FAILURE MECHANISMS
a) b)
Figure 4-6. Stress-strain curves for plain woven carbon/eopxy laminate. (a)
Unnotched. (b) Notched (d = 4 mm). (From [4.24].)
The rest of this section will be directed mainly to failure mechanisms under loads
aligned with a primary set of tows. This is the configuration of most interest for
applications such as airframes where stiffness and strength are paramount.
4.3.1 2D Weaves and Braids
In 2D woven laminates, including plain weaves, satin weaves, etc., the earliest
softening under aligned loads is caused by microcracking within transversely oriented
tows, around tows of both orientations, and between plies. The systems of microcracks are
often complex [4.14], linked to irregularities in geometry, and difficult to correlate with
estimates of local stresses (see Sect. 5). Plastic tow straightening is inhibited by the
interlacing of tows.
