• Title/Summary/Keyword: Unidirectional interface

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Boundary element analysis of singular thermal stresses in a unidirectional laminate

  • Lee, Sang Soon;Kim, Beom Shig
    • Structural Engineering and Mechanics
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    • v.5 no.6
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    • pp.705-713
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    • 1997
  • The residual thermal stresses at the interface corner between the elastic fiber and the viscoelastic matrix of a two-dimensional unidirectional laminate due to cooling from cure temperature down to room temperature were studied. The matrix material was assumed to be thermorheologically simple. The time-domain boundary element method was employed to investigate the nature of stresses on the interface. Numerical results show that very large stress gradients are present at the interface corner and this stress singularity might lead to local yielding or fiber-matrix debonding.

Viscoelastic Analysis of Stress Intensity Factor for Interface Edge Crack in a Unidirectional Liminate (단일방향 복합재료의 공유면에 존재하는 계면 모서리균열의 점탄성 해석)

  • 이상순;김범식
    • Computational Structural Engineering
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    • v.10 no.1
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    • pp.129-134
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    • 1997
  • Interfacial stress singularity in a unidirectional two-dimensional laminate model consisting of an elastic fiber and a viscoelastic matrix has been investigated using the time-domain boundary element method. First, the interfacial singular stresses between the fiber and the matrix of a unidirectional laminate subjected to a uniform transverse tensile strain have been investigated near the free surface, but without any defect or any edge crack. Such a stress singularity might lead to fiber-matrix debonding or interfacial edge cracks. Then, the overall stress intensity factor for the case of a small interfacial edge crack of length a has been computed.

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Elastic-Plastic Stress Distributions Behavior in the Interface of SiC/Ti-15-3 MMC under Transverse Loading(I) (횡하중을 받는 SiC/Ti-15-3 MMC 복합재 계면영역에서의 탄소성 응력장분포거동(I))

  • Kang Ji-Woong;Kim Sang-Tae;Kwon Oh-Heon
    • Journal of the Korean Society of Safety
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    • v.19 no.4 s.68
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    • pp.25-30
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    • 2004
  • Unidirectional fiber-metal matrix composites have superior mechanical properties along the longitudinal direction. However, the applicability of continuous fiber reinforced MMCs is somewhat limited due to their relatively poor transverse properties. Therefore, the transverse properties of MMCs are significantly influenced by the properties of the fiber/matrix interface. In this study, the interfacial stress states of transversely loaded unidirectional fiber reinforced metal matrix composites investigated by using elastic-plastic finite element analysis. Different fiber volume fractions $(5-60\%)$ were studied numerically. The interface was treated as thin layer (with different properties) with a finite thickness between the fiber and the matrix. The fiber is modeled as transversely isotropic linear-elastic, and the matrix as isotropic elastic-plastic material. The analyses were based on a two-dimensional generalized plane strain model of a cross-section of an unidirectional composite by the ANSYS finite element analysis code.

Elastic-Plastic Stress Distributions Behavior in the Interface of SiC/Ti-15-3 MMC under Transverse Loading(II) (횡하중을 받는 SiC/Ti-15-3 MMC 복합재 계면영역에서의 탄소성 응력장분포거동(II))

  • Kang Ji-Woong;Kwon Oh-Heon
    • Journal of the Korean Society of Safety
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    • v.20 no.2 s.70
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    • pp.26-31
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    • 2005
  • The strong continuous fiber reinforced metal matrix composites (MMCs) are recently used in aerospace and transportation applications as an advanced material due to its high strength and light weight. Unidirectional fiber-metal matrix composites have superior mechanical properties along the longitudinal direction. However, the applicability of continuous fiber reinforced MMCs is somewhat limited due to their relatively poor transverse properties. Therefore, the transverse properties of MMCs are significantly influenced by the properties of the fiber/matrix interface. In order to be able to utilize these MMCs effectively and with safety, it must be determined their elastic plastic behaviors at the interface. In this study, the interfacial stress states of transversely loaded unidirectional fiber reinforced metal matrix composites investigated by using elastic-plastic finite element analysis. Different fiber volume fractions $(5-60\%)$ were studied numerically. The interlace was treated as three thin layer (with different properties) with a finite thickness between the fiber and the matrix. The fiber is modeled as transversely isotropic linear-elastic, and the matrix as isotropic elastic-plastic material. Using proposed model, the effects of the interface region and fiber arrangement in MMCs on the distributions of stress and strain are evaluated. The stress distributions of a thin multi layer interface have much less changes compared with conventional perfect interface. The analyses were based on a two-dimensional generalized plane strain model of a cross-section of an unidirectional composite by the ANSYS finite element analysis code.

Evaluation of elastic-plastic behavior in MMC interface according to the reinforced fiber placement structure (강화섬유 배치구조에 따른 MMC계면에서의 탄소성거동 평가)

  • Kang, Ji-Woong;Kim, Sang-Tae;Kwon, Oh-Heon
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.410-414
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    • 2004
  • Under longitudinal loading continuous fiber reinforced metal matrix composite(MMC) have interpreted an outstanding performance. However, the applicability of continuous fiber reinforced MMCs is somewhat limited due to their relatively poor transverse properties. Therefore, the transverse properties of MMCs are significantly influenced by the properties of the fiber/matrix interface. In this study, elastic-plastic behavior of transversely loaded unidirectional fiber reinforced metal matrix composites investigated by using elastic-plastic finite element analysis. Different fiber placement(square and hexagon) and fiber volume fractions were studied numerically. The interface was treated as three thin layer (with different properties) with a finite thickness between the fiber and the matrix. The analyses were based on a two-dimensional generalized plane strain model of a cross-section of an unidirectional composite by the ANSYS finite element analysis code.

