies on semi-continuous construction have shown substantial savings in steel weight of the overall construction. Composite connections are proposed in this paper as partial or full strength connections. Standardized connection tables are developed based on checking on all possible failure modes as suggested by "component method" for beam-to-column composite connection on major axis. Four experimental tests were carried out to validate the proposed standardised connection table. The test results showed good agreement between experimental and theoretical values with the ratio in the range between 1.06 to 1.50. All tested specimens of the composite connections showed ductile type of failure with the formation of cracks occurred on concrete slab at maximum load. No failure occurred on the Trapezoidal Web Profiled Steel Section as beam and on the British Section as column.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.7
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• pp.988-991
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• 2012

The computer simulation was performed to confirm distribution of current and power density according to inner diameter of graphite mold of SPS(Spark Plasma Sintering). When the inner diameters of a graphite mold are varied $10mm{\Phi}$, $20mm{\Phi}$, $30mm{\Phi}$ and $40mm{\Phi}$, the more the inner diameter of graphite mold is decreased, the more the current density of punch section is increased. Because the electrical resistivity of the SiC-$ZrB_2$ specimen section($7.77{\times}10^{-4}{\Omega}{\cdot}cm$) was lower than the electrical resistivity($6.00{\times}10^{-3}{\Omega}{\cdot}cm$) of graphite section, the current density and power density of specimen section was higher than those of graphite section. It is considered that a SiC-$ZrB_2$ composite is sintered by more Joule heat of specimen section than that of mold and punch section. The current and power density distribution of a SiC-$ZrB_2$ composite can be predicted through computer simulation when SPS is conducted, and an electrical resistivity of the SiC-$ZrB_2$ composite is main element of SPS.