Page 188 - 3D Fibre Reinforced Polymer Composites

Stitched Composites 177
stitch bridging zone, and the stitches apply bridging tractions to the delamination and
thereby impede crack growth. The bridging zone can extend a long way behind the
crack tip, usually several tens of millimeters or more, and is highly effective in slowing
the rate of crack growth and thereby increasing the interlaminar shear strength. The
bridging mechanism for increasing the interlaminar strength of composites is described
in more detail in Section 8.4.

-
60
h
Carbodepoxy
h -
3 551 I 0
v
5
cn
2 40-
5
% 30-
a,
&
2 20- Kevladepoxy
.-
c
w
f - 1
- 10-
ij
-
c
c
"0 2 4 6 8 10
Stitch Density (ern-*)
Figure 8.9 Effect of stitch density on the apparent interlaminar shear strength, 2, of
Kevlar/epoxy and carbodepoxy composites (data for the Kevladepoxy and
carbodepoxy is from Cholarkara et al. (1989) and Jain and Mai (1997) respectively).

1.4-

5 1.2-
c
(5).
al
b 1.0-
(0
5
0.8
(0.
U
2 0.6
.- - .
m CFRP I180 d Kevlar (Jain B Mai, 1997)
0.4 - I3 CFRP1270 d Kevlar (Jain B Mai.1997)
0
z . 0 CFRP I unspecified denier Kevlar (Ou et at.. 1986)
-
o.2 0 GFRP I315 d Kevlar (Adanur and Tsao, 1994)
A KFRP / unspecified denier Kevlar (Cholarkara et al., 1989)
. A GFRP I 180 d Kevlar (Mouritr el al., 1996) ' '
'
.
'
0.0 I .
Stitch Density (rnrn-')
Figure 8.10 Plot of normalised interlaminar shear strength (T/T,J against stitch density.
The denier and material used for the stitching are as given (Mouritz and Cox, 2000).