Characterization and control of the fiber-matrix interface in ceramic ...

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9.4 Mechanical ProDerties
9.4.1 Sample vreoaration
The densified composites were weighed in the graphite holders to
examine densification. In some earlier experiments, the seals at the
injector leaked, resulting in incomplete infiltration. Fortunately,
this did not occur in this series; thus, samples were not returned to
the furnace for further densification. All infiltration runs were
completed in one step. The composite samples were then removed from
their holders by cutting and grinding away the graphite using carbidetipped
tool bits"
The samples were then sliced into various pieces for analysis.
Figure 9.6 shows the areas from which the specimens were removed. All
cutting and grinding was accomplished using a high-speed grinder/slicer.
Metal-bonded low-concentration slicing blades were employed in the
cutting, and low-concentration resin-bonded wheels were used for
grinding.
9.4.2 Flexure testing
Twelve bend bars were prepared from each sample (four each from the
top, middle, and bottom areas) to determine variations within and between
samples (Figure 9.6). The bars were cut from the samples parallel to
the 0-90" orientation of the top layer of cloth using a diamond saw,
and tensile and compression surfaces were ground parallel to the long
axis of the specimens. The average dimensions of the bars were
2.5 x 3.3 x 45 mm; all were measured and weighed to determine densities.
The strengths of all composites were measured in four-point bending.
It has been noted that the four-point flexure test does not measure the