Effect of Z-pinning on the impact resistance of composite laminates with different layups

The paper presents the results of an experimental investigation into the effect of Z-pinning on the impact resistance of composite laminates with different multi-directional layups. Unpinned and pinned [0(2)/90(2)]s, [0(2)/ +/- 45]s and [0/ +/- 45/90]s carbon/epoxy samples were subjected to low-velocity impacts resulting in damage severities. ranging from barely visible damage to full laminate penetration. The responses to impact of the laminates were characterized in terms of damage evolution, load-carrying capacity, and resistance to perforation and penetration. It was found that even though Z-pins are not capable of delaying the onset of delamination, they significantly reduce delamination size for high-energy impacts. Z-pinning improves the resistance to perforation and penetration of [0(2)/90(2)]s, laminates, while It does not significantly affect that of [0(2)/ +/- 45]s and [0/ +/- 45/90]s samples. The dependence of the efficacy of Z-pins on the laminate layup is attributed to the different distribution of the delaminations through the thickness of the investigated laminates.