• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.9
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• pp.279-287
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• 2018

Sealants are an important element of modern architecture and serve as a building protection against weathering by providing barriers against ingress of moisture, air, and other materials. Exposure to a variety of environments often reduces lifespan due to changes in physical, chemical and mechanical characteristics, and UV, humidity, and temperature expansion are important issues that are directly related to durability. In this study, a combined deterioration test chamber was developed to simulate the environment of the open air as an instrument for verifying the durability of structural sealing materials indoors. In order to replicate special weather conditions, such as yellow dust, acid rain, and contamination by microorganisms, it was deemed impossible to replicate the outdoor environment by 100 %, and the results of the results of the results of the external exposure test of the structural sealant and the combined deterioration testing device. As a result of the displacement test of the outdoor exposure test, it was determined that the sealant was breaking apart and that it would be smooth, and the displacement would be up to three times greater than the initial material value of 1 year. The displacement test results of the combined deterioration test device show the tendency to deteriorate, decreasing the elasticity and tensile characteristics. In the case of denatured silicon, the current 400 cycles have been completed to confirm 12 months of degradation of the external exposure. The deformation of the test specimen cannot be verified with the naked eye, so it is considered that the conditions of the specimen are more stable than the silicon sealant. As a result of the outdoor exposure test, if the combined deterioration test device is structured and proposed in the relevant guidance or specification, the anticipated lifespan of 12 months in the actual use environment can be verified indoors and below 3 months later, economically.

• Composites Research
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• v.17 no.1
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• pp.18-28
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• 2004

In order to evaluate the strength of carbody structures of railway rolling stock made of laminated fiber-reinforced composite materials, total laminate approach was introduced. Structural analyses were conducted to check the basic design of hybrid composite carbody structures of the Korean Tilting Train eXpress(TTX) with the service speed of 180km/h. The mechanical tests were also conducted to obtain strengths of composite laminates. The results show that all stress components of composite carbody structures are inside of failure envelopes and total laminate approach is recommended to predict the failure of hybrid composite carbody structures at the stage of the basic design.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.47.2-47.2
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• 2009

인체의 뼈와 같은 손상된 경조직을 치료 또는 대체하기위한 정형외과용 임플란트를 설계하는데 있어 뼈의 생체역학적 특성과 유사한 성질을 갖는 다공성 지지체에 대한 연구가 최근 관심을 끌고 있다. 다공성 지지체는 조직이 원활히 재생될 수 있어야 하며, 또한 주변 조직과도 생물학적인 고착이 잘 되도록 기공들이 상호 연결된 구조를 가져야 한다. 이와 같은 다공성 지지체용 소재를 제조하기 위하여 본 연구에서는 타이타늄 분말을 사용하여 3차원 적층조형공정으로 다공성 타이타늄 지지체를 제조하였다. 제조된 다공체의 물성 및 기계적 특성을 평가하기 위하여 압축시험과 변형해석을 수행하였으며, 아울러 제조된 지지체의 생체적합성 향상을 위하여 양극산화 공정 등의 표면처리를 수행하여 그에 대한 특성을 평가하였다. 분말야금 공정으로 제조된 지지체는 골조직의 성장에 적합한 약 $300\sim400{\mu}m$의 기공 크기를 갖도록 제어하였고, 기공도는 60~75%로 제어하였다. 아울러 다공성 타이타늄의 생체적합성을 부여하기 위하여 양극산화공정으로 지지체의 표면에 Ca 및 P을 포함하는 산화층을 형성시키는 표면처리를 수행하였다. 양극산화공정에 의하여 표면에 미세기공을 포함하는 산화층을 형성시킬 수 있었으나 이와 같은 표면구조는 조골세포의 부착과 영향에는 큰 영향을 미치지 않는 것으로 확인되었다.

