• Title, Summary, Keyword: 복합하중

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Refined Decoupled Stress Analysis for Thermo-piezoelectric Composite Plate (열-전기-기계 하중에서의 복합재 평판의 응력해석)

  • 오진호;조맹효
    • Proceedings of the Korean Society For Composite Materials Conference
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    • pp.46-49
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    • 2000
  • A decoupled thermo-~lezoelectric-mechanical model of composite laminates with surface bonded piezoelectric actuators, subjected to externally applied load, temperature change load, electric field load is developed. The governing differential equations are obtained by applying the principle of free energy and variational techniques. A higher order zigzag theory displacement field is employed to accurately capture the transverse shear and normal effects in laminated composite plates of arbitrary thickness.

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A Study on Tensile Properties of CFRP Composites under Cryogenic Environment (극저온 환경에서 탄소섬유강화 복합재의 인장 물성에 관한 연구)

  • Kim Myung-Gon;Kang Sang-Guk;Kim Chun-Gon;Kong Cheol-Won
    • Composites Research
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    • v.17 no.6
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    • pp.52-57
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    • 2004
  • In this study, mechanical tensile properties of carbon fiber reinforced polymeric (CFRP) composite cycled with thermo-mechanical loading under cryogenic temperature (CT) were measured using cryogenic environmental chamber. Thermo-mechanical tensile cyclic loading (up to 10 times) was applied to graphite/epoxy unidirectional laminate composites far room temperature (RT) to $-50^{\circ}C$, RT to $-100^{\circ}C$ and RT to $-150^{\circ}C$. Results showed that tensile stiffness obviously increased as temperature decreased while the thermo-mechanical cycling has little influence on it. Tensile strength, however, decreased as temperature down to CT while the reduction of strength showed little after CT-cycling. For the analysis of the test results, coefficient of thermal expansion (CTE) of laminate composite specimen at both RT and CT were measured and the interface between fiber and matrix was observed using SEM images.

Micromechanical Analysis for Transverse Properties of Ceramic/Metal Composite (세라믹/금속기지 복합재료의 특성예측을 위한 미시역학적 유한요소해석)

  • 김태우;박상환
    • Journal of the Korean Ceramic Society
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    • v.38 no.6
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    • pp.575-581
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    • 2001
  • 세라믹/금속기지 복합재료에서 횡방향의 단축인장하중을 받는 경우, 복합재료의 특성에 관한 시뮬레이션 결과이다. 세라믹과 금속기지간 계면에 강한 결합이 존재하는 복합재와, 계면에서의 결합이 약한 복합재의 두 경우에 대하여 횡방향 평균응력과 평균변형율에 대한 관계를 계산하였다. 복합재료의 미시역학적개념과 유한요소해석법을 적용하여 세라믹체적분율의 변화에 따라 각기 해석되었다. 본 연구에서 계산된 횡방향 탄성계수는 문헌에 알려져 있는 미시역학개념으로 유도된 식에 의한 횡방향탄성계수값과 잘 일치되었다. 계면에서 강한 결합이 있는 복합재와는 달리, 약한 결합의 복합재는 인장하중에 의하여 세라믹/금속계면에서 금속재료와 세라믹간의 분리가 발생된다. 이 분리는 전체복합재의 강성을 감소시키며, 금속의 부피분율이 감소될수록 (즉, 세라믹의 부피분율이 증가할수록) 횡방향 평균응력의 평균변형율에 대한 감소로 나타났다. 미시역학의 개념을 적용한 유한요소해석기법을 통하여, 이미 알고 있는 복합재 각 성분의 특성으로부터 복합재료의 계면특성과 횡방향특성을 예측할 수 있다.

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Prediction of Fatigue Life for Composite Rotor Blade of Multipurpose Helicopter Using Strength Degradation Model (강도저하모델을 이용한 다목적헬리콥터용 복합재로터깃 피로수명예측)

  • 권정호;서창원
    • Composites Research
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    • v.14 no.2
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    • pp.50-59
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    • 2001
  • The predictions of residual strength evolution and fatigue life of full scale composite rotor blade for multipurpose helicopter were studied using a strength degradation model. Flight-by-flight load spectrum was developed on the basis of FELIX standard spectrum data. The laminated structural analysis was also performed to obtain corresponding local stress and/or strain spectra for each ply of laminate skin and glass roving spar structures around the blade root where fatigue damage was severely anticipated.

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複合構造의 結合

  • 홍창선
    • Journal of the KSME
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    • v.22 no.1
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    • pp.9-14
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    • 1982
  • 복합재료를 이용하여 부품제작을 한 후 어떠한 결합방법을 채택할 것인가를 결정할 때 고려해 야할 점을 기계적 결합법과 접착결합법을 비교하여 검토하였다. 기계적 결합은 하중을 많이 받고 분해 및 결합이 자주 예상되는 부품에 채택해야 할 것이며 복합재료의 특성을 고려하여 보강 시에 부착하는 평판의 섬유방향은 가급적 드릴구멍주위를 부드럽게 하여 응력집중을 낮출 수 있으며 하중의 종류에 따라 적층의 섬유방향을 조절함으로서 응력집중을 조절할 수 있다. 드릴 구멍 주위인 파손은 평판의 폭과 구멍의 직경등이 크게 작용함으로 강도해석을 할 경우에 응력 해석을 한 후 허용응력등을 결정해야할 것이다. 접착졀합법은 작업이 간단하나 신뢰도가 떨어지 므로 하중을 많이 받는 구조물에의 사용에 주의를 요하며 설계방법도 매우 다양하게 제안되어 있어 선택함에 있어 하중 환경조건등을 점검해야할 것이다. 접착결합법은 드릴구멍같은 불연속 성을 갖지 않기 때문에 응력집중이 생기지 않으나 접착층의 길이등 기하학적 형상에 따라 다르게 나타남으로 잡착층의 분리가 일어나지 않도록 설계되어야 한다. 특히 복합재료의 이방성인 성 질을 감안하여 접착층에 이웃하는 피접착층의 섬유방향에 주의해야 하며 층간응력이 파손에 미 치는 영향을 고려하여 설계에 임해야 한다.

