• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1993년도 봄 학술발표회논문집
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• pp.125-133
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• 1993

Preflex composit girder is intended for a better use on both steel and concrete by introducting prestress into the lower flange concrete with preflection. In Korea, recently preflex bridges are widely used especially for urban construction but the design method depends on the conventional ASD(Allowable Stress Design). This paper suggests an optimization model for the design of preflex composite bridges based on LIFD(Load Resistance Factor Design). The optimization algorithm adopted for the NLP model proposed in the paper is the FTM(Flexible Tolerance Method) which is very efficient for the approximate continuous optimization. For the discrete optimum results, a pesudo discrete optimization is used for the economical round-up to the available dimensions. The economic effectiveness of optimum design based on the LRFD method is investigation by comparing the results with those of the ASD method. Based on applications to the actual design examples, it may be concluded that the optimization model suggested in the paper provides economical but reliable design. And the suggested in the paper provides economical but reliable design. And the computer code for the automatic optimum design of preflex bridges developed in the paper for a CAD system may be successfully used in practice.

• 대한기계학회논문집A
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• 제29권11호
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• pp.1480-1487
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• 2005

Metal matrix composites(MMCs) have been rapidly becoming one of the strongest candidates for structural materials fur many high temperature application. However, among the various high temperature environments in which metal matrix composites was applied, thermal shock is known to cause significant degradation in most MMC system. Due to the appreciable difference in coefficient of thermal expansion(CTE) between reinforcement and metal matrix, internal stresses are generated following temperature changes. Infernal stresses affect degradation of mechanical properties of MMC by causing microscopic damage in interface and matrix during thermal cycling. Therefore, the nondestructive evaluation on thermal shock damage behavior of SiC/A16061 composite has been carried out using ultrasonics. For this study, SiC fiber reinforced metal matrix composite specimens fabricated by a squeeze casting technique were thermally cycled in the temperature range 298$\~$673 K up to 1000cyc1es. Three point bending test was conducted to investigate the efffct of thermal shock damage on mechanical properties. The relationship between thermal shock damage behavior and the propagation characteristics of surface wave and SH-ultrasonic wave was discussed by considering the result of SEM observation of fracture surface.

• 한국추진공학회지
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• 제10권2호
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• pp.115-128
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• 2006

스크램제트 추진기술에 대한 최근 개발동향과 주요기술을 분석하였다. 스크램제트엔진은 지난 10여년간 급속한 기술 발전으로 지상시험에서 비행시험 단계에 접어들고 있으며, 수년 내 실용시험을 목표로 활발하게 연구개발 중이다. 광범위한 비행 마하수를 만족하는 이중연소램제트와 이중모드램제트 형태의 엔진은 각각 군용과 민수용으로 개발되고 있으며, 복합엔진은 차세대 우주발사체의 대안으로 개발되고 있다. 엔진 작동 특성의 미케니즘에 대한 정확한 이해와 이에 상응되는 기술, 흡열연료 및 CSiC 복합재료를 사용한 내열 문제 해결, 가변 흡입구와 노즐을 이용한 안정된 추진력 구현을 목전에 두고 있다.

• 조명전기설비학회논문지
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• 제26권3호
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• pp.9-15
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• 2012

In this paper, we deal with a surface discharge that caused an aggravation of the dielectric strength in the $N_2/O_2$ mixture gas, When composit dielectrics were formed from the use of a solid dielectric. It was found from this study that the surface discharge voltage was deeply involved in the mixture ratio of $O_2$, the electrical property of the solid dielectric, kind of the solid dielectric, an electric field at the triple junction and a medium effect. These results expect basic data that will be used to transmission and distribution power system equipment using the $N_2/O_2$ mixture gas.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2017년도 춘계학술대회
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• pp.793-796
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• 2017

영상신호는 신호를 처리하는 과정에서 다양한 잡음에 의해 훼손되어지며, 이러한 신호를 복원하기 위한 많은 연구가 이루어지고 있다. 영상에 첨가되는 잡음에는 salt and pepper 잡음, AWGN(additive white Gaussian noise) 및 두 잡음이 혼합된 복합잡음이 대표적이다. 따라서 본 논문에서는 복합잡음 환경에서 훼손된 영상을 복원하기 위해, 잡음 판단을 통해 국부 마스크의 중심화소가 salt and pepper 잡음인 경우, 2차원 스플라인 보간법 및 메디안 필터로 처리하고, AWGN인 경우, 화소변화에 따른 가중치 필터로 처리하는 알고리즘을 제안하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제31권4호
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• pp.401-409
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• 2007

Because of the various excellent characteristics of cast basalt materials. such as, anti-corrosion, anti-wearing, good hardness. high chemical stability, of which steel may not possess, the steel-basalt composite pipes are used in severe environments for compensating the defects of steel. However. without sufficient mechanical investigation prior to application. the basalt liners in steel-basalt composite pipes may be cracked and broken or the basalt liners are omitted from steel pipes in applications. In these cases, the merits of basalt materials may disappear and the basalt liners may not play their good roles as expected. Therefore, it is required that mechanical behavior of steel-basalt composite pipes and surrounding environments be fully examined before installation. The limit of bending moment with which steel-basalt composite pipe may safely endure is calculated and the limit curvature of the composite pipe in the safe range is presented in this paper. The temperature distributions and the thermal stresses are also computed and the limit difference of temperatures between inner and outer side of composite pipe is given together.

