Thermal conductivity and thermal expansion of graphite fiber/copper matrix composites
The high specific conductivity of graphite fiber/copper matrix (Gr/Cu) composites offers great potential for high heat flux structures operating at elevated temperatures. To determine the feasibility of applying Gr/Cu composites to high heat flux structures, composite plates were fabricated using unidirectional and cross-plied pitch-based P100 graphite fibers in a pure copper matrix. Thermal conductivity of the composites was measured from room temperature to 1073 K, and thermal expansion was measured from room temperature to 1050 K. The longitudinal thermal conductivity, parallel to the fiber direction, was comparable to pure copper. The transverse thermal conductivity, normal to the fiber direction, was less than that of pure copper and decreased with increasing fiber content. The longitudinal thermal expansion decreased with increasing fiber content. The transverse thermal expansion was greater than pure copper and nearly independent of fiber content.
Numerization of a memory effect for an homogenized composite material with a large contrast in the phase thermal conductivities
Abstract In this article, we propose a systematic numerical solution method for deriving the homogenized material parameters in the case where a large contrast in the phase thermal properties leads to a macroscopic memory effect. Focus is therefore set on the determination of this memory effect for a periodic microstructure. As for other and more classical homogenized parameters, the possibility of analyzing with the finite element method a single periodic cell is used, and a transient simulation allows to provide the incremental evolution of the memory effect function. Additionally, some approximations are proposed for a low cost estimate of this function, and validated on two examples.
Progress in the Development of Graphite- Aluminum Composites Using Liquid Infiltration Technology
The most successful techniques for producing graphite-aluminum com posites have been those that utilize liquid-metal infiltration of graphite yarn. Almost all grades and types of graphite yarn can be infiltrated; how ever, a fiber coating is required, which results in wetting and provides a diffusion barrier to inhibit aluminum carbide formation. Two fiber coating methods are discussed in detail, including the sodium pretreatment method that results in intermetallic compound formation on the fiber and a chem ical vapor deposition method that applies a titanium-boron codeposit.