• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.2
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• pp.130-140
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• 2016

Floating floor is most commonly used at apartment houses in Korea for thermal insulation and reducing impact noise. But it in proven that the floating floor is not effective for reducing the floor impact noise in low frequency range. In most cases, impact sound pressure level under 63 Hz frequency band were actually increased by the resonance of resilient material, lightweight concrete and the finishing mortar installed on it. In this paper, an integrated floor system consist of 70 mm light weight concrete and 40 mm finishing mortar successively installed on the concrete slab was suggested to avoid the resonance. Integrated floor system increases total flexural stiffness and mass per unit area. The natural frequencies of first and second vibration mode were increased and acceleration response and floor impact sound level was decreased in all measurement range.

• Journal of Applied Reliability
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• v.15 no.4
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• pp.270-275
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• 2015

Purpose : UHMWPE (Ultra-high-molecular-weight-polyethylene) is one of the most widely used material in knife protection clothes because of high strength, elasticity, and light weight. The purpose of this study is to develop the accelerated life test method and predict the lifetime for the knife protection fabric composed by UHMWPE. Methods : In this study, degradation characteristics of UHMWPE fibers and knife protection fabric for cut resistance were evaluated under the hydrolysis and photo-degradation conditions. It was found out that the degradation rate of retained tensile strength was more significant in the photo-degradation than hydrolysis. Therefore, the failure time was determined as the time that the retained tensile strength in photo-degradation is less than 50%. Considering an acceleration factor for irradiance and exposure time, the lifetime was predicted from the calculated failure time. Results : As a result of the accelerated life test, the $B_{10}$ lifetime of knife protection fabric composed by UHMWPE fibers is estimated as 2.8 years for a 90% statistical confidence level. Conclusion: Since the lifetime is predicted by the view-point of radiant exposure in this study, there is a possibility that the estimated lifetime may differ from the actual lifetime. However, it is considered as an useful methodology to estimate the long-term lifetime of knife protection fabrics.

• International Journal of Concrete Structures and Materials
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• v.4 no.1
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• pp.3-8
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• 2010

This paper present the results of investigation on the use of rice husk ash as a partial substitute for cement in construction. One hundred and eighty specimens of concrete cubes were cast. 0, 5, 10, 15, and 20% partial replacement of cement with rice husk ash were carried at 1:2:4 mixes by weight with 0.60, 0.65, 0.70 water/cement ratio. The results indicated that compressive strengths of cubes at 0.6, water/cement were higher than 0.65 and 0.70. Also 5% partial replacement cement with rice husk ash at $28^{th}$ day average compressive strength value of $25.4\;N/mm^2$ compared well with 0% partial replacement of cement with rice husk ash of $26.28\;N/mm^2$. This shows that at 5% partial replacement of cement with rice husk ash can be used for structural concrete and at 15% replacement or more it can be used for non - structural construction works or light weight concrete construction. The cost analysis shows substantial amount of savings for the country.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.1
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• pp.132-138
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• 2016

Korea Aerospace Research Institute (KARI) is developing an electric-driven HALE UAV in order to secure system and operational technologies since 2010. Based on the flight tests and design experiences of the previously developed electric-driven UAVs, KARI has designed EAV-3, a solar-powered HALE UAV. EAV-3 weighs 53kg, the structure weight is 22kg, and features a flexible wing of 19.5m in span with the aspect ratio of 17.4. Designing the main wing and empennage of the EAV-3 the amount of the bending due to the flexible wing, 404mm at 1-G flight condition based on T-800 composite material, and side wind effects due to low cruise speed, $V_{cr}=6m/sec$, are carefully considered. Also, unlike the general aircraft there is no center of gravity shift during the flight because of the EAV-3 is the solar-electric driven UAV. Thus, static margin cuts down to 28.4% and center of gravity moves back to 31% of the Mean Aerodynamic Chord (MAC) comparing with the previously designed the EAV-2 and EAV-2H/2H+ to upgrade the flight performance of the EAV-3.

• Advances in materials Research
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• v.1 no.3
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• pp.221-231
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• 2012

In this study, the physical and mechanical properties of bamboo fiber reinforced epoxy composites were studied. Composites were fabricated using short bamboo fiber at four different fiber loading (0 wt%, 15 wt%, 30 wt% and 45 wt%). It has been observed that few properties increases significantly with respect to fiber loading, however properties like void fraction increases from 1.71% to 5.69% with the increase in fiber loading. Hence, in order to reduce the void fraction, improve hardness and other mechanical properties silicon carbide (SiC) filler is added in bamboo fiber reinforced epoxy composites at four different weight percentages (0 wt%, 5 wt%, 10 wt% and 15 wt%) by keeping fiber loading constant (45 wt%). The significant improvement of hardness (from 46 to 57 Hv) at 15 wt%SiC, tensile strength (from 10.48 to 13.44 MPa) at 10 wt% SiC, flexural strength (from 19.93 to 29.53 MPa) at 5 wt%SiC and reduction of void fraction (from 5.69 to 3.91%) at 5 wt%SiC is observed. The results of this study indicate that using particulate filled bamboo fiber reinforced epoxy composites could successfully develop a composite material in terms of high strength and rigidity for light weight applications compared to conventional bamboo composites. Finally, SEM studies were carried out to evaluate fibre/matrix interactions.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.436-437
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• 2006