• 한국재료학회지
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• 제25권1호
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• pp.48-53
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• 2015

$TiH_2$ nanopowder was made by high energy ball milling. The milled $TiH_2$ and CNT powders were then simultaneously synthesized and consolidated using pulsed current activated sintering (PCAS) within one minute under an applied pressure of 80 MPa. The milling did not induce any reaction between the constituent powders. Meanwhile, PCAS of the $TiH_2$-CNT mixture produced a Ti-TiC composite according to the reaction ($0.92TiH_2+0.08CNT{\rightarrow}0.84Ti+0.08TiC+0.92H_2$, $0.84TiH_2+0.16CNT{\rightarrow}0.68Ti+0.16TiC+0.84H_2$). Highly dense nanocrystalline Ti-TiC composites with a relative density of up to 99.7% were obtained. The hardness and fracture toughness of the dense Ti-8 mole% TiC and Ti-16 mole% TiC produced by PCAS were also investigated. The hardness of the Ti-8 mole% TiC and Ti-16 mole% TiC composites was higher than that of Ti. The hardness value of the Ti-16 mole% TiC composite was higher than that of the Ti-8 mole% TiC composite without a decrease in fracture toughness.

• 한국막학회:학술대회논문집
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• 한국막학회 1997년도 춘계 총회 및 학술발표회
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• pp.13-16
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• 1997

The permeation, solution and diffusion of simple gases ($He, H_2, O_2, N_2$ and CH$_4$) and condensible vapers($CO_2, SO_2, C_2H_4$ and $C_3H_8$), and the mixed gases ($O_2/N_2$ mixtures and $CO_2/CH_4$ mixtures) through composite membrane was studied. Composit membranes were made by deposition of aromatic fluorocarbons onto polymer substrams of porous Celgard in a microwave discharge. In the both cases of simple gases and condensible vapors, as the kinetic molecular diameter of the permeant molecules increased, the permeability decreased. However, when the kinetic molecular dimemr are similar, the condensible vapors showed higher permeabilities than that of permanent gases. The vapor solubility increased with increasing critical temperature of the vapors. However, in the case of propane, despite its high critical temperature, it showed lower solubility than other vapors. The vapor diffusivity decreased with increasing kinetic diameter of the molecule. Compared to conventional polymers, the plasma polymers showed much lower values for vapor diffusivities. The pressure of the permeant did not affect the permeability. The permeability was also not affected by the composition in cases of mixed gases.

• 한국구조물진단유지관리공학회 논문집
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• 제14권2호
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• pp.153-160
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• 2010

다양한 요인에 의해 성능이 저하된 철근콘크리트 구조물은 보수 보강 공법이 요구된다. 현재 다양한 공법과 신소재를 이용한 보강법의 개발이 진행 중에 있다. 최근에 섬유보강 복합체(FRP)를 이용한 보강공법이 주목받고 있으며, 많은 연구와 개발이 진행 중에 있다. 본 논문에서는 FRP-알루미늄 유공복합보로 보강된 RC보의 화재거동에 관한 실험결과를 제시하고자 한다. 사전가력으로 손상시킨 RC보에 FRP-알루미늄 유공복합보로 보강후 화재노출시킨 결과, 손상율이 높아질수록 화재노출에 더욱 많은 영향을 받았으며, 보강효과가 떨어짐을 실험결과 나타났다.

• 한국안전학회지
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• 제23권6호
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• pp.131-137
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• 2008

SCP(Sand Compaction Pile) method that forms a composite ground by driving compacted sand piles into the soft ground. This method is one of the soil improvement techniques for reinforcing and strengthening soft ground deposits. This thesis describes the investigation on the behavior of soft ground reinforced with SCP by low improvement ratio. Direct shear test and consolidation test carried out to verified behavior of composite ground reinforced with SCP. Test results were discussed with reference to the amount of consolidation settlement, variation of shear resistance with area replacement ratio and effect of the stress concentration. And, laboratory model loading test carried out to verified the effect of the location and failure mode of reinforced embankment. Residual shear strength varies with the area replacement and constrict load in the low replacement ratio. Calculated stress concentration ratio overestimate than proposed valve by experimental, theoretical and analytical method. As regards the location, improving right below of the top of the slope was more effective than below of the toe of the slope. This thesis carried out to obtain fundamental information of behavior of the composit ground. Hereafter, centrifuge test that reproduce stress state of the in-situ must be necessary through the further study about pile penetration, reinforce position and construct time.