• Title/Summary/Keyword: fiber waviness

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Stress and Strain Distribution of Thick Composites with Various Types of Fiber Waviness under Tensile and Compressive Loadings (다양한 형태의 보강섬유 굴곡을 가지는 두꺼운 복합재료의 인장/압축 하중 하에서의 응력/변형률 분포)

  • 신재윤;이승우;전흥재
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2000.04a
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    • pp.97-100
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    • 2000
  • A FEA(finite element analysis) model was proposed to study stress and strain distributions in thick composites with various types of fiber waviness under tensile and compressive loadings. Three types of model were considered in this study: uniform fiber waviness, graded fiber waviness and localized fiber waviness models. In the analysis, both material and geometrical nonlinearities due to fiber waviness were incorporated into the model utilizing energy density and incremental method. The strain distributions of uniform fiber waviness model were strongly influenced whereas the stress distributions were little influenced by fiber waviness. The stress and strain distributions of graded and localized fiber waviness models showed more complex distributions than those of uniform fiber waviness model due to the variation of fiber waviness along the thickness and length directions. It was concluded that the stress and strain distributions of composites with fiber waviness were significantly affected by types of fiber waviness.

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Strength Prediction of Thick Composites with Fiber Waviness under Tensile/Compressive Load Using FEA (인장/압축 하중 하에서 FEA를 이용한 굴곡진 보강섬유를 가진 두꺼운 복합재료의 강도예측에 관한 연구)

  • 류근수;전흥재
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2001.10a
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    • pp.129-132
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    • 2001
  • Fiber waviness is one of manufacturing defects encountered frequently in thick composite structures. It affects significantly on the behavior as well as strength of thick composites. The effects of fiber waviness on tensile/compressive nonlinear elastic behavior and strength of thick composite with fiber waviness are studied theoretically and experimentally. FEA(Finite Element Analysis) models are proposed to predict tensile/compressive nonlinear behavior and strength of thick composites. In the FEA models, both material and geometric nonlinearities were incorporated into the model using energy density, iterative mapping and incremental method. Also Tsai-Wu criteria was adopted to predict the strength of thick composites with fiber waviness. Tensile and compressive tests were conducted on the specimens with uniform fiber waviness. It was observed that the degree of fiber waviness in composites significantly affected the nonlinear behavior and strength of the composites

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Nondestructive Evaluation of Fiber Waviness in Thick Composites by Ultrasonics (초음파를 이용한 두꺼운 복합재료의 보강섬유 굴곡 평가)

  • 장필성;전흥재
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 1999.11a
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    • pp.258-263
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    • 1999
  • In this study, the numerical and experimental investigations were conducted to understand ultrasonic wave propagation and to evaluate the degree of fiber waviness in thick composites nondestructively. The path, energy and traveling time of insonified wave were predicted by adopting the ray and plane wave theories. In the analysis, the composites were assumed to have continuous fiber with sinusoidal waviness in a matrix and were modeled as stacks of infinitesimally short length off-axis elements with varying fiber orientation along the length direction. From the experiments on the specially fabricated thick composite specimens with various degrees of uniform fiber waviness, the energy distributions of received wave were obtain for the various positions of transmitter. It was observed that the energy of wave was converged to the adjacent peaks of fiber waviness. The location where maximum energy of wave was detected from the experiments showed good agreement with the location obtained from theoretical predictions. Finally, the test procedure was Proposed to evaluate fiber waviness in thick composites by considering the energy of wave and relative distance between transmitter and receiver.

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Effects of Fiber Waviness on Elastic Properties of Composites and New Fabrication Method for Composites with Uniform Fiber Waviness (굴곡진 보강섬유가 복합재료의 기계적 특성에 미치느 영향과 일정한 보강섬유의 굴곡비를 가지는 복합재료의 성형방법에 관한 연구)

  • Jeon, Heung-Jae;Sin, Jae-Yun;Choe, Heung-Seop
    • Journal of the Korean Society for Precision Engineering
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    • v.16 no.9
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    • pp.135-142
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    • 1999
  • A constitutive model was proposed to study the effects of fiber waviness on the elastic properties of unidirectional composite materials. The predictions showed that the degree of fiber waviness significantly affected the elastic properties of composite materials. A special fabrication technique was developed for thic composite materials with various fiber waviness ratios. Tensile, compressive and flexural tests were conducted to obtain the elastic properties of composite materials with fiber waviness experimentally. The experimental result were in good agreement with the predictions.

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Predictions of Nonlinear Behavior and Strength of Thick Composites with Fiber Waviness under Tensile/Compressive Load (굴곡진 보강섬유를 가진 두꺼운 복합재료의 인장/압축 비선형 거동 및 강도예측)

  • 유근수;전흥재
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2001.04a
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    • pp.819-822
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    • 2001
  • Fiber waviness is one of manufacturing defects encountered frequently in thick composite structures. It affects significantly on the behavior as well as strength of thick composites. Thick composites with fiber waviness have two kinds of nonliearity. One is material nonlinearity, and the other is geometrical nonliearity due to fiber waviness. There are only a few studies that have considered both material and geometrical nonlinearities. In this paper, a FEA model was proposed to predict nonlinear behavior and strength of thick composites with fiber waviness.

