Impact and Compression-After-Impact Performance of a Thin Z-Pinned Composite Laminate

Impact and compression-after-impact (CAI) tests were carried out on [02/ ± 45]s carbon/epoxy samples to characterize the effect of z-pinning on the delamination resistance and damage tolerance properties of the laminate. Unpinned and z-pinned samples were subjected to impacts between 2 and 36 J to produce damage conditions that extend from barely visible impact damage (BVID) to complete penetration. The damage induced by impact and the damage modes leading to ultimate CAI failure were examined by Xradiography and by direct observations of the sample faces during CAI loading. The analyses indicate that the role of z-pins on the impact and CAI response of the laminate is dependent on the size and features of the damage. Z-pins do not modify the structural response to impact of the laminate, but they are effective in reducing the extent of damage for impact energies above a threshold value. Z-pinning is also effective in improving the CAI strength of the laminate for impact energies above this threshold value, even though it degrades the residual compressive strength for lower impact energies. Reductions in impact delamination size of up to 50% and improvements in CAI strength of about 20% were achieved by z-pinning for highenergy impacts. The mechanisms by which the z-pins affect the CAI response of the samples are illustrated and examined in detail for different impact damage severities.