IMPROVEMENT OF LOW-VELOCITY IMPACT ANDCOMPRESSION-AFTER-IMPACT PERFORMANCEBY Z-FIBRE PINNING

摘要

Z-fibre pinning is a new method of through-the-thickness reinforcement of laminatedcomposites. This paper presents an experimental test and theoretical analysis on how and why thesepins can improve the resistance to impact loading and damage tolerance under post-impactcompression. Specimens were made of carbon/epoxy T300/914 with nominal thicknesses of 2, 4, and 6mm. For the specimens tested in this study, z-pinning reduced impact damage area by 19-63%depending on the specimen thickness and impact energy. The CAI failure strains for the unpinnedsamples were about 0.6% while all the pinned strains were above 0.9%. If a factor of 1.5 wereintroduced to account for manufacturing differences and hot/wet performance of the laminate, aconservative design strain to failure limit would be 0.4% for the unpinned specimens and 0.6% for thepinned laminates. This indicates that the use of z-pins could increase the design strain limit from thecurrently accept level of 0.3-0.4%. All of these observations are discussed in the context of theoreticaland numerical models that have been advanced to predict the critical impact force and z-pinperformance in terms of laminate stiffness and the fracture toughness of mode-I delamination with thez-fibre bridging effect.