• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.06a
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• pp.677-678
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• 2007

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.11
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• pp.26-34
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• 2006

The thermo-mechanical analysis and test were performed for plate structure under mechanical and thermal loading conditions. Infrared heating system and hydraulic loading system were used to simulate mechanical and thermal environment for the plate structure which is similar to the fin of the airframe. Also, FEM analysis using plastic option was added to evaluate thermo-mechanical behavior. Thermo-mechanical tests were conducted at elevated temperature and rapid heating(10℃/sec) condition with external loading together. To investigate the effect of heating environment, the strength at room temperature was compared with that of elevated temperature and rapid heating condition. A methodology for test and analysis for supersonic vehicle subjected to aerodynamic loading and heating was generated through the study. These experimental and analysis results can be used for designing thermal resistance structures of the supersonic vehicle.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.6
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• pp.1063-1072
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• 2000

Kinetic tests on pyrolysis of the mixture of waste automobile lubricating oil and polystyrene were carried out with thermogravimetric technique at the heating rates of 0.5, 1.0, $2.0^{\circ}C/min$ in a stirred batch reactor. The activation energy and the reaction order were determined at conversions of 1 to 100% using differential method. The mixture of waste automobile lubricating oil and polystyrene was pyrolyzed at lower temperature rather than waste automobile lubricating oil and polystyrene. respectively. Also, the thermal decomposition took place in two broad reaction steps. The pyrolyzed oil of mixture represented high selectivity of styrene monomer and dimer like that of polystyrene pyrolyzed products.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.98-98
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• 2009

용접에 의해 발생하는 용접잔류응력은 강구조물의 피로성능, 파괴양상 등에 영향을 주고 있으나 이러한 용접잔류응력을 예측하는 것은 쉽지 않다. 이러한 용접잔류응력을 예측하는 방법으로는 열탄소성해석과 같은 수치적 방법과 실험적 방법이 있다. 열탄소성해석의 경우 실제문제를 이상화하는 과정에서 매우 복잡한 모델링 기술이 필요하다. 또한, 측정방법에서는 표면의 잔류응력을 측정할 수 있는 홀드링법과 X-선법 등이 있고, 내부 잔류응력의 측정방법으로는 중성자회절법이 있다. 그러나 홀드링법의 경우, 사용범위의 한계와, 중성자회절법에서의 내부 잔류응력을 측정할 수 있는 두께의 제약이 있어 후판의 잔류응력을 측정하는 것은 한계가 있다. 따라서 본 연구에서는 용접잔류응력의 생성근원인 고유변형도를 측정하고 이것으로부터 맞대기용접에서 발생하는 두께방향의 용접잔류응력을 계측하였다.

• Composites Research
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• v.31 no.6
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• pp.371-378
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• 2018

In this study, the thermoelastic properties of poly lactic acid (PLA) based nanocomposites are predicted by molecular dynamics (MD) simulation and a micromechanics model. The stereocomplex mixed with L-lactic acid (PLLA) and D-lactic acid (PDLA) is modeled as matrix phase and a single walled carbon nanotube is embedded as reinforcement. The glass transition temperature, elastic moduli and thermal expansion coefficients of pure matrix and nanocomposites unit cells are predicted though ensemble simulations according to the hydrolysis. In micromechanics model, the double inclusion (D-I) model with a perfect interface condition is adopted to predict the properties of nanocomposites at the same composition. It is found that the stereocomplex nanocomposites show prominent improvement in thermal stability and interfacial adsorption regardless of the hydrolysis. Moreover, it is confirmed from the comparison of MD simulation results with those from the D-I model that the interface between CNT and the stereocomplex matrix is slightly weak in nature.

• Computational Structural Engineering
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• v.9 no.1
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• pp.65-76
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• 1996

The initiation and growth of microcracks or microvoids inside concrete results in the progressive degradation of concrete. This damage processing along processing along with plastic deformation is main cause of nonlinear behavior of concrete. In this study, a continuum damage model of concrete is developed for the analysis of the nonlinear behavior of concrete due to damage and elasto-plastic deformation. Anisotropic damage tensor is used to describe the anisotropy of concrete and hypothesis of equivalent elastic energy is used to define the effective elastic tensor. The damage model including the damage evolution law and constitutive equation is derived with damage variable and damage surface which is defined by damage energy release rate by using the Helmholtz free energy and dissipation potential based on the thermodynamic principles. By adopting a typical plasticity model of concrete, plasticity of concrete is included to this model. Afinite element analysis program implemented with this model was developed and finite element analysis was performed for the analyses of concrete subjected to uniaxial and biaxial loadings. Comparison of the results of analysis with those of experiments and other models shows that the model successfully predicts the nonlinear behavior of concrete.

