Translaminar Reinforced Composites: A Review

Abstract

A trans-laminar-reinforced (TLR) composite may be defined as a composite laminate with up to 5% volume of fibrous reinforcement oriented in a translaminar or through-thickness direction. The TLR can be continuous threads as in 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, with the distinction that the material structure is a simple layered structure with only a few percent volume of reinforcement through-the-thickness. It has been repeatedly documented in the literature that adding either type of TLR to an otherwise two-dimensional laminate results in the following advantages: substantially improved compression-after-impact response, considerably increased fracture toughness in Mode I (double cantilever beam) and Mode II (end notch flexure), and severely restricted size and growth of impact damage and edge delamination. TLR has also been used to eliminate catastrophic stiffener disbonding in stiffened structures, and in cocured structures it may be used as a substitute for mechanical fasteners. TLR directly protects the Achilles' heel of laminated composites, that is, delamination. As little as 1% volume of TLR significantly alters the mechanical response of laminates. While there is a significant volume of literature, which is reviewed in this paper, there is still a very incomplete understanding of the mechanisms and parameters affecting those mechanisms responsible for the significant changes in the laminate response.