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New Constitutive Models for Tensile/Compressive Nonlinear Elastic Behaviors of Composite Materials with Fiber Waviness (굴곡진 보강섬유를 가진 복합재료의 인장/압축 비선형 거동을 예측하기 위한 새로운 해석모델의 개발에 관한 연구)

  • 전홍재;신재윤;최흥섭
    • Composites Research
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    • v.12 no.1
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    • pp.59-67
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    • 1999
  • The effects of fiber waviness on tensile/compressive nonlinear elastic behaviors of graphite/epoxy unidirectional composite materials are studied theoretically and experimentally. New constitutive models are proposed to predict elastic properties and tensile/compressive nonlinear behaviors of composite materials. Three types of wavy pattern are considered: uniform, graded and localized fiber waviness. Complementary energy density and incremental method are used to incorporate the material and geometrical nonlinearities due to fiber waviness. Tensile/compressive tests are conducted on the specimens with fiber waviness. It is found that the predictions are in good agreement with the experimental results.

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Stress and Strain Analyses of Thick Composites with Fiber Waviness under Flexural Loading (굽힘 하중 하에서 굴곡진 보강섬유를 가진 두꺼운 복합재료 보의 응력 분포 해석)

  • 이승우;전흥재
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 1999.11a
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    • pp.95-100
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    • 1999
  • A FEA(finite element analysis model) was proposed to study stress and strain distributions in thick composites with fiber waviness and initial curvature under flexural loading. Three types of model with initial curvature were considered in this study: flat, concave and concave models. In the analysis, both material and geometrical nonlinearities were incorporated. Four point flexural tests were conducted on the flat specimens to obtain the flexural behavior of thick composites experimentally. It was concluded that the predictions from the models were in good agreement with the experimental results. It was shown that the stress and strain distributions as well as nonlinear flexural behaviors of thick composites were significantly affected by the fiber waviness and initial curvature.

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Nonlinear Elastic Analysis of Thick Composites with Fiber Waviness Using a FEA Model (FEA 모델을 이용한 굴곡진 보강섬유를 가진 두꺼운 복합재료의 비선셩 거동에 관한 연구)

  • 이승우;전흥재
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 1999.04a
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    • pp.43-47
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    • 1999
  • A FEA model is proposed to study the effects of fiber waviness on tensile/comprssive nonlinear behaviors of thick unidirectional composites. In the analyses both material and geometical nonlinarities are considered. The predicted results from the FEA model are compared with those obtained from the previous analytical model (thin carpet model) Tensile/compressive tests are also conducted on the specimens with various controlled fiber waviness to obtain the nonlinear behaviors of composites experimentally. The predictions from the FEA model show better agreements with the experiments than those from the analytical model.

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Ultrasound Wave Propagation in Thick Composites with Uniform Fiber Waviness (일정한 보강섬유 굴곡이 있는 두꺼운 복합재료에서의 초음파 전파에 관한 연구)

  • Chun, Heoung-Jae;Jang, Pil-Sung
    • Journal of the Korean Society for Nondestructive Testing
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    • v.21 no.3
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    • pp.288-298
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    • 2001
  • There has been a growing interest in thick composite materials especially for primary structures. Fiber waviness is one of the manufacturing defects frequently encountered in thick composite structures and affects the mechanical properties such as stiffness and strength significantly. Therefore, nondestructive evaluation technique that can detect fiber waviness of thick composite is very important for the integrity of structures. In this study, efforts were made to understand ultrasonic wave propagation in thick composites with uniform fiber waviness by adopting the ray and plane wave theories. Both theoretical and experimental investigations were conducted to understand the wave propagation in thick composites with uniform fiber waviness. The experiments were conducted on specially fabricated thick composite specimens with various degrees of uniform fiber waviness using the conventional through-transmission method to verify the predicted results. The experimental results showed good agreement with the theoretical predictions.

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Prediction of Equivalent Elastic Modulus for Flexible Textile Composites according to Waviness Ratio of Fiber Tows (섬유다발의 굴곡도에 따른 유연직물복합재료의 등가탄성계수 예측)

  • Suh, Young-W.;Kim, Sung-Joon;Ahn, Seok-Min
    • Aerospace Engineering and Technology
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    • v.9 no.2
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    • pp.73-79
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    • 2010
  • In this study, the equivalent elastic modulus of flexible textile composites was predicted by nonlinear finite element analysis. The analysis was carried out considering the material nonlinearity of fiber tows and the geometrical nonlinearity during large deformation using commercial analysis software, ABAQUS. To account for the geometrical nonlinearity due to the large shear deformation of fiber tows, a user defined material algorithm was developed and inserted in ABAQUS. In results, nonlinear stress-strain curve for the flexible textile composites under uni-axial tension was predicted from which effective elastic modulus was obtained and compared to the test result. The effective elastic moduli were calculated for the various finite element models with different waviness ratio of fiber tow.