Page 36 - Fiber Fracture

FIBER FRACTURE: AN OVERVIEW 21
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Fig. 15. (a) The rough surface of a polycrystalline alumina fiber. SEM. (b) The grain structure of an alumina
fiber. TEM. Rough surface of such brittle fibers makes them break at very low strain and it makes very
difficult to handle them in practice.

The room temperature fracture surface of a Nicalon fiber is shown in Fig. 16. Note
the initiation of fracture at the fiber surface. The fracture surface shows a crack-initiating
site and a planar minor region, a misty region, and finally a hackle region in which crack
branching occurs. The initiating flaw may be an impurity, a surface nick due to handling,