• Title/Summary/Keyword: 박리영역

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Characteristics of Falling Weight Impact Responses due to Stacking Sequences of CF/Epoxy Composite Plates (CF/Epoxy 복합평판의 적층구성에 따른 낙추충격특성에 관한 연구)

  • 박노식;임광희;김기형;양인영
    • Composites Research
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    • v.13 no.6
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    • pp.30-38
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    • 2000
  • In this paper, a system of falling weight impact tester was built up to evaluate the impact energy absorbing characteristics and impact strength of CFRP laminate plates in consideration of stress wave propagation theory. Delamination area of impacted specimens for the different ply orientation was measured with ultrasonic C-scanner to find correlation between impact energy and delamination area. Absorbed energy of quasi-isotropic specimen having four interfaces was higher than that of orthotropic laminates with two interfaces. The more interfaces, the more absorbed energy. Hybrid specimen containing GFRP layer was higher than that of normal specimens.

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Quantitative Evaluation of Flaw by Ultrasonic Spectroscopy (초음파 주파수 분석법에 의한 결함의 정량적 평가에 관한 연구)

  • 한응교;김성규;박준서;이범성;박익근
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.5
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    • pp.1004-1010
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    • 1992
  • In recent years, along with the development of ultrasonic probe with wide frequency range, the digitization of measuring instrument, and the development of operating process technics, it is possible to analyze ultrasonic pulse in frequency range. In this paper, applying to flaw model the ultrasonic spectroscopy method that can analyze ultrassonic pulse in frequency range, we examine the possibility of quantification of flaw and apply its result to the void and seperation in LSI package. Consequently, by using the change in frequency distribution and central frequency of sltrasonic pulse detected from flaw, the estimation of shape, size, and depth of flaw is possible. The change in central frequency is changed minutely by the sample materals and position of flaw, but changed mainly by the shape and size of flaw. And we can quantify the shape and size of flaw in LSI pakcage using the experimental result through flaw model.

Comparative Photoluminescence Study of Single-Layer MoS2 Annealed in Hydrogen and Vacuum

  • Ryu, Ye-Jin;Park, Min-Gyu;Ryu, Sun-Min
    • Proceedings of the Korean Vacuum Society Conference
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    • 2014.02a
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    • pp.195.1-195.1
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    • 2014
  • 최근 반자성 물질인 $MoS_2$를 수소 기체 속에서 열처리하게 되면 약한 강자성이 유발된다는 연구가 보고되었다. 본 연구에서는 강자성 발현을 수반하는 물리적 및 화학적 변화를 이해하기 위해서 단일층 $MoS_2$에 대한 라만분광 및 광발광 연구를 수행하였다. 기계적 박리법을 이용하여 $MoS_2$ 결정으로부터 단일층 및 이중층 $MoS_2$를 분리하여 $SiO_2/Si$ 기판에 전사한 후, $200^{\circ}C{\sim}500^{\circ}C$ 영역의 특정 온도에서 1시간 동안 열처리하였다. 배경 기체가 열처리 도중 $MoS_2$에 미치는 영향을 이해하기 위하여 수소 속 반응을 진공 상태와 비교하였다. 라만 스펙트럼에서는 큰 변화가 없었으나, 광발광의 세기는 수소 속 반응 후에 감소하고 진공 속 반응 후에는 증가하는 대조적인 결과를 보였다. AFM 측정으로부터는 열처리 후에 $MoS_2$ 표면에 뚜렷한 변화가 일어나지 않는다는 사실을 확인하였다. 본 발표에서는 수소와 진공 조건에서 관찰된 상이한 광발광 특성과 그래핀/$SiO_2/Si$에서 관찰된 p-형 도핑과의 상관관계를 설명하고자 한다.

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Application of PIV in the Flow Field Over a Fixed Dune Bed (언덕이 있는 하상유동 계측을 통한 PIV기법의 수력학적 적용연구)

  • Hyun B. S.;Balacharldar R.;Patel V, C.
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.5 no.3
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    • pp.10-15
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    • 2002
  • The assessment of PIV to measure the mean velocity and turbulence was carried out over a train of fixed two-dimensional dunes. The agreement between the PIV and LDV is good enough even in regions of flow reversals and high shear. Though limited in the wall normal direction field-of-view, PIV provides instantaneous flow fields, which reveal the complex nature of flow over dunes, as well as more sophisticated analyses such as two-point space correlation and quadrant analysis with a reasonable accuracy The present study is expected to be directly applied to more complex flow such as sediment transport.

