• 대한기계학회논문집
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• 제18권3호
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• pp.548-554
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• 1994

The high temperature fatigue crack growth behavior of SUS 304 stainless steel at $550^{\circ}C$ and $650^{\circ}C$ was investigated under various kinds of stress ratio and frequency in sinusoidal waveform on the basis of the non-linear fracture mechanics. The result arranging crack growth rate by modified J-integral J' showed influence of stress ratio and frequency. All the data obtained under the test at $550^{\circ}C$ were plotted within data band of da/dN-${\triangle}J_f$ relationship for cycle-dependent crack growth. On the basis of static creep and cycle-dependent data band; both time- and cycle-dependent crack growth behavior was observed under loading conditions at $650^{\circ}C$, but cycle-dependent crack growth behavior predominantly appeared and time-dependent crack growth behaviour was little observed under loading conditions at $550^{\circ}C$. Fractographic examinations for fracture surface indicated that the fracture mode was generally transgranular. The stripes were found on fracture surface and each stripe was accompanied by a crack tip blunting and an abrupt increase in the load-point displacement. The $J'_{an}$ had a validity in case of $650^{\circ}C, but scarcely had it in case of $550^{\circ}C$.

• 한국압력기기공학회 논문집
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• 제16권1호
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• pp.65-73
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• 2020

Integrity evaluations on a platen superheater were conducted as per ASME Section VIII Division 2(hereafter 'ASME VIII(2)') which was originally used for design with implicit consideration of creep effects. A platen superheater subjected to severe loading conditions of high pressure and high temperature at creep regime in a supercritical thermal plant in Korea was chosen for present study. Additional evaluations were conducted as per nuclear-grade high-temperature design rule of RCC-MRx that takes creep effects into account explicitly. Comparisons of the two results from ASME VIII(2) and RCC-MRx were conducted to quantify the conservatism of ASME VIII(2). From present analyses, it was shown that the design evaluation results exceeded allowable limits of RCC-MRx for the plant design conditions although limits of ASME VIII(2) were satisfied regardless of operation time, which means that design as per ASME VIII(2) might be potentially non-conservative in case of operation in creep range. A high-temperature design evaluation program as per RCC-MRx, called 'HITEP_RCC-MRx' has been used and it was shown that pressure boundary components can be designed reliably with the program especially for the loading conditions of long-term creep conditions.

• Composites Research
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• 제17권6호
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• pp.52-57
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• 2004

본 연구에서는 환경 챔버를 이용한 극저온 환경에서, 열.하중 사이클에 따른 탄소섬유강화 복합재의 인장 물성 변화를 고찰하였다. Graphite/epoxy 일방향 복합재 시편에 대하여 시편 상온파손하중의 절반을 가한 상태에서, 상온에서 $-50^{\circ}C$, $-100^{\circ}C$, 그리고 $-150^{\circ}C$ 까지 각각 3회, 6회, 그리고 10회의 열-하중 사이클을 수행한 후 복합재의 인장 강도와 강성을 측정하였다. 그 결과, 온도가 낮아질수록 복합재의 인장 강성은 증가한 반면, 인장 강도는 감소함을 보였다. 그러나 복합재의 인장 강성은 저온 사이클 횟수에 거의 영향을 받지 않았으며 인장 강도는 사이클을 수행하지 않았을 때 보다 오히려 저온 사이클 수행 후 증가함을 확인할 수 있었다. 따라서 실험결과의 고찰을 위해 저온에서 복합재 시편의 열팽창계수를 측정하였고, 주사 전자 현미경 사진을 통해 섬유와 모재의 계면을 분석하였다.

• Advances in concrete construction
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• 제9권4호
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• pp.355-365
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• 2020

