Effect of stitching on the static and fatigue properties of fibre-dominated and matrix-dominated composite laminates

The paper reports the results of an experimental investigation into the effect of stitching on the static and fatigue response of fibre-dominated and matrix-dominated laminates. The tests were conducted on stitched carbon/epoxy laminates with quasi-isotropic ([0/±45/90]s) or angle-ply ([+302/− 302]s, [+452/− 452]s, [+602/− 602]s) layups. The analyses show that stitching significantly reduces both the static and the fatigue strength of fibredominated [0/±45/90]s laminates, owing to the presence of localized fibre damage introduced during the stitching process. On the other hand, stitching does not affect the fatigue response of [+602/− 602]s laminates but significantly improves the fatigue strength of [+302/− 302]s and [+452/− 452]s laminates. The effectiveness of stitching on the fatigue performance of the angle-ply layups was found to be directly related to the specific damage mechanisms preceding the ultimate failure, which are controlled by edge delaminations in [+302/− 302]s and [+452/− 452]s and transverse matrix cracking in [+602/− 602]s laminates.