Failure initiation in translaminar reinforced composites

A translaminar-reinforced (TLR) composite is an otherwise two-dimensional l aminate with through-thickness or Z-direction fibrous reinforcement across the lamina. Only small amounts (less than 5% volume) of TLR are necessary t o substantially improve compression-after-impact response, increase fractur e toughness, and severely restrict the size and growth of delamination. The se improvements have been documented repeatedly in the literature, and it i s generally accepted that TLR restricts the size and growth of delamination . In this paper we report a detailed investigation of whether TLR delays th e initiation of delamination via finite-element analysis and a strength-of- material approach. The various parameters investigated include TLR material , diameter, spacing, volume fraction, and through-thickness angle. In addit ion, the unavoidable microstructural features of curved in-plane fibers and resin pockets were examined. Our conclusion is that TLR does not delay dam age initiation, even though it has been shown experimentally to restrict da mage progression.