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철도차량 내장재용 발열 복합재 라미네이트 패널 작동 내구성 평가
박주엽,강동훈 한국비파괴검사학회 2023 한국비파괴검사학회지 Vol.43 No.1
최근 코로나 바이러스(COVID –19) 대유행으로 인해 호흡기 질환에 대한 위험성 및 예방의 중요성이크게 증가하였다. 특히, 대중교통 환경의 경우 삼밀(밀집, 밀접, 밀폐)환경으로 호흡기 바이러스 전파가 매우용이한 환경이다. 철도차량의 경우도 예외는 아니며, 바이러스 확산 차단을 위해 다양한 노력을 기울이고 있지만, 근본적으로 철도차량의 난방 방식은 건조한 열풍을 강제로 순환시키는 공조 방식을 사용하고 있기 때문에 호흡기 바이러스에 매우 취약한 환경이다. 최근, 이를 해결하고자 철도차량 내장재로 사용되는 복합소재에 발열 기능을 추가하여 복사방식의 난방이 가능한 발열 복합재 라미네이트 개발 연구가 진행되었고 그성능을 입증한 바 있다. 하지만, 복합재의 장기간 발열 시 지속적인 고온에 노출되어 층간 분리나 결함 등의파손을 유발하고, 열적 혹은 기계적 성능에 영향을 미칠 가능성이 있다. 따라서, 본 연구에서는 선행연구에서개발된 발열 복합재 라미네이트 패널의 작동 내구성을 발열 성능 및 기계적 성능 관점에서 평가하였다.
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Investigation on the turbulent stress anisotropy of axisymmetric turbulence under rapid rotation
박주엽,정명균 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.3
The root cause of different oscillatory behavior of turbulent stress anisotropy under rapid rotation of initially axisymmetric turbulence is theoretically investigated. For this, based on the velocity spectral tensor of axisymmetric turbulence, the rapid part of the pressure-strain is determined and the equation of the turbulent stress anisotropy is solved for initial conditions generated by axisymmetric expansion and contraction of isotropic turbulence. As is well known, the damping of turbulent stress anisotropy under rapid rotation is observed for both initial conditions, and this feature is attributed to the linear rapid rotation effect on turbulence. On the other hand, the oscillatory development of turbulent stress anisotropy can be seen conspicuously only for the initial turbulence generated by axisymmetric expansion. This selective oscillatory feature is found to be strongly related to the total strain that is applied to the isotropic turbulence to generate the initial axisymmetric turbulence. And, through an asymptotic approach, it is also found that the material frame-indifference principle of two-dimensional turbulence is the underlying physics in this different oscillatory behavior.
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하절기 레일 온도 저감을 위한 차열직물의 제작 방법과 차열 성능의 상관관계 연구
박주엽,강동훈 한국정밀공학회 2024 한국정밀공학회지 Vol.41 No.4
Rails are important facilities related to safe running of trains. When buckling occurs due to thermal expansion, serious safety accidents such as train derailment can occur. Currently, operating organizations are building expensive temperature monitoring systems and automatic watering devices. However, they have limitations for universalization due to their costs. Recently, long-term rail temperature reduction effect has been demonstrated by applying thermal insulation paint to rail surface. However, when coating the rail surface with paint, it increases the difficulty of detecting defects through non-destructive testing, which is one of the important elements of rail maintenance. To solve this problem, previous studies have proposed a detachable thermal insulation fabric by coating the surface of a fabric with thermal insulation paint and attaching a magnetic material. In this study, effect of thermal insulation performance according to manufacturing method was analyzed to derive the optimal performance of the previously developed thermal insulation fabric. Experiment results confirmed that paint weight increased when the roller method was used compared to the spray method with temperature reduction performance improved. Finally, the most efficient and optimal paint weight ratio was derived when the roller method was applied.
