Effects of through-thickness stitching on Mode II delamination toughne
ss (G(IIc)) of graphite/epoxy uniweave textile laminates have been inv
estigated by performing end-notched flerure tests. Different stitch ya
ms and stitch densities were considered. The crack propagation in stit
ched laminates was observed to be gradual and steady, unlike in the un
stitched laminates where it was sudden. New methods of evaluating the
effective or apparent critical strain-energy release rate for stitched
laminates are presented. Stitching results in an excellent improvemen
t in G(IIc) The apparent G(IIc) was 5 to 15 times that of the unstitch
ed laminates, depending on the stitching parameters. There appears to
be an optimum stitch density at which the toughness will be a maximum.
The critical strain-energy release rate increases with increase in cr
ack length as more and more stitches bridge the delamination. (C) 1997
Elsevier Science Limited.