• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.1
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• pp.121-127
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• 2013

With the continuing demand for lightweight bicycles, carbon fiber composite materials have been widely used in manufacturing bicycle frames and components. Unlike general isotropic materials, the structural characteristics of composite materials are strongly influenced by the staking directions and sequences of composite laminates. Thus, to verify the design process of bicycles manufactured using composites, structural analysis is considered essential. In this study, a carbon-fiber-reinforced plastic (CFRP) bicycle frame was designed and its structural behavior was investigated using finite element analysis (FEA). By measuring the failure indices of the fiber and matrix under various stacking sequences and loading conditions, the effect of the stacking condition of composite laminates on the strength of the bicycle structure was examined. In addition, the structural safety of the bicycle frame can be enhanced by reinforcing weak regions prone to failure using additional composite laminates.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.7
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• pp.592-600
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• 2007

Nowadays, researches for replacing material systems for cryotanks by composites have been being performed for the purpose of lightweight launch vehicle. In this paper, a type 3 propellant tank, which is composed of the composite developed for cryogenic use and an aluminum liner, was fabricated and tested considering actual operating environment, that is, cryogenic temperature and pressure. For this aim, liquid nitrogen (LN2) was injected into the fabricated tank and in turn, gaseous nitrogen (GN2) was used for pressurization. During this test procedure, strains and temperatures on the tank surface were measured. The delamination between hoop layer and helical one, was detected during the experiment. Several attempts were followed to investigate the cause analytically and experimentally. Thermo-elastic analysis in consideration of the progressive failure was done to evaluate the failure index. Experimental approach through a LN2 immersion test of composite/aluminum ring specimens suitable for simulating the Type 3 tank structure.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.121-124
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• 2008

The purpose of this study is to evaluate the critical strengthening ratio of concrete railroad bridge strengthened with NSM using CFRP plate. The railroad bridge is usually under vibration and impact in service state. Therefore, it is important that the effective strengthening performance must be exhibited under the service loading is acted. To widely apply the NSM method for the concrete railroad bridge in field, it needs that reasonable strengthening parameter such as strengthening ratio has to be investigated and evaluated when the strengthening design is conducted. In this study, to suggest more reasonable strengthening ratio, material and geometrical uncertainty was considered and applied by Monte Carlo Simulation (MSC) technique. Lastly, the critical strengthening ratio of concrete railroad bridge strengthened with NSM using CFRP plate was evaluated by using the limit state function with the target reliability index.

• Korean Journal of Materials Research
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• v.20 no.1
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• pp.19-24
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• 2010

The current study examined Ag migration from the Ag paste bump in the SABiT technology-applied PCB. A series of experiments were performed to measure the existence/non-existence of Ag in the insulating prepreg region. The average grain size of Ag paste was 30 nm according to X-ray diffraction (XRD) measurement. Conventional XRD showed limitations in finding a small amount of Ag in the prepreg region. The surface morphology and cross section view in the Cu line-Ag paste bump-Cu line structure were observed using a field emission scanning electron microscope (FE-SEM). The amount of Ag as a function of distance from the edge of Ag paste bump was obtained by FE-SEM with energy dispersive spectroscopy (EDS). We used an electron probe micro analyzer (EPMA) to improve the detecting resolution of Ag content and achieved the Ag distribution function as a function of the distance from the edge of the Ag paste bump. The same method with EPMA was applied for Cu filled via instead of Ag paste bump. We compared the distribution function of Ag and Cu, obtained from EPMA, and concluded that there was no considerable Ag migration effect for the SABiT technology-applied printed circuit board (PCB).

• Journal of Conservation Science
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• v.34 no.3
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• pp.195-209
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• 2018

In this study, the characteristics of various raw hairs used for traditional Korean brushes were examined; further, the characteristics and deterioration patterns of Korean, Chinese, and Japanese brushes were compared, with a quantitative evaluation to assess the brush performance. The tensile strength was generally found to be higher with a greater fiber thickness. Among the hairs examined, the back and flank hair of goat was more damaged than that in other parts, and the tensile strength was low. Higher elasticity of the brush made with hair of high cysteine content was measured. Owing to deterioration by use of the brushes, artificial drying brushes had a higher yellowness index and lower tensile strength than natural drying brushes. Further, it was confirmed that brushes with good absorbency exhibited good consistency, but not good elasticity. Thus, the performance of the brush can be influenced by the kind of material used and the brush usage pattern. In addition, it is possible to identify the material science characteristics of brushes which have been produced only by experience; therefore, the results of this study could provide basic data for manufacturing brushes employed in conservation treatment, in the future.

• Applied Chemistry for Engineering
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• v.22 no.4
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• pp.395-399
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• 2011

Material of the gasket for lithium ion battery requires the chemical resistance, the electrical insulting property, the compression set, the anti-contamination level and the low temperature resistance. We compounded ethylene propylene diene monomer (EPDM), which showed widely different solubility parameter index, with adjusting the amount of metal oxide as an activator. We did long-term test and compression set against an electrolyte with consideration for operating conditions in lithium-ion battery. In these tests, we checked the physical, chemical characteristics and the effect to lithium ion battery with different kinds of activators. In case of rubber with ZnO as an activator, through 1000 h depositing test in propylene carbonate which is one of representative solvents, we could get the satisfying characteristics and result. However, $Zn^{2+}$ had eluted in the ion elution test. So, ZnO should be limited in EPDM compound for the gasket material in lithium-ion battery.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.317-325
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• 2020

The development of a technique that can monitor the cracks, which is one of the typical types of damage, is necessary to secure the structural safety of elastically restrained cantilever-type beams with a tip mass that is used widely in infrastructure. Impedance techniques have been actively researched to detect cracks, and the cracks were estimated mainly by experimentally investigating the relationship between the crack and impedance signal. This study examined the correlation between the change in the impedance signals due to the crack, and the natural frequency obtained analytically. After updating the analysis model for the intact beam, the impedance signal was measured while gradually inflicting cracks in the cantilever-type beam, and the damage index was obtained. The results were compared with the natural frequencies calculated from the updated analysis model to investigate the correlation. A close correlation was observed between the experimentally obtained impedance damage index, and the analytically calculated natural frequency. Using this correlation, the structural characteristics could be evaluated more accurately from the damage estimation results, and the behavior of the structure could be predicted effectively using the analysis model.