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Interfacial Strain Distribution of a Unidirectional Composite with Randomly Distributed Fibers (불규칙 섬유배열을 가진 일방향 복합재료의 경계면 변형률 분포 해석)

  • Ha Sung-Kyu;Jin Kyo-Kook;Oh Je-Hoon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.3 s.246
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    • pp.260-268
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    • 2006
  • The micromechanical approach was used to investigate the interfacial strain distributions of a unidirectional composite under transverse loading in which fibers were usually found to be randomly packed. Representative volume elements (RVE) for the analysis were composed of both regular fiber arrays such as a square array and a hexagonal array, and a random fiber array. The finite element analysis was performed to analyze the normal, tangential and shear strains at the interface. Due to the periodic characteristics of the strain distributions at the interface, the Fourier series approximation with proper coefficients was utilized to evaluate the strain distributions at the interface for the regular and random fiber arrays with respect to fiber volume fractions. From the analysis, it was found that the random arrangement of fibers had a significant influence on the strain distribution at the interface, and the strain distribution in the regular fiber arrays was one of special cases of that in the random fiber array.

Mechanical Properties of Unidirectional Carbon-carbon Composites as a Function of Fiber Volume Content

  • Dhakate, S.R.;Mathur, R.B.;Dham, T.L.
    • Carbon letters
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    • v.3 no.3
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    • pp.127-132
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    • 2002
  • Unidirectional polymer composites were prepared using high-strength carbon fibers as reinforcement and phenolic resin as matrix precursor with keeping fiber volume fraction at 30, 40, 50 and 60% respectively. These composites were carbonized at $1000^{\circ}C$ and graphitised at $2600^{\circ}C$ in the inert atmosphere. The carbonized and graphitised composites were characterized for mechanical properties as well as microstructure. Microscopic studies were carried out of the polished surface of carbonized and graphitised composites after etching by chromic acid, to understand the effect of fiber volume fraction on oxidation at fiber-matrix interface. It is found that the flexural strength in polymer composites increases with fiber volume fraction and so does for the carbonised composites. However, the trend was found to be reversed in graphitised composites. In all the carbonized composites anisotropic region has been observed at fiber-matrix interface which transforms into columnar type microstructure upon graphitisation. The extension of strong and weak columnar type microstructure is function of fiber volume fraction. SEM microscopy of the etched surface of the sample reveal that composites containing 40% fiber volume has minimum oxidation at the interface, revealing a strong interfacial bonding.

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Boundary Element Analysis of Stress Intensity Factor for Interface Edge Crack in A Unidirectional Composite (단일방향 복합재료의 공유면에 존재하는 모서리 균열의 경계요소해석)

  • 이상순;김정규
    • Computational Structural Engineering
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    • v.9 no.1
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    • pp.77-83
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    • 1996
  • The overall stress intensity factor for edge crack located at the interface between fiber and matrix of a unidirectional graphite/epoxy laminate model subjected to a transverse tensile strain have been computed using the boundary element method. Such crack might be generated due to a stress singularity in the vicinity of the free surface. The amplitude of complex stress intensity factor has the constant value at large crack lengths.

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Unidirectional Solidification of $Al-CuAl_2$ Eutectic Composites under Forced Convection by Vibration (진동하에서 일방향응고 시킨 $Al-CuAl_2$ 공정복합재료의 응고에 관한 연구)

  • Lee, Hyun-Kyu;Lee, Kil-Hong
    • Journal of Korea Foundry Society
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    • v.18 no.3
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    • pp.234-239
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    • 1998
  • Unidirectional solidification of $Al-CuAl_2$ eutectic composites was studied under the condition of forced convection by vibration. It has been shown that thermal gradient for solid is different from that for liquid during solidification under force convection by vibration. With increase of vibration, mobility of liquid increases, but decreases with decreasing vibration. The rate of solidification is very high initially, and decreases suddenly. For further solidification, the rate of solidification decrceases slowly, and shows a L-type behavior. The mechanical vibration during solidification effects efficiently on nucleation, and induces a forced convection in liquid. By the forced convection, great thermal gradient of liquid interface between solid and liquid can be obtained. The amount of solute near the interface also decreases as solute distribution is improved by the forced convection.

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Microstructure and Mechanical Property Changes of Unidirectional and Plain Woven CF/Mg Composite Laminates after Corrosion (일방향 및 평직 CF/Mg 복합재 적층판의 부식에 따른 미세조직 및 기계적 특성 변화)

  • Yim, Shi On;Lee, Jung Moo;Lee, Sang Kwan;Park, Yong Ho;Park, Ik Min
    • Korean Journal of Metals and Materials
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    • v.50 no.9
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    • pp.697-702
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    • 2012
  • In this study, unidirectional and plain woven carbon fiber reinforced magnesium matrix composite laminates were fabricated by the liquid pressing infiltration process, and evolutions of the microstructure and compressive strength of the composite laminates under corrosion were investigated by static immersion tests. In the case of the unidirectional composite laminate, the main microstructural damage during immersion appeared as a form of corrosion induced cracks, which were formed at both CF/Mg interfaces and the interfaces between layers. On the otherhand, wrap/fill interface cracks were mainly formed in the plain woven composite laminate, without any cracks at the CF/Mg interface. The formation of these cracks was considered to be associated with internal thermal residual stress, which was generated during cooling after the fabrication process of these materials. As a consequence of the corrosion induced cracks, the thickness of both laminates increased in directions vertical to the fibers with increasing immersion time. With increasing immersion time, the compressive strengths of both composite laminates also decreased continuously. It was found that the plain woven composite laminates have superior corrosion resistance and stability under a corrosive condition than unidirectional laminates.