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탄소섬유 발열체가 삽입된 철도차량용 복합재료 발열패널 제작 기술
박주엽,강동훈,구본용,이예진 한국철도학회 2022 한국철도학회논문집 Vol.25 No.7
Composite materials in the railroad field are rapidly expanding their application areas from leading-cap, roof, interior materials, etc., to car bodies and bogie frames. And, along with the expansion of the application of nanomaterials, research on composite materials in the railway field is expanding into various types of functionalization using the electrical and thermal properties of nanomaterials. On the other hand, the winter heating system currently used in railway vehicles is very vulnerable to spreading of respiratory infectious diseases such as COVID-19 by convection of hot air, so the need for a new heating technology is being raised. In this study, a composite material laminate panel manufacturing technology capable of generating heat was developed using a paper-type carbon fiber sheet. To this end, the resin infusion method was used to evaluate the effect of resin flow due to insertion of carbon fiber sheet during panel molding, and quantitative evaluation of the heating performance of the manufactured specimen was performed. As a result of the experiment, the applicability of a heat-generating composite material laminate panel to a new rail vehicle heating system was confirmed.
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발열 몰드가 적용된 레진 인퓨전 공법의 성형 품질 평가를 위한 광섬유 센서 적용 복합재 성형 모니터링
박주엽,강동훈 한국비파괴검사학회 2022 한국비파괴검사학회지 Vol.42 No.5
Composite materials are rapidly expanding their application to various fields owing to their excellent mechanical, electrical, and thermal performance. However, the high molding cost of composite materials compared with that of existing metal materials acts as an obstacle to the spread of composite materials, and various methods are being newly developed to improve it. In general, composite materials applied to interior parts for railway vehicles are produced in the form of a laminate panel using a vacuum thermoforming method. Because the vacuum thermoforming method uses a prepreg, an expensive material mixed with glass fiber and resin, the resin infusion method that directly injects resin into the glass fiber fabric, which is the raw material, has been suggested in prior studies to reduce material costs. However, even in the case of the resin infusion method, a facility such as a thermal chamber is essential for curing the resin; therefore, this study presents a new molding method that has improved it. Specifically, by applying a large-area planar heating element to the mold on which the fabric is laminated to give the mold a heating function, molding through direct heating of the mold in a room temperature environment is possible. Therefore, a new molding method that does not require a thermal chamber was proposed. In addition, to evaluate the molding quality of the presented method, cure monitoring using fiber Bragg grating sensors was performed, and the difference in molding quaility with the existing method was compared and analyzed. 복합재료는 우수한 기계적, 전기적, 열적 성능으로 다양한 분야로 그 적용이 빠르게 확대되고 있다. 하지만, 기존 금속재료 대비 복합재료의 높은 성형 비용은 복합재료 적용 확산의 걸림돌로 작용하여 이를 개선하고자 다양한 공법이 새롭게 개발되고 있다. 일반적으로 철도차량용 복합재료 내장재 부품의 제작은 진공 열성형 공법을 이용해 라미네이트 패널 형태로 제작된다. 진공 열성형 공법은 유리섬유와 수지가 혼합된 고가의 재료인 프리프레그를 이용하므로 재료비 절감을 위해 원재료에 해당하는 유리섬유 직물에 수지를 직접 주입하는 레진 인퓨전 공법이 선행 연구를 통해 제시된 바 있다. 하지만, 레진 인퓨전 공법의 경우에도 수지의 경화를 위해서는 열 챔버와 같은 시설이 필수적으로 요구되므로, 본 연구에서는 이를 개선한 새로운 성형 공법을 제시하고자 한다. 구체적으로, 직물이 적층되는 몰드에 대면적 면상 발열체를 적용하여 몰드에 발열 기능을 부여함으로써 상온 환경에서 몰드의 직접 발열을 통한 성형이 가능하여 열 챔버가 필요없는 새로운 성형 방법을 제시하였다. 또한, 제시된 방법의 성형 품질 평가를 위해 광섬유 브래그 격자 센서를 이용한 성형 모니터링을 수행하였으며 기존 공법과의 성형 품질 차이를 비교 분석하였다.
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