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290 Fracture Mechanics: Fundamentals and Applications

FIGURE 6.37 Stress-strain behavior of fiber-reinforced ceramic composites.

the load is carried by the fibers. The fibers do not fail simultaneously, because the fiber strength
is subject to statistical variability [46]. Consequently, the material exhibits quasi ductility, where
damage accumulates gradually until final failure.
Not only is fiber bridging the most effective toughening mechanism for ceramics (Table 6.1),
it is also effective at high temperatures [47, 48]. Consequently applications that require load-bearing
capability at temperatures above 1000°C will undoubtedly utilize fiber-reinforced ceramics.
Whisker-reinforced ceramics possess reasonably high toughness, although whisker reinforcement
is not as effective as continuous fibers. The primary failure mechanism in whisker composites appears
to be bridging [49]; crack deflection also adds an increment of toughness. Figure 6.38 is a micrograph
that illustrates crack bridging in an Al O ceramic reinforced by SiC whiskers.
2
3

FIGURE 6.38 Crack bridging in Al 2 O 3 reinforced with SiC whiskers. Photograph provided by A.G. Evans.
Taken from Evans, A.G., “The New High Toughness Ceramics.” ASTM STP 1020, American Society for
Testing and Materials, Philadelphia, PA, 1989, pp. 267–291.