Page 212 - 3D Fibre Reinforced Polymer Composites

Stitched Composites 20 1

60
E
E
- 50
6 Unstitched GRP
I"
s 40 Heavily Stitched
I-
30
z
s
2 20
10
5
w o
LOW INTENSITY BLAST HIGH INTENSITY BLAST
(a)

0 Unstitched GRP
Lightly Stitched GRP
Heavily Stitched GRP
T T
300

E 200
u)
-I
X
W
-J
LI
0
NO BLAST LOW INTENSITYHIGH INTENSITY
DAMAGE BLAST
Figure 8.35 (a) Amount of delamination damage caused by a low and high intensity
explosive blast. (b) Flexure-after-blast strengths of stitched and unstitched composites
(Mouritz, 2001).

8.6 STITCHED COMPOSITE JOINTS

For adhesively bonded composite lap joints, typical failure initiates and propagates, in a
form of delamination, along the interface between the surface and the second ply in one
composite adherend. Figure 8.36 schematically depicts the onset and propagation of
interlaminar delamination between the surface and second plies in a double-lap
composite joint. It is believed that the high positive normal stress near an overlap end
and the low interlaminar strength are believed to be the two major contributing factors.
Depending on the joint configuration and loading conditions, a delamination can
propagate along an interface or kink into an adjacent interface, or a sectional fracture
occurs in the deformed surface ply.