Page 39 - Fiber Fracture

24 K.K. Chawla

fibers. The use of pulsed excimer radiation for FBG production lowered the Weibull
modulus as well as the fiber fracture strength by as much as a factor of 4 compared to
the fiber that was subjected to a CW argon-ion laser for the FBG production. The lower
fracture strength of pulse-irradiated fiber is a result of the formation of microcracks in
the material.

CONCLUSIONS

Typically, fibers have a high surface area/volume ratio, which leads to fiber surface
characteristics being very important in the fracture process.
By far the major cause of fracture in fibers is the presence of flaws either on the
surface of the fiber or in the interior. If the size of the flaw can be reduced through
processing or safe handling, the strength of the fiber will increase.
A stringent control of microstructural cleanliness and segregation are very important.
This is true for all types of fibers: glass, carbon, metal, polymers, or ceramic,
Fracture surface analysis of fibers can provide useful information. In particular,
for noncrystalline fibers, the following fracture parameters can be obtained from
an analysis of features on the fracture surface morphology: the mirror constant,
an estimation of fracture toughness KI,, failure stress, flaw-to-mirror radius ratio,
fracture surface energy, and the time to failure.

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