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황영은(Youngeun Hwang),윤성호(Sungho Yoon) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
In this study, the absorption behaviours of carbon/epoxy composite were experimentally investigated through salt-water absorption tests and its theoretical investigation was also performed to compare the experimental results. In order to perform the absorption test of the composite under salt-water environments, the specimens were subjected to temperatures of 35, 55, and 75℃ for 730 days. According to the results of absorption tests, the curves of moisture content represented linear Fickian behaviour and its moisture diffusion coefficient increased at higher exposure temperature. The curves of moisture content derived from theoretical equation followed the experimental results. Using the activation energy and diffusion constant calculated from Arrhenius equation, the curve of moisture content at room temperature was derived and its exposure time to reach equilibrium was then determined.
황영은(Youngeun Hwang),오진오(Ohjin Oh),윤성호(Sungho Yoon) 한국추진공학회 2009 한국추진공학회 학술대회논문집 Vol.2009 No.11
본 연구에서는 기존의 접착제를 대체용 접착제로 대체 가능한지의 여부를 조사하기 위하여 구조용 접착제에 대해 일련의 열화 시험을 수행하였다. 구조용 접착제는 온도, 수분, 자외선 등의 자연환경 조건을 모사할 수 있는 가속노화시험기를 통해 복합적인 환경인자에서 1000시간 동안 노출시켰다. 구조용 접착제의 기계적 특성은 하중 시험기를 통해, 화학적 특성은 적외선 분광 분석 장치를 통해 평가하였다. 연구결과에 따르면 대체용 접착제가 환경인자에 노출될 경우 기존의 접착제에 비해 안정적이기 때문에 기존의 접착제는 대체용 접착제로 대체 가능할 것으로 판단하였다. In this study, a series of degradation test for structural adhesives was performed to investigate the possibility of replacement of the alternative adhesives to the conventional adhesives. Four types of the adhesives were exposed to combined environmental conditions over 1000 hours at an accelerated aging tester, which can simulate natural weather conditions such temperature, moisture and ultraviolet. Mechanical and chemical properties of the adhesives were evaluated through material testing system and FT/IR spectrometer. According to the results, the conventional adhesives can be replaced by the alternative adhesives because the alternative adhesives were more stable to environmental conditions rather than the conventional adhesives.
김찬규,황영은,Kim, Changyu,Hwang, Youngeun 한국군사과학기술학회 2017 한국군사과학기술학회지 Vol.20 No.4
In this paper, impact characteristics of a water entry gliding vehicle were analyzed using a finite element method. To guarantee the validity of analysis results, a convergence test was performed for several ratios of Euler and Largrange mesh sizes. The impact coefficient was calculated with respect to entry angles and angle of attacks. It can be observed that the impact coefficient was large at a high cross-section gradient and was also affected by cavitation. This study could be useful in the preliminary design stage of a water entry bomb development.
김찬규(Changyu Kim),황영은(Youngeun Hwang),윤성호(Sungho Yoon) 한국추진공학회 2013 한국추진공학회지 Vol.17 No.2
This research analyzed the acoustic emission signals collected from the pin loading tests and investigated the effect of hygrothermal exposure on the fracture behavior of the pin-jointed carbon fiber/epoxy composites. The composite specimens include: the Base specimen that has not been exposed to any environments, the RT specimen that has been immersed in room temperature water, and the HT specimen that has been immersed in high temperature water. According to the pin loading test, the RT and the HT specimens showed 2.2% and 13% decreases in the bearing strength compared to the Base specimen, respectively. The analysis of the acoustic emission signals showed different fracture acceleration points for three types of the specimens. Furthermore, for the RT and the HT specimens, the event from the matrix crack signals in the composites decreased. This shows the effect of the hygrothermal conditions on the acoustic emission signals. Additionally, upon investigating the fracture behaviors of the pin-jointed composites, the exposing specimens to hygrothermal environments decreases the interfacial characteristics of the composites.