• Nuclear Engineering and Technology
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• 제51권7호
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• pp.1816-1821
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• 2019

This research investigates the feasibility of using the thermoelectric power to monitor the thermal embrittlement in 2507 super duplex stainless steel (SDSS) exposed to a temperature between $280^{\circ}C$ and $500^{\circ}C$. It is well known that the precipitation of Cr-rich ${\alpha}^{\prime}$ phase as a result of the spinodal decomposition is the major cause of the embrittlement and the loss of corrosion resistance in this material. The specimens are thermally aged at $475^{\circ}C$ for different holding times. A series of mechanical testing including the tensile test, Vickers microhardness measurement, and Charpy impact test are conducted to determine the property changes with holding time due to the embrittlement. The mechanical strengths and ferrite hardness exhibit very similar trends. Scanning electron microscopy images of impactfractured surfaces reveal a ductile to brittle transition in the fracture mode as direct evidence of the embrittlement. It is shown that the thermoelectric power is highly sensitive to the thermal embrittlement and has an excellent linear correlation with the ferrite hardness. This paper, therefore, demonstrates that the thermoelectric power is an excellent nondestructive evaluation technique for detecting and evaluating the $475^{\circ}C$ embrittlement of field 2507 SDSS structures.

• 한국환경과학회지
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• 제30권6호
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• pp.429-439
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• 2021

Food waste is both an industrial and residential source of pollution, and there has been a great need for food waste reduction. As a preliminary step in this study, waste reduction is quantitatively modeled. This study presents two models based on kinetics: a simple kinetic model and a mass transport-shrinking model. In the simple kinetic model, the smaller is the reaction rate constant ratio k₁, the lower the rate of conversion from the raw material to intermediate products. Accordingly, the total elapsed reaction time becomes shorter. In the mass transport-shrinking model, the smaller is the microbial decomposition resistance versus the liquid mass transfer resistance, the greater is the reduction rate of the radius of spherical waste particles. Results showed that the computed reduction of waste mass in the second model agreed reasonably with that obtained from a few experimantal trials of biodegradation, in which the microbial effect appeared to dominate. All calculations were performed using MATLAB 2020 on PC.

• Elastomers and Composites
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• 제57권1호
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• pp.13-19
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• 2022

Polycarbonate diol-based waterborne polyurethane (WPU) was prepared by prepolymer mixing process. The prepolymer mixture contained the polycarbonate diol, isophorone diisocyanate (IPDI), dimethylol propionic acid, triethylamine, and ethylenediamine (EDA). The NCO/OH ratio in the prepolymer was adjusted by controlling the molar ratio of IPDI, and its effects on the properties of WPU were studied. The structure of WPU was characterized by fourier transform infrared spectroscopy. The average particle size increased and viscosity decreased with increasing NCO/OH ratio and EDA content in WPU. The reduced phase separation between soft and hard segments increased glass transition temperature. The reduction in the thermal decomposition temperature could be attributed to the low bond energy of urethane and urea groups, which constituted the hard segment. Additionally, the polyurethane chain mobility was restricted, elongation decreased, and tensile strength increased. The hydrogen bond between the hard segments formed a dense structure that hindered water absorption.

• Nuclear Engineering and Technology
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• 제53권4호
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• pp.1331-1344
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• 2021

This study is to evaluate the seismic capacity of the fire-damaged cabinet facility in a nuclear power plant (NPP). A prototype of an electrical cabinet is modeled using OpenSees for the numerical simulation. To capture the nonlinear behavior of the cabinet, the constitutive law of the material model under the fire environment is considered. The experimental record from the impact hammer test is extracted trough the frequency-domain decomposition (FDD) method, which is used to verify the effectiveness of the numerical model through modal assurance criteria (MAC). Assuming different temperatures, the nonlinear time history analysis is conducted using a set of fifty earthquakes and the seismic outputs are investigated by the fragility analysis. To get a threshold of intensity measure, the Monte Carlo Simulation (MCS) is adopted for uncertainty reduction purposes. Finally, a capacity estimation model has been proposed through the investigation, which will be helpful for the engineer or NPP operator to evaluate the fire-damaged cabinet strength under seismic excitation. This capacity model is presented in terms of the High Confidence of Low Probability of Failure (HCLPF) point. The results are validated by the proper judgment and can be used to analyze the influences of fire on the electrical cabinet.

