• 대한화장품학회지
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• 제44권1호
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• pp.23-29
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• 2018

본 연구에서는 생체재료인 콜라겐과 합성 단량체인 아크릴아마이드를 연속가교 하여, 하이드로젤 기반의 콜라겐 겔을 제조하였다. 아크릴아마이드의 함량 및 가교 정도에 따라, 1.5 kPa에서 3.0 kPa까지 다양한 강도(E)를 갖는 콜라겐 겔을 제조할 수 있었다. 또한, 콜라겐 겔에 다공성 기공을 도입하고 진피세포를 내부에 담지하여, 겔 강도에 따른 세포 성장 및 거동을 확인하였다. 상대적으로 강도가 높은 겔에서 세포의 성장은 느렸지만 GAG 합성 및 분비는 활성화되는 것을 확인하였다. 콜라겐 겔의 기계적 물성에 따라 세포의 성장 및 활성이 영향을 받는 것을 알 수 있었으며, 이는 향후 인공피부 제조 및 응용, 나아가 다양한 조직공학 분야의 기반 기술로 활용 가능하리라 기대된다.

• 한국결정성장학회지
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• 제26권3호
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• pp.126-130
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• 2016

Ti-합금은 낮은 밀도, 낮은 탄성계수, 우수한 고온강도, 내산화성 및 인체적합성으로 자동차와 항공산업 및 바이오 산업에서 구조용 재료로 널리 연구되고 있다. 본 연구에서는 Ti-합금 중 대표적인 조성인 Ti-64(6 wt% Al, 4 wt% V) 합금에 대한 결정학적 특성과 미세조직에 대해서 알아보고자 하였다. XRD 분석을 통하여 Ti-64 샘플의 주요 결정상을 분석하였고, FE-SEM 및 EDX 분석을 통하여 Ti-64 합금 샘플의 미세구조를 화학조성의 차이에 의해 고찰하였다.

• Advances in aircraft and spacecraft science
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• 제8권4호
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• pp.345-372
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• 2021

The analysis of nonlinear vibrations, buckling, post-buckling, flutter boundary determination and post-flutter behavior of a homogeneous curved plate assuming cylindrical bending is conducted in this article. Other assumptions include simply-supported boundary conditions, supersonic aerodynamic flow at the top of the plate, constant pressure conditions below the plate, non-viscous flow model (using first- and third-order piston theory), nonlinear structural model with large deformations, and application of mechanical and thermal loads on the curved plate. The analysis is performed with constant environmental indicators (flow density, heat, Reynolds number and Mach number). The material properties (i.e., coefficient of thermal expansion and modulus of elasticity) are temperature-dependent. The equations are derived using the principle of virtual displacement. Furthermore, based on the definitions of virtual work, the potential and kinetic energy of the final relations in the integral form, and the governing nonlinear differential equations are obtained after fractional integration. This problem is solved using two approaches. The frequency analysis and flutter are studied in the first approach by transferring the handle of ordinary differential equations to the state space, calculating the system Jacobin matrix and analyzing the eigenvalue to determine the instability conditions. The second approach discusses the nonlinear frequency analysis and nonlinear flutter using the semi-analytical solution of governing differential equations based on the weighted residual method. The partial differential equations are converted to ordinary differential equations, after which they are solved based on the Runge-Kutta fourth- and fifth-order methods. The comparison between the results of frequency and flutter analysis of curved plate is linearly and nonlinearly performed for the first time. The results show that the plate curvature has a profound impact on the instability boundary of the plate under supersonic aerodynamic loading. The flutter boundary decreases with growing thermal load and increases with growing curvature.