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An Experimental Study on the Hybrid Composite Carbody Structure (하이브리드 복합재 철도차량 차체에 대한 시험적 연구)

  • Kim Jung-Seok;Jeong Jong-Cheol;Lee Sang-Jin
    • Composites Research
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    • v.18 no.6
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    • pp.19-25
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    • 2005
  • This paper has performed an experimental study on the hybrid composite carbody of Korean tilting railway vehicle. The hybrid composite carbody has the length of 23m and is comprised of a 40mm-thick aluminium honeycomb core and 2mm-thick woven fabric carbon/epoxy face sheet. In order to evaluate the structural behavior and safety of the hybrid composite carbody, the static load tests such as vertical load, end compressive load, torsional load and 3-point support load tests have been conducted. The test was performed under Japanese Industrial Standard (JIS) 17105 standard. from the tests, the maximum deflection was 12.3mm and the equivalent bending stiffness of the carbody was $0.81\times10^{14}\;kgf{\cdot}mm^2$. The maximum strain of the composite body was below $20\%$ of failure strain of the carbon/epoxy face sheet.

Studies on Probabilistic Nonlinear First Ply Failure Loads and Buckling Loads of Laminated Composite Panels (적층복합재료 패널의 확률론적 비선형 초기파단하중 및 좌굴하중에 관한 연구)

  • Bang, Je-Sung
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.17 no.6
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    • pp.1-10
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    • 2013
  • Probabilistic nonlinear first ply failure loads of flat composite panels and nonlinear buckling loads of curved composite panels with cutouts are estimated to provide the more reliable main load carrying structure in the renewable energy industry and offshore structures. The response surface method approximates limit state surface to a second order polynomial form of random variables with the results of deterministic finite element analyses at given sampling design points. Furthermore, the iterative linear interpolation scheme is used to obtain a more accurate approximation of the limit state surface near the most probable failure point (MPFP). The advanced first order second moment method and the Monte Carlo method are performed on an approximated limit state surface to evaluate the probability of failure. Finally, the sensitivity of the reliability index with respect to transformed random variables is investigated to figure out the main random variables that have an effect on failures.

Nonlinear Random Vibration of Laminated Composite Plates by Comparison of Classical Theory, 1st and 3rd Order Shear Theories (복합적층판의 비선형 불규칙 진동 해석에 관한 고전 이론, 1차 및 3차 전단 이론의 비교 연구)

  • Kang, Joowon
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.13 no.1
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    • pp.129-138
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    • 2000
  • Composites are finding increasing use in a wide variety of engineering applications due to their outstanding mechanical properties. A number of studies have focused on the development of new materials as well as the response of composite structures to static and dynamic loads by assuming the external driving forces to be deterministic. However, there ate many situations in practice where the exciting forces vary randomly. In this work, the nonlinear response of laminated composite plates excited by stochastic loading is studied by the finite element method. Classical, first-order and third-order shear theories for plates are used in the finite element formulation. Since most composites exhibit significant nonlinearity in the shear stress-strain law, this is included in the present analysis.

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A Study on the strength of mechanically fastened composite joint using the failure area index method (파괴면적지수법을 이용한 복합재료 기계적 체결부의 강도평가에 관한 연구)

  • 전영준;최진호;권진회
    • Composites Research
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    • v.16 no.5
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    • pp.1-6
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    • 2003
  • As the use of composites has become popular in recent years, the design of the composite joints has become a very important research area because the structural efficiency of the composite structure is determined by its joints, not by its basic structures. In this paper, presented comparisons of numerical results by the FAI(Failure area index) method[9] and measured data for a various geometric shapes and stacking sequence justify the validity of the FAI method. The FAI method is shown to produce very favorable comparisons with measured failure loads of mechanically fastened composite joints with the difference well within 9.96% for all II cases investigated.

Microcracking of Motor Case with Fiberite 934/T300 Laminates under fatigue Loads (피로하중을 받는 Fiberite 934/T300 복합재료로 만들어진 연소관의 미세균열 연구)

  • 김형원;김성은
    • Journal of the Korean Society of Propulsion Engineers
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    • v.1 no.1
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    • pp.82-88
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    • 1997
  • The goal is to assess the effect of fatigue loading on mechanical properties of Fiberite 934/T300 laminates of pressure vessel using the recent variational mechanics analysis. This analysis has been useful in providing fracture mechanics interpretation of matrix microcracking in cross-ply laminates. This paper describes using the new energy release rate analysis for a fracture mechanics based interpretation of microcrack formation during fatigue loading. The master plot by modified Paris-law gives a complete characterization of a material system's resistance to microcrack formation.

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