• 한국포장학회지
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• 제28권2호
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• pp.89-95
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• 2022

The goal of this study was to evaluate the effect of spent coffee grounds (SCG) biofiller on the morphological, thermal, mechanical and hydrolytic degradation characteristics of poly(lactic acid) (PLA) based biocomposites. The PLA-based biocomposite films were fabricated by using a high-viscosity kneading and hot-pressing machine. The PLA/SCG biocomposites were analyzed with SEM, DSC, TGA, UTM and hydrolytic degradation test. Aggregation in the PLA matrix is a result of increasing SCG concentrations. In the thermal properties, it was described that the cold crystallization temperature (T_cc) decreased as SCG was added to PLA. When SCG was incorporated to PLA, the degradation onset temperature (T_onset) revealed a diminish. The elastic modulus increased while tensile strength of PLA diminished as SCG was applied. Through hydrolysis analysis, the decomposition of PLA was accelerated with the addition of SCG. This research confirmed the possibility of devloping an eco-friendly packaging material with high degradability as SCG hasten the breakdown of PLA.

• Structural Engineering and Mechanics
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• 제86권1호
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• pp.69-83
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• 2023

Analytical solutions to problems are crucial because they provide high-quality comparison data for assessing the accuracy of numerical solutions. Benchmark analytical solutions for the vibrations of cracked functionally graded material (FGM) plates are not available in the literature because of the high level of complexity of such solutions. On the basis of first-order shear deformation plate theory (FSDT), this study proposes analytical series solutions for the vibrations of FGM rectangular plates with side or internal cracks parallel to an edge of the plates by using Fourier cosine series and the domain decomposition technique. The distributions of FGM properties along the thickness direction are assumed to follow a simple power law. The proposed analytical series solutions are validated by performing comprehensive convergence studies on the vibration frequencies of cracked square plates with various crack lengths and under various boundary condition combinations and by performing comparisons with published results based on various plate theories and the theory of three-dimensional elasticity. The results reveal that the proposed solutions are in excellent agreement with literature results obtained using the Ritz method on the basis of FSDT. The paper also presents tabulations of the first six nondimensional frequencies of cracked rectangular Al/Al2O3 FGM plates with various aspect ratios, thickness-to-width ratios, crack lengths, and FGM power law indices under six boundary condition combinations, the tabulated frequencies can serve as benchmark data for assessing the accuracy of numerical approaches based on FSDT.

• 한국습지학회지
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• 제17권3호
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• pp.283-292
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• 2015

토양으로부터 방출되는 $CO_2$의 양은 전 지구적 지구 탄소 순환에서 가장 큰 방출 중 하나로 알려져 있다. 특히 토양 내 미생물의 유기물질 분해 과정에 의해 방출되는 이산화탄소의 양은 토양의 탄소 저장량을 장기적으로 결정하는 요인이 되므로 그 양을 정량화 하는 것이 필요하다. 본 연구는 토양에서 고라니의 분변이 $CO_2$ 배출에 미치는 영향을 파악하기 위해 수행하였다. 그리고 고라니의 분변이 토양의 $CO_2$ 배출에 주는 영향과 토지의 이용에 따라 변화하는 $CO_2$ flux를 정량화 하였다. 그 결과 고라니 분변 내 많은 유기물질은 토양 미생물의 활성화에 영향을 주고 그로 인해 토양의 호흡 및 토양 내 물리 화학적인 변화가 발생되어 토양의 유기물 함량이 서로 다르게 나타남을 확인할 수 있었다. 특히 4개 지역의 토양(경작지, 휴경지, 버드나무 군락, 갈대습지)의 C/N ratio와 $CO_2$ flux는 분변의 유무와 통계적으로 매우 유의미한 상관 관계를 나타냈으며(P<0.01), 분변의 영향을 받은 토양의 $CO_2$ flux는 분변의 영향을 받지 않은 토양보다 2-20배 더 높은 것으로 나타났다. 이 연구는 고라니의 분변이 토양에 주는 영향과 야생동물 분변을 이용한 토양 물질 순환 연구를 통해 육상 생태계 및 토양권의 물질 순환과 그 영향의 정도를 정량화 하였다는 점에서 큰 의의가 있는 연구이다.