Porcelain insulators have generally been used in Korea but polymer insulators which are superior in that they are light weight, explosion proof, impact proof, economical with construction characteristics, have been in use for the 154kV transmission line since 1999 following a worldwide trend towards the reduced weight, simplification and compact usage of new material insulators. However there have been approximately 500 cases of forest fires in Korea, so the transmission lines that for the most part pass through mountainous areas have been highly effected and the highly polymerized compound polymer insulator has raised concern about reliability in cases of exposure to forest fires. Therefore for the reliability assessment of the effect of forest fires on polymer insulators, mechanical and electrical characteristics are analyzed by an artificial flare test device and transmission facility surrounding conditions along with forest fire characteristics are surveyed. In addition to this, actual 90kV energized transmission line was tested with an artificial forest fire and the expanded usage of polymer insulators is presented through the analysis of mechanical and electrical characteristics and physical properties, and a study on the influence of forest fires on polymer insulators.

• Journal of Adhesion and Interface
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• v.7 no.4
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• pp.60-64
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• 2006

In modern vehicle construction the search for means of weight reduction, improving durability, increasing comfort and raising body stiffness are issues of priority to the design engineer. The intelligent usage of many materials such as high strength steel, light-alloys and plastics enables a significant vehicle weight reduction to be achieved. The classical joining techniques used in the automobile industry need to be newly-evaluated since they often do not present workable solutions for such mixed-material connections, for example aluminium/steel. Calculation/simulation methods have made progress as a key factor for broader and more cost-effective implementation of structural bonding. This will lead to reduction of spotwelds and accelerate the car development. A special focus of the paper is the use of high strength steel grades. It will be shown that adhesive bonding is a key tool for yielding the potential of advanced high strength steel for low gauging without compromising the stiffness. The latest status of adhesive development has been described. Improvements with physical strength and glass temperature as well as of process relevant properties are shown. Also the situation regarding occupational hygiene is treated, showing that by further spotweld point reduction the emission around the working area can be even lowered against the current praxis. High performing lightweight design cannot longer do without high performing crash durable adhesives.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.9 s.186
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• pp.61-67
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• 2006

Sandwich structures, which are composed of a thick core between two faces, are commonly used in many engineering applications because they combine high stiffness and strength with low weight. Accordingly, the usage of sandwich structure is very widely applied to the aircraft, the automobile and marine industry, etc., because of these advantages. In this paper, we have investigated the buckling protection of an inner structure plate and the useful corrugated configuration for contact, and the fabrication method of the inner structure plate for large area using the continuous molding process. Also, we have guaranteed the accuracy of the molding process through the micro corrugated mold fabrication and secured the accuracy and analyzed aspect properties of the inner structure plate fabricated for a large area using the partial mold process. We have compared molding simulation according to the aspect thickness of the corrugated configuration with the molding experiment results.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.7
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• pp.501-508
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• 2014

Floor finishing materials such as floor coverings and floor mats can reduce floor impact noise easily. When an impact was applied to the floor, its finishing material is deformed and the impact force that was applied to the concrete slab is changed. The softer finishing materials were, the more impact force decreased. An experimental study was performed using 14 PVC floor coverings and 16 floor mats to capture the characteristics of impact force and impact noise in the residential buildings. The test results show that the impact force spectrum and the floor impact noise spectrum have a linear relationship in the case of a bare concrete slab, and the characteristics of impact force reduction are the same as those of floor impact noise reduction.

• Journal of Welding and Joining
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• v.31 no.4
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• pp.1-6
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• 2013

Nowadays, the weight lightening of automotive is required as conserving the environment has become a major worldwide issue. To solve this issue, various researches for the use of light materials(Alalloy, Mgalloy)and ultra high strength steel as substitutes of the current structural material have been carried out. Application of laser stitch welding to the assembly of automotive produces improvement in strength, lightening of body, higher fuel efficiency, lower production cost as well as reduction in assemble line due to its fast welding speed, superior accessible and weld quality. This process overcomes the shortcomings of the current resistance spot welding such as high electricity consumption, electrode replacement, and economical, technical limitation in design and production method of automotives.