ANALYTICAL METHODS FOR TEXTILE COMPOSITES
θ
2h
h
t
(a) mid-plane delamination
(b) surface delamination
angle interlock
weave
stitched
laminate
SC.3066T.110395
θ
Figure 4-4. Schematic of buckling under in-plane compression following
delamination due to impact.
2D Weaves and Braids
Under aligned compression, 2D weaves and braids without prior damage typically
fail by a combination of shear plasticity and delamination [4.2,4.12]. Shear failures may
appear as kink bands, although the evidence for kinking is often obscured by the extent of
damage that immediately ensues tow failure. Nevertheless, clear evidence exists for kinking
in plain and satin weaves [4.12-4.14] and in nominally straight axial tows in triaxial braids
[4.2,4.15]. Large scale delaminations occur between plies [4.12]. Localized delaminations
may occur between tows within the same ply, especially along the float in 2D weaves (Fig.
4-5).
Representative compression strength data for four carbon/epoxy triaxial braids are
shown in Table 4.1 [4.16]. The braid with a low percentage of axial yarns,
{[0
6k
/±45
15k
]12% Axial}, failed by extensive shear cracking in the bias rovings with a
very nonlinear stress-strain curve similar to Fig. 4-2 (see also similar data in
[4.2,4.14,4.17]). The strength of the remaining, axially dominated braids was controlled
by splitting and buckling of the axial fiber bundles, which presumably involved kink bands
like those reported in [4.2,4.14,4.15]; and the stress-strain curves were nearly linear to
failure.