• 전기화학회지
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• 제17권1호
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• pp.65-70
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• 2014

본 실험에서는 다양한 조성의 AMPS, POEM 및 GMA를 함유하는 공중합체를 합성하고, AMPS의 술폰산기와 $Li_2CO_3$와의 산염기 반응 및 에폭시기의 가교반응을 유도하여 가교결합된 poly(POEM-co-AMPSLi-co-GMA) 전해질을 제조하였다. POEM의 결정융점은 AMPS 및 POEM의 몰분율에 따라 변화되는 특징을 관찰할 수 있었으며, 리튬이온이 도입된 이후 대체적으로 감소되는 경향이 나타났다. 가교된 고분자의 이온전도도는 GMA의 함량이 증가할수록 다소 감소되는 결과가 나타났지만, 16 mol%까지는 $1.0{\times}10^{-6}S\;cm^{-1}$ 이상의 값을 보여주었다. 특히, 자기-도핑형 전해질임에도 불구하고 2 mol%에서 최대 $4.08{\times}10^{-6}S\;cm^{-1}$의 높은 상온이온전도도가 얻어졌으며, 상온에서 6 V까지 우수한 전기화학적 안정성을 보여주었다. 또한 가교된 고분자전해질은 필름성형이 가능하며, 0.11 MPa의 탄성계수 및 270%의 변형율을 보여주었다.

• 한국도로학회논문집
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• 제3권3호
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• pp.135-146
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• 2001

기존의 교면포장공법의 근본적인 문제점으로 인해 새로운 교면포장 공법이 점차 부각되고 있는 실정이며, 새로운 교면포장 공법으로 연구되고 있는 것이 라텍스 개질 콘크리트를 이용하는 것이다. 따라서, 본 연구에서는 신설 콘크리트 교량 교면포장으로 덧씌우기된 LMC의 강도발현 특성과 덧씌우기 될 때의 기존콘크리트와의 부착특성을 파악하고자 하였다. 이런 연구를 위해 라텍스 혼입률에 따른 라텍스 개질 콘크리트의 압축강도와 휨강도, 그리고 기존콘크리트와의 부착강도를 측정하였다. 본 연구결과 라텍스 혼입량 증가로 폴리머 입자들의 볼베어링 작용, 연행된 공기 및 라텍스 안에 있는 계면활성제의 분산작용에 의하여 LMC의 작업성과 휨강도를 증가시킨다는 사실을 파악 할 수 있었고, LMC와 기존 콘크리트 슬래브와의 부착강도는 크게 증진함을 알 수 있었다.

• Smart Structures and Systems
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• 제4권2호
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• pp.209-220
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• 2008

A methodology for the seismic vulnerability assessment of historical monuments is presented in this paper. The ongoing work has been conducted in Tunisia within the framework of the FP6 European Union project (WIND-CHIME) on the use of appropriate modern seismic protective systems in the conservation of Mediterranean historical buildings in earthquake-prone areas. The case study is the five-century-old Zaouia of Sidi Kassem Djilizi, located downtown Tunis, the capital of Tunisia. Ambient vibration tests were conducted on the case study using a number of force-balance accelerometers placed at selected locations. The Enhanced Frequency Domain Decomposition (EFDD) technique was applied to extract the dynamic characteristics of the monument. A 3-D finite element model was developed and updated to obtain reasonable correlation between experimental and numerical modal properties. The set of parameters selected for the updating consists of the modulus of elasticity in each wall element of the finite element model. Seismic vulnerability assessment of the case study was carried out via three-dimensional time-history dynamic analyses of the structure. Dynamic stresses were computed and damage was evaluated according to a masonry specific plane failure criterion. Statistics on the occurrence, location and type of failure provide a general view for the probable damage level and mode. Results indicate a high vulnerability that confirms the need for intervention and retrofit.