• Journal of Conservation Science
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• v.33 no.6
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• pp.467-483
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• 2017

In this study, the degradation properties by temperature stress of $Araldite^{(R)}$ rapid-curing epoxy resin used for inorganic cultural heritages, was identified. The tensile and tensile shear strength of durability decreased for 12,624 hours at temperatures of $40{\sim}60^{\circ}C$. In terms of stability of external stress and temperature, the slow-curing epoxy was superior to the rapid-curing epoxy, and cultural heritage conservation plans should therefore consider the strength and stress properties of restoration materials. Color differences increased for 12,624 hours at temperatures of $40{\sim}60^{\circ}C$, and glossiness decreased. Both color and gloss stability were weak, which necessitates the improvement of optical properties. Thermal properties (weight loss, decomposition temperature, and glass transition temperature) of adhesives are linked to mechanical properties. Interfacial properties of the adherend and water vapor transmission rates of adhesives are linked to performance variation. For porous media (ceramics, brick, and stone), isothermal and isohumid environments are important. For outdoor artifacts on display in museums, changes in physical properties by exposure to varying environmental conditions need to be minimized. These results can be used as baseline data in the study of the degradation velocity and lifetime prediction of rapid-curing epoxy resin for the restoration of cultural heritages.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.939-941
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• 2017

The use of composites is increasing for lightweight aerospace structures. Among these structures, the ring frame and the parts of the projectile body are mainly made of a fiber reinforced composite material which is less susceptible such as delamination to structural damage. As the use of fiber reinforced composites increases, interest in modeling efficient methods of stiffness and strength is increasing. This paper predict the mechanical strength according to the repeating unit cell(RUC) of the 2-D triaxial braided composites of fiber reinforced composites. Yarn slice definition, incremental approach and stiffness reduction model were used as strength prediction. Finally, the results of strength prediction are verified by comparing with experimental data of 2-D triaxial braided composites specimens.

• Tunnel and Underground Space
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• v.22 no.2
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• pp.77-85
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• 2012

In a material, micro-cracks can be progressively occurred, propagated and finally lead to failure when it is subjected to cyclic or periodic loading less than its ultimate strength. This phenomenon, fatigue, is usually considered in a metal, alloy and structures under repeated loading conditions. In underground structures, a static creep behavior rather than a dynamic fatigue behavior is mostly considered. However, when compressed air is stored in a rock cavern, an inner pressure is periodically changed due to repeated in- and-out process of compressed air. Therefore mechanical properties of surrounding rock mass and an inner lining system under cyclic loading/unloading conditions should be investigated. In this study, considering an underground lined rock cavern for compressed air energy storage (CAES), the mechanical properties of a lining system, that is, concrete lining and plug under periodic loading/unloading conditions were characterized through cyclic bending tests and shear tests. From these tests, the stability of the plug was evaluated and the S-N line of the concrete lining was obtained.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 1999.04a
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• pp.44-44
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• 1999

전적으로 해외기술에 의존하고 있는 소프트 닙 캘린더 피복의 국산화를 위해 시험 제작 된 소프트 닙 캘린더용 연질롤의 캘린더링 효과를 구명하기 위해서 공정 변수에 따른 신문 용지의 물성변화를 평가하였다. 연질 롤로는 (주)광성고무롤에서 시험제작된 경도 90 Shore D의 것을 사용하였으며, 캘린 더링 시의 압력, 가열 롤의 표면온도, 닙 체류 시간, 유입지의 함수율 변화에 따른 신문용지 의 별크, 평활도, 광택도, 인장강도, 인열강도, 불투명도 변화를 조사하였다. 별크는 캘린더링 시 압력, 가열 롤의 표면온도, 닙 체류시간의 증가에 따라 감소하였다. 가열 롤의 표면온도가 높을수록 별크가 크게 감소되었으며, 닙 체류시간이 짧은 경우에는 1 120 226;C 이하에서 캘린더링을 실시하는 것이 별크 유지에 효과적이었다. 평활도는 가열 롤의 표연 온도, 닙 체류시간이 증가함에 따라 개선되었으며, 선압과 함 수율 증가에 의해서도 상승되는 경향을 보였. 인장강도는 유입지의 함수율, 닙 체류시간, 가열 롤의 표면온도가 모두 상승할 경우 증 가하는 결과를 나타내었다. 이는 함수율 증가에 의해 섬유의 유연성이 향상된 상태에서는 칼렌더링 온도와 닙체류 시간 증가에 의한 섬유의 기계적 변형과 열전달에 의한 섬유의 열 변형이 효과적으로 발생하여 섬유간 결합면적이 증가된 결과로 생각되었다. 인열강도는 소프트닙 캘린더링 후 전반적으로 감소하였으나 캘린더링 온도와 닙체류시 간은 인열강도에 미치는 영향은 적은 것으로 나타났다. 소프트 닙 캘린더링 시 발생하는 인 열강도의 저하를 막기 위해서는 닙 체류시간을 짧게 적용하고 섬유의 열변형이 종이의 표변 에서만 일어날 수 있도록 유입지 함수율과 가열롤의 표면온도를 적절히 조절하는 것이 필요 하리라 판단되었다.광택도는 온도와 압력이 증가할수록 증가하였으나, 닙 체류시간에 따라서는 큰 변화를 나타내지 않았으며 120도씨에서는 닙 체류시간의 증가에 따라 광택도가 오히려 감소하기도 하였다. 불투명도는 벌크와 마찬가지로 압력이 높고 가열롤의 표면온도가 높은 경우 낮게 나타 났다 특히 닙 체류시간의 증가에 따라 감소하는 경향을 보였다.보였다.

