• Title, Summary, Keyword: 복합하중

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Effects of Specimen Geometry on Stress Distribution in Sandwich Specimen Under Combined Loads (복합하중을 받는 샌드위치 시편의 응력분포에 미치는 시편 형상의 영향)

  • Park, Su-Kyeong;Hong, Sung-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.11
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    • pp.1587-1592
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    • 2010
  • The effects of specimen geometry and loading conditions on the stress distribution in a sandwich specimen under combined loads are investigated by elastic finite element analysis. A commercial software NASTRAN is used in plain-strain two-dimensional finite element analysis of sandwich specimens; the analysis was performed for three different specimen shape factors and four different combined displacement conditions. The results of computational analysis suggest that the effect of the combined displacement angle, which is defined as the ratio of the shear displacement to the normal displacement, on the size of the non-homogeneous stress distribution is observed only in the case of the shear stress and von Mises stress. Also as the combined displacement angle increases, the size of the nonhomogeneous stress distribution decreases in the case of the shear stress and increases in the case of the von Mises stress. In addition, as the specimen shape factor, which is defined as the ratio of the specimen length to the height, increases, the size of the non-homogeneous stress distribution under combined displacement conditions decreases significantly.

A Study on the Prediction of the Loaded Location of the Composite Laminated Shell by Using Neural Networks (신경회로망을 이용한 복합재료 원통쉘의 하중특성 추론에 관한 연구)

  • 명창문;이영신;류충현
    • Composites Research
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    • v.14 no.5
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    • pp.26-37
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    • 2001
  • After impact analysis of the composite cylindrical shells was performed. obtained outputs at 9 equally divided points of the shell were used as input patterns of the neural networks. Identification of impact loading characteristics was predicted simultaneously. Momentum backpropagation algorithm of neural networks which can modify the momentum coefficient and learning rate was developed and applied to identify the loading characteristics. Hidden layers of the backpropagation increased from 1 layer to 3 layers and trained the loading characteristics. Developed program with variable learning rate was converged close to real load characteristics under 1% error. Inverse engineering which identify the impact loading characteristics can be applicable to the composite laminated cylindrical shells with developed neural networks.

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Crippling Test of Z-section Graphite/Epoxy Stringers (Z-단면 Graphite/Epoxy 스트링거의 크리플링 실험)

  • 최상민;권진희
    • Composites Research
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    • v.14 no.3
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    • pp.32-41
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    • 2001
  • Z-section composite stringers with various lengths and flange-widths are tested in axial compression for the validation of a finite element algorithm to calculate the buckling and crippling stresses of composite laminated stringers. The stacking sequence considered is $[{\pm}45/0/90]s$. Strain gages are attached to each specimen, and deflection and end-shortening are obtained by two LVDTs. The buckling load is determined from the load vs. strain response, load vs. end-shortening curves, and load vs. out-of-plane deflection curves. The ultimate stress after local buckling is used as the crippling stress. Comparison between finite element and experimental results shows good agreement in the local buckling and crippling stresses.

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Buckling Behavior of Transversely Isotropic Composite Shells Subjected to Axial Compression (축방향 압축 하중을 받는 횡등방성 복합재료 쉘의 좌굴거동)

  • 김성도;정진환
    • Computational Structural Engineering
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    • v.11 no.3
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    • pp.229-239
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    • 1998
  • 복합재료는 강도-무게비가 다른 재료들에 비해 훨씬 크기 때문에 부재의 좌굴문제가 대단히 중요하게 취급되며, 본 논문에서는 축방향 압축력을 받는 복합재료로 된 쉘 부재의 좌굴해석이 수행된다. 이 재료는 일반적으로 이방성 재료 특성을 나타내 보이나, 섬유들이 한 방향으로만 배치되어 있는 경우 섬유방향에 연직한 평면에서의 강도나 탄성계수들은 모두 일정한 횡 등방성 재료성질을 가진 것으로 간주할 수 있다. 9 절점 degenerate 쉘 유한요소를 사용한 선형안정해석, LUSAS 범용 프로그램을 이용한 구조해석, 그리고 고전적 쉘 좌굴방정식에 의한 해석들을 수행하였으며, 그 결과들을 서로 비교, 분석하였다. 고려된 등방성 재료나 횡 등방성 재료의 경우 모두, degenerate 유한요소해석으로 계산한 임계하중들은 고전적 이론해에 의한 결과들 보다 낮았으며, LUSAS 결과들과는 거의 같았다. 이는 degenerate 유한요소에 의한 선형안정해석 결과들이 안전측에 듬을 의미하며, 복합재료로 된 쉘 구조물의 좌굴해석에 degenerate 유한요소를 효율적으로 적용할 수 있음을 의미한다.

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Estimation of Dynamic Response of Advanced Composite Material Decks for Bridges Application under Various Vehicle Driving Velocities (복합재료 교량 바닥판의 주행속도에 따른 동적응답 평가)

  • 천경식;장석윤
    • Composites Research
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    • v.16 no.6
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    • pp.23-32
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    • 2003
  • Applications of advanced composite material in construction field are tending upwards and development of all composite material bridges is making progress rapidly in home and abroad due to their high strength to weight ratio. This paper formulated the dynamic responses of the laminated composite structures subjected to moving load and analyzed the various dynamic behaviors using the finite element method. The nondimensionalized natural frequencies of a simply supported square-laminated composite plate are considered for verifications. Mode superposition and Newmark direct integration method are applied for moving load analysis. For structural models, dynamic magnification factor calculated for various velocities of the moving load and displacements characteristics of laminated composite structures due to the moving load are investigated theoretically Numerical results are presented to study the effects of lamination scheme, stacking sequence, and fiber angle for laminated composite structures during moving load. The various results on moving load and lamination through numerical analysis will present an important basic data for development and grasp the behavior of all composite material bridges.

