A review of inorganic fibers other than asbestos, glass, and carbon fibers and optical and hollow fibers. Special emphasis is placed on high-performance fibers. The manufacture, structure, properties, and uses of the selected fibers are discussed.

Inorganic Fibers—A Literature Review

Promise and challenges of SiCf/SiC composites for fusion energy applications

The transverse thermal conductivity of 2D-SiCf/SiC composites

Advanced thermal protection materials envisioned for use on future hypersonic vehicles will likely be subjected to temperatures in excess of 1811 K (2800 F) and, therefore, will require the rapid conduction of heat away from the stagnation regions of wing leading edges, the nose cap area, and from engine inlet and exhaust areas. Carbon-carbon composite materials are candidates for use in advanced thermal protection systems. For design purposes, high temperature thermophysical property data are required, but a search of the literature found little thermal conductivity data for carbon-carbon materials above 1255 K (1800 F). Because a need was recognized for in-plane and through-the-thickness thermal conductivity data for carbon-carbon composite materials over a wide temperature range, Langley Research Center (LaRC) embarked on an effort to compile a consistent set of thermal conductivity values from room temperature to 1922 K (3000 F) for carbon-carbon composite materials on hand at LaRC for which the precursor materials and thermal processing history were known. This report documents the thermal conductivity data generated for these materials. In-plane thermal conductivity values range from 10 to 233 W/m-K, whereas through-the-thickness values range from 2 to 21 W/m-K.

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Thermal Conductivity Database of Various Structural Carbon-Carbon Composite Materials

The interlaminar shear strengths of three ceramic matrix composites have been characterized using a double-notch shear (DNS) test. The material systems investigated are plain woven C/SiC, plain woven SiC/SiC, and cross-plied SiC/calcium aluminosilicate-II. The use of the double-notch shear test for measuring the interlaminar shear strength of ceramic matrix composites is evaluated first. Numerical stress analyses are performed to investigate the effect of DNS specimen length, notch distance, and specimen supporting jig on the stress distribution in the expected fracture plane and the interlaminar shear strength. The numerical findings are then compared with an analytical model proposed elsewhere and correlated with the experimental results. The validity of this test technique has been established.

Characterization of Interlaminar Shear Strength of Ceramic Matrix Composites

The thermal diffusivity of chemically vapour deposited silicon carbide reinforced with either Nicalon SiC yarn or PAN-precursor carbon fibres was measured by the laser-flash method during various time-temperature treatments. The diffusivity was found to depend on the degree of densification, the direction of heat flow with respect to the fibre orientation, and the thermal history. Structural modifications, confirmed by X-ray diffraction, produced large permanent changes in the thermal properties of the SiC-SiC composites when heated above 1200° C, while only minor changes were seen in C-SiC composites heated above 1500° C.

Thermal diffusivity of chemically vapour deposited silicon carbide reinforced with silicon carbide or carbon fibres

A model study was conducted of the thermal fatigue and single-cycle thermal shock resistance of indented soda-lime-glass rods heated over durations sufficiently short that thermal equilibrium was not reached prior to quenching into a water bath. The experimental results indicate that for short heating periods thermal fatigue life at fixed ΔT and the critical quenching temperature difference (Δ7c) for a single-cycle quench significantly exceed the corresponding values obtained for specimens heated for sufficiently long periods that conditions of final thermal equilibrium were obtained prior to quenching. The implications of these results for single-cycle and multicycle thermal shock testing are discussed.

Effect of heating time on the thermal stress resistance of a soda-lime-silica glass

Indentation fracture studies were conducted on three sodium borosilicate glasses containing a dispersed phase of alumina inclusions with different degrees of thermal expansion mismatch between the glass matrices and the alumina. The alumina inclusions were found to cause a significant decrease in the size of the indentation cracks compared to those in the glass. This effect was greatest at the higher values of indentation load, which resulted in cracks of dimensions of sufficient size that their propagation was impeded by the tougher alumina dispersions. The fracture toughness for the composite samples calculated from the indentation data showed a significant increase with increasing crack size. For the smallest cracks in these composites, the value for fracture toughness was well below the value obtained in an earlier study by the single-edge notch-beam technique. The fracture toughness for the larger crack sizes which interacted with the alumina dispersions showed excellent agreement with the notch-beam data. The residual stresses due to the thermal expansion mismatch appeared to lead to a slight increase in the mean crack size regardless of the direction of thermal expansion mismatch.

Henri Tawil

Papers

Thermal diffusivity of chemically vapour deposited silicon carbide reinforced with silicon carbide or carbon fibres

Effect of heating time on the thermal stress resistance of a soda-lime-silica glass

Effect of inclusions on size of surface flaws in glass-crystal composites