The influence of temperature on the material of concrete filled columns (CFCs) under axial loading has been quantitatively studied in this research. CFCs have many various advantages and disadvantages. One of the important inefficiency of classic CFCs design is the practical lack of hooped compression under the operational loads because of the fewer variables of Poisson's rate of concrete compared to steel. This is the reason why the holder tends to break away from the concrete core in elastic stage. It is also suggested to produce concrete filled steel tube columns with an initial compressed concrete core to surpass their design. Elevated temperatures have essentially reduced the strengths of steel tubes and the final capacity of CFCs exposed to fire. Thus, the computation of bearing capacity of concrete filled steel tube columns is studied here. Sometimes, the structures of concrete could be exposed to the high temperatures during altered times, accordingly, outcomes have shown a decrement in compressive-strength, then an increase with the reduction of this content. In addition, the moisture content at the minimal strength is declined with temperature rising. According to Finite Element (FE), the column performance assessment is carried out according to the axial load carrying capacities and the improvement of ductility and strength because of limitations. Self-stress could significantly develop the ultimate stiffness and capacity of concrete columns. In addition, the design equations for the ultimate capacity of concrete columns have been offered and the predictions satisfactorily agree with the numerical results. The proposed based model (FE model of PEC column) 65% aligns with the concrete exposed to high temperature. Therefore, computed solutions have represented a better perception of structural and thermal responses of CFC in fire.

• Elastomers and Composites
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• 제46권3호
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• pp.223-230
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• 2011

본 연구에서는 자원 재활용 측면에서 매트릭스수지로 재활용플라스틱과 보강재로 친환경 천연섬유로 구성된 그린복합재료를 제조하고 그 특성을 탐구하였다. 먼저 재활용폴리에틸렌과 천연섬유인 목분을 이용하여 이축 압출공 정 방법으로 목분함량이 서로 다른 펠렛을 제조하였다. 이 펠렛을 사용하여 압축성형 방법으로 목분/재활용폴리에틸렌 그린복합재료를 제조하고, 그들의 굴곡특성, 인장특성, 충격특성, 열변형온도 그리고 파단거동에 미치는 목분함량의 영향을 조사하였다. 결과는 목분/재활용폴리에틸렌 그린복합재료의 굴곡강도, 굴곡탄성률, 인장탄성률 및 열변형온도 는 목분함량이 증가함에 따라 크게 향상된 반면, 인장강도와 충격특성은 감소한다는 나타내었다. 주사전자현미경으로 관찰한 파단거동은 재활용폴리에틸렌의 유연한 파단현상과 비교하여 목분함량이 증가함에 따라 변화하는 충격거동 경향을 정성적으로 뒷받침해주었다.

• Computers and Concrete
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• 제22권2호
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• pp.209-220
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• 2018

In order to evaluate the effect of hybrid fibers on the flexural performance of tunnel segment at room temperature, twelve reinforced self-consolidating concrete (SCC) symmetric inclination beams containing steel fiber, macro polypropylene fiber, micro polypropylene fiber, and their hybridizations were studied under combined loading of flexure and axial compression. The results indicate that the addition of mono steel fiber and hybrid fibers can enhance the ultimate bearing capacity and cracking behavior of tested beams. These improvements can be further enhanced along with increasing the content of steel fiber and macro PP fiber, but reduced with the increase of the reinforcement ratio of beams. The hybrid effect of steel fiber and macro PP fiber was the most obvious. However, the addition of micro PP fibers led to a degradation to the flexural performance of reinforced beams at room temperature. Meanwhile, the hybrid use of steel fiber and micro polypropylene fiber didn't present an obvious improvement to SCC beams. Compared to micro polypropylene fiber, the macro polypropylene fiber plays a more prominent role on affecting the structural behavior of SCC beams. A calculation method for ultimate bearing capacity of flexural SCC symmetric inclination beams at room temperature by taking appropriate effect of hybrid fibers into consideration was proposed. The prediction results using the proposed model are compared with the experimental data in this study and other literature. The results indicate that the proposed model can estimate the ultimate bearing capacity of SCC symmetric inclination beams containing hybrid fibers subjected to combined action of flexure and axial compression at room temperature.

