Damage tolerance and durability of selectively stitched stiffened composite structures

Through-the-thickness stitching is one of the promising approaches to improve the impact damage tolerance of stiffened composite structures. In this research, the effect of selective stitching on impact damage tolerance and fatigue durability of stiffened composite panels was extensively investigated and compared with unstitched stiffened composite panels. Two-blade stiffened composite panels were fabricated by resin film infiltration technique. Impact damage was inflicted on the stiffened panels using a drop-weight with the impact energy of 30 J from the skin-side over the stiffener and the flange. The experimental results indicate that selective stitching is an effective way to improve the compressive failure strength and fatigue strength of stiffened panels with both clearly visible flange damage (CVFD) and clearly visible stiffener damage (CVSD). The bulking and post-buckling finite element analyses were performed to predict the static compressive strength of the selectively stitched stiffened panels. A good agreement was obtained between analytical and experimental results. The failure behaviors of the undamaged, CVFD and CVSD panels were also investigated.