Page 37 - Fiber Fracture

22 K.K. Chawla

Tuble 1. Effect of BN coating thickness on the mean strength of Nextel 480 fiber (Chawla et al., 1997)
Coating thickness Weibull mean strength
(wm) (GW
0 1.63
0.1 2.00
0.2 2.47
0.3 1.82
1 .0 I .27

or even a very minor chemical heterogeneity. Thus, it is very important to reduce the
number and the size of defects during processing. Similar examples of fracture in E-glass
fiber caused by a dust particle or a metallic inclusion in the near-surface region of the
fiber, most likely formed during processing, can be found in the literature (Chandan et
al., 1994).
In order to meet the increasing demand for bandwidth, dense wavelength division
multiplexing (DWDM) system designers must significantly increase the number of
channels and decrease channel spacing. This has resulted in ever-stringent demands
on the components that make up the telecommunications systems. For example, it is

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Fig. 16. Fracture surface of a Nicalon fiber tested in tension at room temperature (courtesy of N. Chawla).
Arrow indicates the site of initiation of fracture at the fiber surface. The fracture surface shows a planar
mirror 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, or even a very minor chemical heterogeneity.