Page 192 - Fiber Fracture

FRACTURE OF CARBON FIBERS 177

fibers are seldom subjected to large compressive forces. These tests are typically either
knot tests or recoil tests, and PAN-based fibers typically fail in either micro-buckling
or shear, while mesophase pitch-based fibers fail in shear at a much lower level. These
failure modes are illustrated in Figs. 25 and 26.
In composites, Drzal and Madhukar (1993) observed that the failure mode depended
on the level of fiber/matrix adhesion: at low levels, the mechanism was global
delamination buckling; at intermediate levels, fiber microbuckling; at high levels fiber
compressive (shear) failure. This is illustrated in Fig. 27.

Fig. 26. Kink bands in PAN-based carbon fibers after recoil compression under high deformation. From
Dobb et al. (1990). (Copyright 1990, reprinted with permission from Kluwer Academic Press.)

Fig. 27. Major failure modes for carbon fiber/epoxy laminates. From Drzal and Madhukar (1993).
(Copyright 1993, reprinted with permission from Kluwer Academic Press.)