• 한국재료학회지
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• 제23권7호
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• pp.353-358
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• 2013

To improve coating ability and the life of the coating, Ti based composite materials with hydroxyapatite(HA) should be developed. The raw materials of Ti-26wt%, Nb-1wt%, and Si with 10wt% HA were mixed for 24 h by a mixing machine and milled for 1 h to 6 h by planetary mechanical ball milling. Ti-26%Nb-1%Si-(10%HA) composites, composed of nontoxic elements, were fabricated successfully by spark plasma sintering(SPS) at $1000^{\circ}C$ under 70MPa. The relative density of the sintered Ti-Nb-Si-HA composites using the 24 h mixed powder, and the 6 h milled powder, was 91% and 97 %, respectively. The effects of HA contents and milling time on microstructure and mechanical properties were investigated by SEM and hardness tester, respectively. The Vickers hardness of the composites increased with increasing milling time and higher HA content. The Young's modulus of the sintered Ti-26%Nb-1%Si-10%HA composite using the 6 h-milled powder was 55.6 GPa, as obtained by compression test. Corrosion resistance of the Ti-26wt%Nb-1wt%Si composite was increased by milling and by the addition of 10wt%HA. Wear resistance was improved with increasing milling time. Biocompatibility of the Ti-Nb-Si alloys was improved by the addition of HA.

• 한국재료학회지
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• 제30권1호
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• pp.38-43
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• 2020

Sand casting 3D printing uses a binder jetting method to produce a mold having complicated shape by spraying a binder on sand coated with activator. Appropriate heat treatment process in sand mold fabrication can increase the degree of polymerization to improve flexural strength. However, long heat treatment of over 24 hours decreases flexural strength and reliability due to chemical bond decomposition through thermal degradation. The main role of the activator is to control the reaction rate between the polymer chains. As a result, when the activator composition is increased from 0.15 wt% to 0.25 wt%, the flexural strength is increased by 218 N/㎠. However, excess activator (0.40 wt%) has been shown to decrease reliability without increasing flexural strength. The main role of the binder is to control the flexural strength of the specimen. As the binder composition is increased from 2.00 wt% to 4.00 wt%, the flexural strength increases to about 255 N/㎠, indicating the maximum flexural strength increase. Finally, the reliability of the flexural strength of the fabricated specimens is evaluated by a Weibull plot. Weibull modulus calculations are used to evaluate the flexural strength reliability of the specimens, and maximum reliability value of 11.7 is obtained at 0.20 wt% activator composition. Therefore, it is confirmed that this composition has maximum flexural strength reliability.

• 한국건축시공학회지
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• 제13권4호
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• pp.351-359
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• 2013

고로슬래그는 콘크리트의 적용시 효율적인 가치향상과 관련하는 많은 장점도 있으나, 고로슬래그의 사용량 증대에 따른 부작용도 나타나고 있다. 따라서 고로슬래그 미분말의 활용성 증대를 위해 High Volume Slag를 자극제 종류별, 치환율별, 조강제 혼입율별, NaOH, $Na_2SiO_3$ 혼합사용시, 폐알칼리자극제 혼입율별 특성을 알아보기 위해 실험하였다. 실험결과, 압축강도의 경우 수산화나트륨을 제외한 모든 알칼리자극제에서 치환율이 증가함에 따라 강도가 증진되었다. 알칼리자극제 중 규산나트륨이 동탄성계수와 흡수율 등에서 높게 나타났으며, 조강제의 경우 혼입율 1.5%와 고로슬래그 치환율 75%가 높은 강도증진을 나타내었다. 폐알칼리 자극제의 경우 모든 실험에서 각기 다른 결과를 나타내었다.

• 대한조선학회논문집
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• 제58권1호
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• pp.17-23
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• 2021

The membrane-type Liquefied Natural Gas (LNG) cargo tank is equipped with a double barrier to seal the LNG, of which the secondary barrier serves to prevent LNG leakage and mainly uses fiber-reinforced composite materials. However, the composite materials have thermal expansion anisotropy, which deteriorates shape distortion and mechanical performance due to repeated thermal loads caused by temperature changes between cryogenic and ambient during the unloading of LNG. Therefore, in this study, the longitudinal thermal expansion characteristics of the composite materials were obtained using a vertical thermo-mechanical analyzer, and the elastic modulus was obtained through the tensile test for each temperature to perform thermal load analysis for each direction. This is considered that it is useful to secure reliability from the viewpoint of the design of materials for a LNG cargo hold.