Fiber orientations were measured through the thickness as shown
in Fig. 1, which indicates that the three samples had nominal fiber orientations
of 30, 45, and 75 degrees with some variability between layers.
Fiber Orientation
Dow Corning prepared three sets of special specimens all of Nicalon fiber in a 2-dimensional layup using an 8-harness satin weave. All were infiltrated with Dow Corning's proprietary pyrolysis process.
The work employed new nondestructive characterization technologies that have in part been developed under the CFCC program.
To measure the 2-dimensional fiber orientations through the thickness of the 4 mm-thick specimens, high spatial resolution X-ray computed tomography and advanced image processing methods were used. The specimens were provided to the researchers without knowledge of the fiber orientations.
Fiber orientations were measured through the thickness as shown
in Fig. 1, which indicates that the three samples had nominal fiber orientations
of 30, 45, and 75 degrees with some variability between layers.
Density
To measure densities, the researchers again employed X-ray technology but this time employed digital radiography methods using the same X-ray machine as is used for computed tomography but without producing cross-sectional images.
Dow Corning made four special specimens with different densities ranging from 1.92 to 2.17 g/cc. By measuring the X-ray attenuation, Argonne was able to clearly establish a correlation between measured attenuation and density.
Fiber-Matrix Interface
To establish sensitivity to fiber-matrix interface coatings, Argonne selected another NDC modality, infrared imaging, and special computer analysis of the resulting image data using software written by Argonne.
A thermal flash method was used to acquire data in a manner similar to commercial systems used to make thermal diffusivity measurements. The advantage of the Argonne system is that both large and small components can be examined.
The system was calibrated using specimens from the National Institute of Standards and Technology. Dow Corning produced a special set of three specimens with different coatings to see if the thermal method could sense differences between the specimens with coatings of known differences in thermal properties.
The composite without a fiber coating had a thermal diffusivity of 0.89x10(-6)m(2)/s. The composite thermal diffusivity increased to 0.91x10(-6)m(2)/s when a 2mm thick fiber coating of pyrolytic carbon was added. A proprietary fiber coating reduced the composite thermal diffusivity to 0.81x10(-6)m(2)/s.
Argonne is exploring other advanced nondestructive characterization methods to learn more about CFCC materials systems both for their role in process development and lifetime prediction models. These include detection of thermal shock damage, delaminations, pore distribution, and fiber distribution.
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Comments to: mgc@ornl.gov
Revised: July 5, 1995