• Elastomers and Composites
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• v.49 no.1
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• pp.24-30
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• 2014

3-Amino-1,2,4-triazole (ATA) (2.5 and 5.0 phr) was incorporated into a immiscible maleated ethylene propylene diene rubber(mEPDM)/maleated high density polyethylene(mHDPE) (50 wt%/50 wt%) blend by melt mixing. Effects of the ATA on structure, mechanical and rheological properties of the blend was investigated. FT-IR and DMA results revealed that supramolecular hydrogen bonding interactions between the polymer chains occur by reaction of ATA with maleic anhydride grafted onto the component polymers in the blend, which induces the physical crosslinks in the blend. FE-SEM analysis showed that mEPDM forms a dispersed phase in continuous mHDPE matrix, and the blend with the ATA has finer phase morphology as compared to the blend without the ATA. By the addition of ATA in the blend, there were significant increases in tensile strength, modulus and elongation-at-break as well as elastic recoverability. Melt rheology studies revealed that ATA induced substantial increase in storage modulus and complex viscosity of the blend at the melt state.

• Applied Chemistry for Engineering
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• v.26 no.5
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• pp.615-620
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• 2015

Polypropylene (PP)/bamboo fiber (BF) composites were fabricated by twin screw extruder in order to investigate effects of the compatibilizer on physical properties of PP/BF composites. The content of BF changed from 10 to 25 wt% and that of the compatibilizer was fixed at 3 wt%. Maleic anhydride grafted PP (PP-g-MAH) was used to increase the compatibility between PP and BF as a compatibilizer. Chemical structures of the composites were confirmed by the existence of carbonyl group (C=O) stretching peak at $1,700cm^{-1}$ in FT-IR spectrum. Considering the degradation and mechanical properties, the optimum extrusion conditions were selected to be $210^{\circ}C$ and 100 rpm, respectively. There was no distinct changes in melting temperature of the composites, but the crystallization temperature increased by $10-20^{\circ}C$ owing to the heterogeneous nuclei of BF. It was checked that the optimum BF content was in the range of 15-20 wt% from the results of tensile and flexural properties of the composites. The effect of the compatibilizer on mechanical properties was confirmed by SEM images of fractured surface and contact angles.

• Clean Technology
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• v.20 no.3
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• pp.205-211
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• 2014

Biomass-based plastics containing the biomass content higher than 25 wt% have been considered as environment-friendly materials due to their effects on the reduction in the $CO_2$ emission and petroleum consumption as well as biodegradability after use. This article described the effect of the additions of oxo-biodegradable additive, 4 kinds of plant biomass, unsaturated fatty acid, citric acid in the properties of polyethylene films. Bio films were prepared using a variety of biomasses and tested for feasibility as a food packaging film. Mechanical properties such as tensile strength and percent elongation at break were evaluated. Husk biomasses from such as corn, soybean, rice, and wheat were pulverized using air classifying mill (ACM) and four different types of packaging films with thickness of $50{\mu}m$ were prepared using the pulverized biomass and low density polyethylene/linear low density polyethylene. The packaging film with wheat husk biomass was found to have greater mechanical properties of elongation and tensile strength than the other samples. Biodegradability of bio film was measured to be 51.5% compared to cellulose.