Page 180 - Fiber Fracture

FRACTURE OF CARBON FIBERS 165

fibre axis
Fig. 10. Model of microtexture of PAN-based carbon fiber. (Copyright 1984, reproduced with permission
from Elsevier Science.)

The weight loss experienced in the production of carbon fibers from PAN precursor is
approximately 50%. Guigon et al. (1984) showed that this leads to a structure containing
many longitudinal voids, as shown in Fig. 10, and a density of -1.8 g/cm3, compared
with 2.28 g/cm3 for pure graphite, and 2.1 for pitch-based carbon fibers. Boyes and
Lavin (1998) showed evidence for the polymeric nature of the fiber in the fracture
surface shown in Fig. 1 1. The fibrils are evident on the wall of the fiber. An enlargement
of the fracture surface in Fig. 12 shows fibrils at the nanometer scale. The results of
a remarkable experiment by Kwizera et al. (1982) are shown in Fig. 13. A Celion
GY-70 fiber was fractured in vacuum, and exploded into microfibrils roughly 100 nm in
diameter, further confirming the fibrillar nature of the PAN-based fiber.