Translaminar reinforced composites: A review

A trans-laminar-reinforced (TLR) composite may be defined as a composite la minate with up to 5% volume of fibrous reinforcement oriented in a translam inar or through-thickness direction. The TLR can be continuous threads as i n stitched laminates, or it can be discontinuous rods or pins as in Z-fiber materials. These materials may be considered a subset of 3D composites, wi th the distinction that the material structure is a simple layered structur e with only a few percent volume of reinforcement through-the-thickness. It has been repeatedly documented in the literature that adding either type o f TLR to an otherwise two-dimensional laminate results in the following adv antages: substantially improved compression-after-impact response, consider ably increased fracture toughness in Mode I (double cantilever beam) and Mo de II (end notch flexure), and severely restricted size and growth of impac t damage and edge delamination. TLR has also been used to eliminate catastr ophic stiffener disbonding in stiffened structures, and in cocured structur es it may be used as a substitute for mechanical fasteners. TLR directly pr otects the Achilles' heel of laminated composites, that is, delamination. A s little as 1% volume of TLR significantly alters the mechanical response o f laminates. While there is a significant volume of literature, which is re viewed in this paper, there is still a very incomplete understanding of the mechanisms and parameters affecting those mechanisms responsible for the s ignificant changes in the laminate response.