The effect of stitching on FRP cylindrical shells under axial compression

FRP composites have usually poor through-thickness mechanical properties and, therefore, are able to sustain more loads in tension than in compression and fail as a consequence of buckling. The through-thickness reinforcement is carried out by stitching to improve the delamination strength and to reduce the in-plane crack growth rate. Experiments were performed on both stitched and unstitched laminated plates which were prepared by using woven roving glass fibre mat and chopped strand glass fibre mat with polyester resin, and the effect of stitching was studied. It is observed that stitching increases delamination strength to a great extent. There are losses in the in-plane mechanical properties due to in-plane fibre damage and creation of resin-rich pockets. Various energy-absorbing modes observed during progressive crushing of both stitched and unstitched FRP cylindrical shells under axial compression were studied both experimentally and theoretically. Analytical expressions for the calculation of energy absorption in various modes and average crush stress were derived, and the results thus obtained were compared with the experiments.