• 한국구조물진단유지관리공학회 논문집
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• 제27권5호
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• pp.75-83
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• 2023

프리스트레스트 콘크리트 철도 교량에서 발생하는 과다한 솟음 문제를 분석하는 연구의 일환으로, 이 논문에서는 콘크리트 구조물의 시간에 따른 솟음 증가량을 나타내는 크리프 계수에 대하여 산정 방법과 분석 결과를 제시한다. 설계기준의 크리프 계수 산정식을 사용하여 국내 12개 지역의 기후 조건(상대습도와 온도)을 적용한 크리프 계수를 구하고, 기후 조건에 대한 지역별 및 재하 시기별 차이가 크리프 계수에 미치는 영향을 분석한다. 재하 초기에 많이 발생하는 크리프를 적절하게 산정하기 위하여 시기별 기후조건을 구분하여 고려하도록 시간 단계해석 방법을 적용하여 상세 분석한다. 지역의 평균 기후조건을 적용하여 구한 크리프 계수는 시간 단계 해석으로 구한 크리프 계수의 평균과 비슷하며, 시간 단계 해석을 통하여 크리프 계수에 미치는 상대습도와 온도의 상쇄, 중첩 효과 및 재하 초기 기후 효과를 적절하게 나타낼 수 있음을 보인다.

• 대한환경공학회지
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• 제35권1호
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• pp.31-37
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• 2013

기존 흡착제들보다 우수한 흡착성능을 확보하고, 특히 특정한 용제에 대한 흡착성능을 극대화하기 위하여 $1,100m^2/g$의 비표면적을 갖는 활성탄소섬유를 기본흡착제로 적용하였고, 여기에 활성금속을 첨착시켜 흡착성능과 선택성을 제고하고자 하였다. 활성금속은 screening 연구를 수행하여 최종적으로 Cu, Cr을 선정하였으며, 활성금속첨착 활성탄소섬유의 제조변수는 제조온도, 제조시간, 활성금속의 종류이었다. 물성측정 및 흡착반응실험을 통하여 금속을 $100^{\circ}C$에서 5시간 동안 첨착하였을 경우 acetone gas 흡착성능이 가장 높게 나타났으며, 기존 활성탄소섬유보다 2배 이상의 높은 흡착성능을 확인하였다. 한편, 활성금속첨착 활성탄소섬유의 확산 및 흡착에 필요한 최소 접촉시간은 최소한 0.5초 이상은 유지해야 함을 확인할 수 있었다.

• 설비공학논문집
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• 제17권6호
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• pp.505-513
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• 2005

We measured the time-dependent concentration of VOCs emitted from Ondol floor, furniture, and the wall made of various building materials. After obtaining results from the previous measurement, we developed the estimation equations of the concentration decay, and obtained the estimated graphs for the concentration decay under different air change rates and loading factor conditions by using the estimated equations. We conducted our tests by applying our measurements to real residences for 110 days in the case of furniture and for 40 days in the case of the floor. We also conducted experiments in the cases of various wall materials for 7 days which totaled 10 times. We used the GC/FID for experiments for real residences accord-ing to the specified procedures of the NIOSH 1501, and carried out experiments for wall materials according to the specified procedures of the ASTM 5116-97. When conducting experiments for wall materials, we set the temperature and relative humidity at $23^{\circ}C$ and $50\%$, respectively. We also set the air change rate and loading factor at 0.7/h and $1.617 m^2/m^3$, respectively. Our results showed that it is possible to predict proplrly the time-dependent concentration decay of VOCs by using logarithmic functions in both cases of experiments for real residences and for wall materials. Furthermore, we found that the concentration decay rate of VOCs increased rapidly as the air exchange rate increased while the concentration decay rate decreased as the loading factor increased.

• 한국입자에어로졸학회지
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• 제6권4호
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• pp.173-183
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• 2010

The high temperature pleated filter bags which were used during this study were made of pleated nonwoven fabric of heat and acid resistant polysulfonate fibers which can withstand the heat up to $300^{\circ}C$ and have a filtration area which is 3 to 5 times larger than the conventional round filter bags. Cartridge module packed with 3 kind of the sulfur impregnated activated-carbon based sorbents were inserted in the inner of the pleated filter bag. This type of pleated filter bag was designed to remove not only the particulate matter but also the gaseous elemental mercury. The electrostatic precipitator part can enhance the particulate removal efficiency and reduce the pressure drop of the pleated filter bag by agglomerated particles to form a more porous dust layer on the surface of the pleated bag which is increased the filter bag cleaning efficiency. In addition, the most of particles are separated from the flue gas stream through the cyclone and the electrostatic precipitator part which were installed at the lower part and main body part of the convergence particulate collector, respectively. Thus reduce particulate loading of the high temperature pleated filter bags were applied in this study to analyze the removal characteristics of particulate matter and gaseous elemental mercury.