Page 201 - 3D Fibre Reinforced Polymer Composites

190 30 Fibre Reinforced Polymer Composites

toughness for equivalent stitch densities. Most stitched composites exhibit a GIIR value
that is typically 2 to 6 times higher than the unstitched laminate, depending on the type
and amount of stitching. It was shown earlier that the mode I delamination resistance
can be increased by much more this.

'
-
Continuous Stitching Model
0 Modified Stitching Model
6-

5-

0 1 2 3 4 5 6 7
Measured (& (kJ/d)
Figure 8.24 Plot of measured against theoretical GIR values for stitched composites.
The theoretical GIR values were determined using the modified and continuous stitching
models by Jain and Mai. The closer the data points are to the straight line the better the
agreement between the measured and theoretical GIR value (Adapted from Mouritz and
Jain, 1999).

'D
@J
s o
0 2 4 6 8 1 0 1 2 1 4
Stitch Density
Figure 8.25 The effect of stitch density on the mode I1 interlaminar fracture toughness
of a carbodepoxy composite (Data from Dransfield et al., 1995).