Improvement of low-velocity impact and compression-after-impact performance by z-fibre pinning

Z-fibre® pinning is a new method of through-thickness reinforcement of laminated composites. This paper presents an experimental test and theoretical analysis on how and why these pins can improve the resistance to impact loading and post-impact compression. Specimens were made of carbon/epoxy T300/914C with nominal thicknesses of 2, 4, and 6 mm. For the specimens tested in this study, z-pinning reduced impact damage area by 19–64% depending on the specimen thickness and impact energy. Experimental results obtained also indicate that z-pins can significantly increase the compression-after-impact (CAI) strength by about 45%. In this paper all of these observations are discussed in the context of theoretical and numerical models that have been developed previously to predict the critical impact force and z-pinning performance in terms of the laminate in-plane stiffness and mode I delamination fracture toughness with the z-fibre bridging effect.