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합성 그래핀을 이용한 김서림 방지 필름 제작

  • Lee, Byeong-Ju;Jeong, Gu-Hwan
    • Proceedings of the Korean Vacuum Society Conference
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    • 2011.08a
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    • pp.357-357
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    • 2011
  • 그래핀은 육각형 구조로 이어진 탄소원자가 단일층을 형성한 현존하는 가장 얇은 나노물질로서, 면상에서의 우수한 전기적 열적 전도도와 화학적 안정성 등으로 많은 주목을 받고 있다. 이러한 그래핀의 우수한 특성들은 뛰어난 기계적 특성 및 높은 광 투과성과 맞물려 향후 플렉서블 투명전도막 등으로의 응용이 기대되고 있는 상태이다. 이러한 그래핀을 얻는 방법에는 물리 화학적 박리법, 산화규소의 흑연화, 열화학기상증착법(CVD) 등 많은 방법들이 존재하는데, 이중 CVD방법이 대면적으로 두께 균일도가 높은 그래핀을 얻는데 가장 적합한 방법으로 알려져 있다. 본 연구에서는 CVD방법을 이용하여 합성한 그래핀을 투명글래스 위에 전사하는 공정을 통하여 김서림방지(antifogging) 필름을 제작하였고, 그 면 발열특성에 대하여 조사하였다. 메탄가스를 원료가스로 합성한 그래핀 투명막은 가시광 영역에서 80% 이상의 투광도와 500~600 ${\Omega}/sq$ 정도의 면저항을 나타내었다. 또한 금 나노입자 또는 플라즈마 도핑 등의 후처리 공정을 통하여 면 발열특성의 향상을 도모하였으나 합성상태의 그래핀을 이용하는 것이 가장 우수한 면발열특성을 나타낸 것으로 확인하였다. 본 연구결과는 겨울철 자동차 유리표면의 성에 제거 등의 응용에 유용할 것으로 기대된다.

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A Study on the Mass Transfer from a Square Cylinder Using Naphthalene Sublimation Technique (나프탈렌승화법을 이용한 사각관 주위에서의 물질전달에 관한 연구)

  • 유성연
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.5
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    • pp.1300-1310
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    • 1990
  • Naphthalene sublimation technique is employed to investigate the mass transfer processes from a square cylinder at various Reynolds numbers and various angles of attack. Distribution of the local mass transfer coefficients on each face of the cylinder changes dramatically with the angle of attack. Such variation of local mass transfer rates closely connected with the complex flow phenomena such as stagnation, acceleration, separation, reattachment and vortex shedding. The average Sherwood number has a minimum value at 12.deg.-13.deg., and a maximum value at a=20.deg.-25.deg. A comparison of present mass transfer measurement with other heat transfer measurements, using the heat/mass transfer analogy, shows good agreement in average transfer rates, same trend but notable differences in local values. Therefore, naphthalene sublimation technique can be adopted to explore heat transfer processes in the complex flow situations, which is considered to be hardly possible with the conventional heat transfer measurements.

Heat/Mass Transfer Measurements on a Film Cooled Blade with Naphthalene Saturated Coolant (나프탈렌 포화공기가 분사되는 막냉각 홀을 가진 터빈 블레이드 표면의 열/물질전달 계수 측정)

  • Lee, Dong-Hyun;Rhee, Dong-Ho;Kim, Kyung-Min;Cho, Hyung-Hee;Kim, Beom-Su
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2010.05a
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    • pp.433-436
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    • 2010
  • In this paper, heat/mass transfer characteristics on a film cooled stationary rotor blade are investigated using the naphthalene sublimation method. A row-speed annular wind tunnel with a single annular turbine stage is used. Three rows of film cooling holes are machined on the leading edge of the test blade. Detailed heat/mass transfer distributions are measured with changing the blowing rate from 1.0 to 2.0. As the blowing ratio increases, overall heat/mass transfer increases and the lower peak formed on the pressure side were disappeared.

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A Numerical Study on Flow Characteristics of Second Throat Exhaust Diffuser with Shock Cone Shape (램 구조물 형상에 따른 이차목 디퓨저의 유동 특성에 관한 수치적 연구)

  • Yu, Seongha;Jo, Seonghwi;Kim, Hongjip;Ko, Youngsung;Na, Jaejeong
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2017.05a
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    • pp.346-351
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    • 2017
  • A numerical study has been conducted to investigate flow characteristics of STED with ram structure shape. By increasing the attack angle of shock cone, vacuum pressure is increased because of oblique shock at ram structure and separation point moved to the downstream of the second throat. By increasing blockage ratio, expansion wave angle is increased at ram structure while vacuum pressure is constant.

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Dynamic Stall Control with Droop Leading Edge and Gurney Flap (앞전 Droop과 Gurney 플랩을 이용한 동적 실속 제어)

  • Lee, Bo-Sung;Yee, Kwan-Jung;Joo, Wan-Don;Lee, Dong-Ho
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.32 no.5
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    • pp.10-17
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    • 2004
  • To achieve the advanced forward flight performance of helicopter, the passive control methods for enhancement of the dynamic stall characteristics of rotor blades are studied. To enhance the dynamic stall characteristics of the rotor blades, it is essential to improve the lift performance and the pitching moment performance simultaneously with the control of the separation on the rotor blades. For this point of view, both the fixed droop leading edge and the Gurney flap which are simply realized are used for control of the dynamic stall in severe dynamic stall conditions. From this study, the combination of both passive control methods showed dramatic enhancement of lift and pitching moment performance in dynamic stall than previous research results.

Intake Flow Characteristics of HyShot Scramjet Engine (HyShot 스크램제트 엔진의 흡입구 유동특성 연구)

  • Won Su-Hee;Choi Jeong-Yeol;Jeung In-Seuck
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2004.10a
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    • pp.47-52
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    • 2004
  • In the design of scramjet intake for hypersonic flight, a variety of aerothermodynamics phenomena are encountered. These phenomena include blunt leading - edge effects, boundary layer development issues, transition, inviscid / viscous coupling, shock - shock interactions, shock / boundary - layer interactions, and flow profile effects. For intakes that are designed to operate within a narrow Mach number / altitude envelope, an understanding of a few of these phenomena might be required. In this work several predominant flowfield phenomena (viscous phenomena, boundary - layer separation, and combustor entrance profile) are discussed to investigate the performance of the intake at the altitude and angle of attack extremes of the HyShot flight experiment.

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