Failure Initiation in Translaminar Reinforced Composites

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