Bounds on the Transverse Effective Conductivity of Computer-Generated Fiber Composites

1982 ◽  
Vol 49 (2) ◽  
pp. 319-326 ◽  
Author(s):  
J. J. McCoy
Keyword(s):  
Thermal Conductivity ◽  
Effective Conductivity ◽  
Fiber Composite ◽  
Effective Property ◽  
Fiber Composites ◽  
Area Fraction ◽  
Fiber Area ◽  
Single Body ◽  
Transverse Thermal Conductivity ◽  
Dilute Suspension

Using trial functions that are motivated by single-body calculations, we have derived bounds on the effective transverse thermal conductivity of a fiber composite. These bounds incorporate both fiber area fraction information and some information of the configurational statistics. Simplified expressions for the bounds are obtained for the limits of widely differing conductivity values for the constitutent phases, and of a dilute suspension. The bounds are made specific for a given computer-generated fiber composite and these specific bounds are compared with the best available bounds that require area fraction information alone. The conclusions reached are that configuration statistics are significant for effective property calculations for moderately dense composites for component conductivity values that differ by some one to two orders of magnitude, or greater. Further, the bounds based on the single-body calculation are reasonably close for component conductivity values that differ by some two orders of magnitude, or less.

Thermal and Electrical Conductivities of Porous Carbon-Coated Ceramic Fiber Composites

2006 ◽  
Vol 317-318 ◽  
pp. 491-494 ◽  
Author(s):  
Jae Chun Lee ◽  
Jun Suh Yu ◽  
Jae Hoon Sung ◽  
Sung Park ◽  
Sung Chul Choi
Keyword(s):  
Thermal Conductivity ◽  
Electrical Conductivity ◽  
Effective Conductivity ◽  
Porous Ceramic ◽  
Pyrolytic Carbon ◽  
Fiber Composites ◽  
Nitrogen Atmosphere ◽  
Ceramic Fiber ◽  
Electrical Conductivities ◽  
Carbon Coated

Porous ceramic fiber composites were coated with pyrolytic carbon by the decomposition of infiltrated phenolic resin in a nitrogen atmosphere at 800. The amount of carbon coating was varied to tailor the electrical conductivity of the carbon-coated composites. The electrical and thermal conductivity of the composites were measured at room temperature using a two-point method and a hot-wire one, respectively. Up to 30 wt% pyrolytic carbon, the electrical conductivity σ shows linearly increasing tendency and is fitted by the effective conductivity according to the parallel rule of a mixture σeff = ΣΧi ·σi with an effective conductivity of pyrolytic carbon σc= 0.42 S/cm. The thermal conductivity of the coated composites is in the range 0.05-0.08 W/mK and increases with carbon content.

Electrical and Thermal Properties of Carbon-Coated Porous Ceramic Fiber Composites

2005 ◽  
Vol 486-487 ◽  
pp. 370-373
Author(s):  
Jun Suh Yu ◽  
Sung Park ◽  
Jae Chun Lee ◽  
In Sup Hahn ◽  
Sang Kuk Woo
Keyword(s):  
Thermal Conductivity ◽  
Electrical Conductivity ◽  
Carbon Coating ◽  
Effective Conductivity ◽  
Porous Ceramic ◽  
Pyrolytic Carbon ◽  
Fiber Composites ◽  
Nitrogen Atmosphere ◽  
Ceramic Fiber ◽  
Carbon Coated

Porous ceramic fiber composites were coated with pyrolytic carbon by the decomposition of propane in a nitrogen atmosphere at 900°C. The amount of carbon coating was varied through adjusting deposition time to tailor the electrical conductivity of the carbon-coated composites. The electrical and thermal conductivity of the composites were measured at room temperature using a two-point method and a hot-wire method, respectively. Up to 7 wt% pyrolytic carbon, the electrical conductivity σ is linearly increased to 0.02 S/cm and well fitted by the effective conductivity according to the parallel rule of a mixture σ eff = Σ Χ i ·σ i with a conductivity of pyrolytic carbon σ c= 20 S/cm .The thermal conductivity of the uncoated and coated composites is in the range 0.065-0.075 W/mK and little affected by carbon coating presumably owing to the small amount of coated carbon in this work.

Effective Thermal Conductivity of Ordered Short-Fiber Composites With Single-Fiber Uniform Hexagonal Prism Cell

2012 ◽  
Author(s):  
Marcelo B. Martinez ◽  
Manuel E. Cruz ◽  
Carlos F. Matt
Keyword(s):  
Finite Element ◽  
Effective Properties ◽  
Effective Conductivity ◽  
Numerical Study ◽  
Fiber Composite ◽  
Fiber Composites ◽  
Short Fiber ◽  
Single Fiber ◽  
Hexagonal Prism ◽  
Element Discretization

The bulk behavior of short-fiber composite materials in mechanical, thermal, and electrical applications is of great engineering interest. The reliability of analytical and numerical studies dedicated to these topics depends to a large extent on the postulated, or prescribed, microstructure configurations. Of course, different spatial distributions of fibers lead to different configurations, which in turn influence the effective properties. There are no established (or benchmarked) microstructure configurations (or models) to be used in investigations aimed at calculating the macroscopic behavior of classes of real composite material bodies. In the present numerical study of heat conduction in composites, accurate results for the longitudinal and transverse effective thermal conductivities of short-fiber composites with single-fiber uniform hexagonal prism cell are calculated and validated. The three-dimensional periodic cell microstructure consists of one short circular cylindrical fiber placed at the center, and perpendicular to the two parallel regular hexagons, of the prism. Previous continuous formulation and computational implementation are employed, based on the method of homogenization and finite element discretization. A procedure for generating the domain of the uniform hexagonal prism cell, and the respective tetrahedral finite-element mesh, has been realized using a third-party software. The numerical effective conductivity results obtained in the 3-D calculations are validated against analytical results for the 2-D hexagonal array of circular cylinders.

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