• 한국건설순환자원학회논문집
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• 제6권4호
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• pp.95-102
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• 2012

고층건축물의 구조부재로 적용되는 철골이나 고강도콘크리트로 시공된 경우 내화대책은 필수 불가결한 요소이며 특히, 고강도콘크리트로 적용된 경우 폭렬 등에 의한 단면결손이 발생하기 쉽기 때문에 이에 대한 대책이 필요하다. 즉, 내화성능 확보를 위해 온도상승을 허용범위 이내로 억제하는 대책이 필요하며 이 중 가장 효율적인 방법이 내화성 마감을 실시하는 것이다. 일반적으로 내화성 마감재에 사용되는 시멘트계 재료는 C-S-H, 및 CH가 단계적으로 열 분해되어 압축강도는 저하하게 된다. 내화성능을 발휘하기 위해 고온에서 강도감소가 작고 안정적인 고온특성을 보인다면 보다 효과적으로 성능 발현이 가능할 것이다. 본 연구는 고층건축물의 철골 및 콘크리트 부재의 효과적인 내화성능 발현을 위한 경량 내화성 마감재 개발을 위한 연구로 내화성능이 우수하다고 알려진 Alumino-silicate계 재료를 내화성 마감에 적용하기 위해 고온특성에 대해 검토하였다. 검토 결과, 플라이애시, 메타카올린 및 경량골재를 활용한 경량 내화성 마감재는 고온에서 비교적 안정적인 특성을 발현하여 내화성 마감재로의 효용성을 확인할 수 있었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.412-412
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• 2009

Carbon-based nano materials have a significant effect on various fields such as physics, chemistry and material science. Therefore carbon nano materials have been investigated by many scientists and engineers. Especially, since graphene, 2-dimemsonal carbon nanostructure, was experimentally discovered graphene has been tremendously attracted by both theoretical and experimental groups due to their extraordinary electrical, chemical and mechanical properties. Electrical conductivity of graphene is about ten times to that of silicon-based material and independent of temperature. At the same time silicon-based semiconductors encountered to limitation in size reduction, graphene is a strong candidate substituting for silicon-based semiconductor. But there are many limitations on fabricating large-scale graphene sheets (GS) without any defect and controlling chirality of edges. Many scientists applied micromechanical cleavage method from graphite and a SiC decomposition method to the fabrication of GS. However these methods are on the basic stage and have many drawbacks. Thereupon, our group fabricated GS through Thermo-electrical Pulse Induced Evaporation (TPIE) motivated by arc-discharge and field ion microscopy. This method is based on interaction of electrical pulse evaporation and thermal evaporation and is useful to produce not only graphene but also various carbon-based nanostructures with feeble pulse and at low temperature. On fabricating GS procedure, we could recognize distinguishable conditions (electrical pulse, temperature, etc.) to form a variety of carbon nanostructures. In this presentation, we will show the structural properties of OS by synthesized TPIE. Transmission Electron Microscopy (TEM) and Optical Microscopy (OM) observations were performed to view structural characteristics such as crystallinity. Moreover, we confirmed number of layers of GS by Atomic Force Microscopy (AFM) and Raman spectroscopy. Also, we used a probe station, in order to measure the electrical properties such as sheet resistance, resistivity, mobility of OS. We believe our method (TPIE) is a powerful bottom-up approach to synthesize and modify carbon-based nanostructures.

• 한국재료학회지
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• 제26권12호
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• pp.733-740
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• 2016

$Al_2O_3$ nanosol dispersed under ethanol or N-Methyl-2-pyrrolidone(NMP) was studied and optimized with various dispersion factors and by utilizing the silane modification method. The two kinds of $Al_2O_3$ powders used were prepared by thermal decomposition method from aluminum ammonium sulfate$(AlNH_4(SO_4)_2)$ while controlling the calcination temperature. $Al_2O_3$ sol was prepared under ethanol solvent by using a batch-type bead mill. The dispersion properties of the $Al_2O_3$ sol have a close relationship to the dispersion factors such as the pH, the amount of acid additive(nitric acid, acetic acid), the milling time, and the size and combination of zirconia beads. Especially, $Al_2O_3$ sol added 4 wt% acetic acid was found to maintain the dispersion stability while its solid concentration increased to 15 wt%, this stability maintenance was the result of the electrostatic and steric repulsion of acetic acid molecules adsorbed on the surface of the $Al_2O_3$ particles. In order to observe the dispersion property of $Al_2O_3$ sol under NMP solvent, $Al_2O_3$ sol dispersed under ethanol solvent was modified and solvent-exchanged with N-Phenyl-(3-aminopropyl)trimethoxy silane(APTMS) through a binary solvent system. Characterization of the $Al_2O_3$ powder and the nanosol was observed by XRD, SEM, ICP, FT-IR, TGA, Particles size analysis, etc.