The effect of random spectrum on the fatigue life of hybrid metal matrix composites (랜덤하중이 하이브리드 금속복합재료의 피로수명에 미치는 영향)

  • 김성훈;배성인;송정일
    • Composites Research
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    • v.16 no.6
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    • pp.48-55
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    • 2003
  • This research makes comparisons of empirical fatigue-lives between AC8A A1 alloy and the metal matrix composites(A1/A12O3, A1/A12O3/A12O3p), and also includes comparisons of fatigue-lives between empirical fatigue-lives and estimated fatigue-lives from regular-periodic load testing, AE method to predict fatigue-crack initiation before visible in sight and SEM(scanning electron microscope) photographs of each material. According to the test results of the notched specimen. the fatigue life of the hybrid metal matrix composites and the metal matrix composites, which are more brittle than the base matrix was shorter than that of the base matrix under both types of loads. In addition, the fatigue-life estimated from the damage summation method and that from experiments at random loads were fairly identical.

Stacking Sequence Design of Fiber-Metal Laminate Composites for Maximum Strength (강도를 고려한 섬유-금속 적층 복합재료의 최적설계)

  • 남현욱;박지훈;황운봉;김광수;한경섭
    • Composites Research
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    • v.12 no.4
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    • pp.42-54
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    • 1999
  • FMLC(Fiber-Metal Laminate Composites) is a new structural material combining thin metal laminate with adhesive fiber prepreg, it nearly include all the advantage of metallic materials, for example: good plasticity, impact resistance, processibility, light weight and excellent fatigue properties. This research studied the optimum design of the FMLC subject to various loading conditions using genetic algorithm. The finite element method based on the shear deformation theory was used for the analysis of FMLC. Tasi-Hill failure criterion and Miser yield criterion were taken as fitness functions of the fiber prepreg and the metal laminate, respectively. The design variables were fiber orientation angles. In genetic algorithm, the tournament selection and the uniform crossover method were used. The elitist model was also used to be effective evolution strategy and the creeping random search method was adopted in order to approach a solution with high accuracy. Optimization results were given for various loading conditions and compared with CFRP(Carbon Fiber Reinforced Plastic). The results show that the FMLC is more excellent than the CFRP in point and uniform loading conditions and it is more stable to unexpected loading because the deviation of failure index is smaller than that of CFRP.

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Viscoelastic Bending Behaviors of Unidirectional Fiber Reinforced Composite C-rings with Asymmetric Material Properties (비대칭물성을 고려한 일축방향 섬유강화 복합재료 C링의 점탄성적 거동해석)

  • 이명규;이창주;박종현;정관수;김준경;강태진
    • Composites Research
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    • v.13 no.5
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    • pp.18-30
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    • 2000
  • In order to optimize the design of unidirectional fiber reinforced composite C-rings, a viscoelastic load relaxation behavior was analyzed under a point load. Initially, the deflection and bending stiffness were calculated based on the elastic beam theory and the viscoelastic relaxation and creep behaviors were derived from the elastic solution using the correspondence theorem. Besides the orthotropic mechanical properties of the composite, asymmetric mechanical property due to the different tensile and compressive properties were also considered. Except the deviation affected by the relatively large thickness of the specimen compared to the radius, the calculated relaxation showed good agreement with the experimental result.

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Vibratory Hub Loads of Helicopters due to Uncertainty of Composite Blade Properties (복합재료 블레이드의 불확실성을 고려한 헬리콥터 허브 진동하중 해석)

  • You, Young-Hyun;Jung, Sung-Nam
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.7
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    • pp.634-641
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    • 2009
  • In this work, the behavior of vibratory hub loads induced due to the uncertainties of composite material properties for each of the participating rotor blades is investigated. The random material properties of composites available from the existing experimental data are processed by using the Monte-Carlo simulation technique to obtain the stochastic distribution of sectional stiffnesses of composite blades. The coefficients of variation (standard deviation divided by the mean) obtained from the sectional stiffness constants are used as an input to the comprehensive aeroelastic analysis code that can evaluate the hub loads of a rotor system. It is found that the uncertainty effects of composite material properties inevitably bring a dissimilarity to the rotor system. The influence of hub vibration response with respect to the individual stiffness (flatwise bending, chordwise bending and torsion) changes is also identified.

Nonlocal Peridynamic Models for Dynamic Brittle Fracture in Fiber-Reinforced Composites: Study on Asymmetrically Loading State (섬유강화 복합재의 동적 취성 파괴현상 규명을 위한 비국부 페리다이나믹스 해석법 개발: 비대칭 하중 연구)

  • Ha, Youn Doh;Cho, Seonho
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.25 no.4
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    • pp.279-285
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    • 2012
  • In this paper a computational method for a homogenized peridynamics description of unidirectional fiber-reinforced composites is presented. For these materials, dynamic brittle fracture and damage are simulated with the proposed peridynamic model. Compared with observations from dynamic experiments by Coker et al.(2001), the peridynamic computational model can reproduce various characteristics of dynamic fracture and supersonic or intersonic crack growth in asymmetrically loaded unidirectional fiber-reinforced composite plates. Also we analyze the same model in the symmetric loading condition and figure out that the asymmetric loading leads to a much higher propagation speed. Consistent results have been reported in the experiments.