• Polymer Science and Technology
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• v.21 no.2
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• pp.149-156
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• 2010

전기방사 탄소섬유와 s-VGCFs는 그 미세구조의 특성 때문에 응용분야가 서로 다르다. 전기방사 탄소나노섬유는 유기물을 섬유화하고 그것을 탄화하기 때문에 VGCFs에 비해서 낮은 가격에 대량생산이 가능하고 촉매를 사용하지 않기 때문에 전극으로 사용할 경우 금속불순물에 대한 부반응의 우려가 없다. 한편, 결정성이 낮고 세공이 잘 발달되어 비표면적이 크기 때문에 이온을 흡착해서 에너지를 저장하는 전기화학 캐패시터나 가스 흡착 분리나 촉매의 지지체로 사용하는데 장점이 있다. 이에 비해서 s-VFCFs는 섬유의 직경이 기존의 VGCF에 비해서 작으면서 잘 발달된 흑연구조가 동심원 구조를 하고 있어 굴곡강도가 크고 열 및 전기전도도가 우수하여 납축전지나 Li 이온전지의 충전제로 사용하여 역학적 특성과 향상시켜 주는 역할을 한다. 또한, 금속과 복합화하여 가벼우면서도 강도를 증가시켜주는 보강재로 사용가능하다.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.369-376
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• 1998

원자로 압력용기는 원자력발전소의 일차 압력경계를 구성하는 핵심 부품으로 이의 건전성은 원전의 안전성과 수명관리에 결정적인 영향을 미친다. 탄소강으로 구성된 압력용기는 노심에 근접하게 위치하여 운전중 계속되는 고속중성자 조사로 인하여 인성이 감소한다. 운전중 비상노심 냉각수가 주입되어 압력용기가 급격하게 냉각되면서 압력이 높게 유지되거나 재가압이 되는 가압열충격 현상이 발생하는 경우 조사취화된 압력용기가 적절한 안전여유를 가지지 못할 수도 있다. USNRC에서는 이에 대한 종합적인 연구결과를 바탕으로 가압열충격 규정을 제정하여 가압열충격 기준온도(RT$_{PTS}$)의 계산 방법과 심사기준온도를 제시하였다. 가압열충격 심사기준온도의 결정근거가 기술되어 있는 SECY 82-465에 의하면 축방향 용접부에 대한 위험도를 평가하여 270℉를 심사기준온도로 정하고 원주방향 용접부에 대해서는 30℉를 더하여 300℉를 심사기준온도로 제시하였다. 이 연구에서는 이렇게 제정된 원주방향 용접부에 대한 심사기준온도의 적정성을 평가하기 위하여 균열방향에 따른 가압열충격 위험도를 VISA-II 코드로 평가하였다. 우선 가압열충격 기준온도 제정 시 사용된 방법과 결과들을 검토하고 NRC의 계산결과를 재현하였다. 이를 바탕으로 원주방향 용접부에 대한 위험도를 평가한 결과 균열방향의 차이를 고려하기 위해 적용된 기술적 여유도인 30℉는 과도한 보수성을 내포하고 있음을 알 수 있었다. 원주방향 용접부가 축방향 용접부와 동일한 수준의 가압열충격 위험도를 가지기 위한 심사기준온도 차이는 50℉ 이상인 것으로 평가되었다.을 수 있었다.ngineering because this field has large uncertainties on predicting the effect of earthquake on structures. This paper is based on the presented paper at the Bertero Symposium held in January 31an4 February 1 at Berkeley, California, USA which was entitled "Needs to Evaluate Real Seismic Performance of Buildings-Lessons from 1995 Hyogoken-Nambu Earthquake-". The lessons for buildings from the damage due to the Hyogoken-Nambu Earthquake are necessity to develop more rational seismic design codes based upon a performance-based design concept, and to evaluate seismic performance of existing buildings. In my keynote lecture at the Korean Association for Computational Structural Engineering, the history of seismic design and use of structural analysis in Japan, the lessons for buildings from

• Journal of the Korean Society of Hazard Mitigation
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• v.1 no.1 s.1
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• pp.127-138
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• 2001

Although Carbon/Carbon Composites(CFRCs) have excellent mechanical properties at high temperature, the disadvantage of combustion in air restricts their applications. Thus a lot of investments have been studied to improve the drawback of CFRCs. In this study, SiC used as a thermal protective coating material possesses almost the same expansion coefficient compared to that of carbon, so SiC was coated on 4D (directional) CFRCs by Pack-Cementation process. For the 4D CFRCs coated with SiC, optical microscopy observations were performed to estimate the coating mechanism involved and TGA tests were also performed to evaluate the improvement of combustion resistance. And their high temperature combustion properties were investigated by the arc torch plasma test. From the results, it is found that the mechanical properties and high temperature combustion properties of the 4D(directional) CFRCs coated with SiC were much better than bare 4D CFRCs.

• Korean Journal of Materials Research
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• v.3 no.4
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• pp.372-380
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• 1993

In order to improve the oxidative resistance of carbon/carbon composites, aluminium-isopropoxide and aluminium-tri-sec-butoxide sol were coated on the surface of 2D--carbon/carbon composiles and the effects uf coating were investigated. The effects of oxidative resistance were dominant in the case of catalyst/alkoxide mole ratio, 0.07, and $H_2O$/alkoxide mole ratio, 100. Through the dynamic TGA analysis with the heating rate of 20%/min, oxidative initiation tempera~ ture was enhanced about $80^{\circ}C$. The oxidative resistance effects of alkoxide sol were improved according to the times of coating. Also the 20% weight loss time of coated samples by TGA analysis was 20% better than that of un~ coated samples. The thickness of 1^{st} coated layer was about 3${\mu}$m and that of $2^{nd}$ and $3^{nd}$ coated layers was about respectively 4~5${\mu}$m and the weight loss were increased with the increasing of thermal shock test times.