• Korean Journal of Construction Engineering and Management
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• v.13 no.2
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• pp.58-69
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• 2012

In modern society, rooftops and underground spaces are utilized for overcoming a confined space limitation of metropolitan areas. Therefore, floor covering construction is also increasing steadily. From the user's viewpoint, skid resistance performance of floor covering methods is a very important performance criterion for safety and amenity, but an appropriate design and assessment criteria for skid resistance performance are not available. This study presents the skid resistance performance assessment method of floor covering methods considering the sidewalk skid resistance standard of Seoul city and the guideline of the Ministry of Land, Transport and Maritime Affairs(MLTM) of Korea for road safety facilities'installation and maintenance. For this research, three alternatives among urethane floor covering methods are selected and their skid resistance performance is analyzed through an experimental study. The analyzed performance is also evaluated by the skid resistance performance assessment method. Finally, the comprehensive performance assessment including the results of skid resistance performance assessment is conducted by Value Analysis(VA) in order to encourage the construction methods of floor covering which have a high skid resistance performance. As a result of VA, the particle method which the skid resistance performance is improved up to four times more than other alternatives shows the highest performance index of 83.86.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.180-180
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• 2011

하천의 정상적인 기능 및 상태를 유지하기 위하여 필요한 최소유량을 의미하는 하천유지유량은 하천수질보전, 하천생태계보호, 하천경관보전, 염수침입 방지, 하구막힘 방지, 하천시설물 및 취수원보호, 지하수위 유지 등을 감안하여 산정하게 된다. 하천유량 변화는 하천내 동 식물에 영향을 미치며, 특히 고등 생물인 어류의 서식처, 산란장소 및 산란조건 등은 유량 및 수위변화에 민감하게 반응하므로 하천구간별 어류의 서식처 유지에 적절한 수심, 유속 등 수리 조건을 제공할 수 있는 유량을 산정하게 된다. 국내에서는 90년대 후반부터 생태계를 고려한 하천유지유량 개념이 도입되었으며, 어류의 적절한 수생 서식환경 평가를 위해 주로 유량 점증 방법론(IFIM, Instream Flow Incremental Methodology) 개념에 입각한 물리서식처 모형을 이용한 연구가 진행되어 왔다. 본 연구에서는 낙동강수계 13개 지점을 선정하여 어류상 조사를 실시하여 어류의 물리서식처 모형과 수심-유속-유량 관계곡선을 이용한 간단법을 이용하여 생태계 보전을 위한 필요유량을 산정하였다. 어류 물리서식처 모형으로는 어류서식환경 평가에 가장 광범위하게 이용되고, 생태적 특성을 반영할 수 있는 유량점증방법론의 PHABSIM(Physical HABitat SIMulation) 모형을 선택하였다. 현장 모니터링 및 문헌조사를 통해 각 지점별 대표어종을 선정하고, 유량, 수심, 저수로 하천단면, 하상재료와 같은 수리특성을 조사하고, 선정된 한계단면에 대한 유량측정을 실시하였으며, 수심-유속-유량 관계곡선을 통하여 각 지점의 대표어종이 서식할 수 있는 최소유량을 산정하였다. 또한 지점별로 서식처 적합도 지수(HSI, Habitat Suitability Index)와 가중가용면적(WUA, Weighted Usable Area)를 산정하였으며, 이는 PHABSIM 모형의 적용에 이용되었다. 물리서식처 모형과 간단법 적용결과를 비교해본 결과, 모든 지점에서 물리서식처 모형 적용결과가 간단법에 비해 크게 산정되었는데, 이는 간단법이 성어기 서식에 필요한 최소 수리조건을 선택하였지만, PHABSIM의 경우 성어기 어류서식의 최적 수심 및 유속을 이용하여 가중가용면적을 산정하기 때문인 것으로 판단된다. 어류서식과 관련된 많은 관련 데이터가 축적된다면 어류서식처에 맞는 최적의 생태유량을 보다 정확하게 산정할 수 있을 것으로 판단된다.

• Composites Research
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• v.22 no.5
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• pp.1-7
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• 2009

The vehicle structure of Automated People Mover(APM) made of aluminum honeycomb sandwich with WR580INF4000 glass-fabric epoxy laminate facesheets was evaluated by structural test and finite element analysis. The test of the vehicle structure was conducted according to JIS E 7105. The structural integrity of vehicle structure was evaluated by stress, deflection and natural frequency obtained from dial-gauge and acceleration sensor. And the proposed finite element models were compared with the results of structural test. The results of finite element analysis showed good agreement with those of structural test. Also, in order to improve the stiffness of vehicle structure, the modified underframe model with reinforced side sill was proposed in design stage. The composite vehicle structures with modified underframe model had the improved structural stiffness about 44%.