Page 216 - 3D Fibre Reinforced Polymer Composites

Chapter 9

Z-Pinned Composites

9.1 INTRODUCTION

The technology of reinforcing composites in the through-thickness direction with small
pins was first evaluated in the 1970s. Thin steel pin wires were inserted at offset angles
of k45O into carbodepoxy prepreg laminates to improve the delamination toughness
(Huang et al., 1978). The pins used were very thin, with a diameter of only 0.25 mm, to
minimise damage to the laminates. The steel pins were effective in increasing the
interlaminar shear strength and delamination resistance. However, initially it was
neither practical nor cost-effective to insert thin pins over a large area of composite
material, and therefore the technology was not immediately taken-up by the aircraft
composites industry.
Z-pinning technology was developed further in the early 1990s by Aztex Inc. The
technology involves embedding small diameter pins, known as Z-fibersTM, into
com osites to produce a 3D fibre network structure, as illustrated in Figure 9.1. Z-
fiberL technology is the newest of the various techniques for producing 3D
composites, and already it has a wide variety of potential applications in engineering
structures. An important potential use of Z-fibersTM is for the attachment and
reinforcement of composite joint structures such as lap joints, T-joints and rib stiffeners.
Z-pins are being used to fasten hat-stiffened sections to the composite skins in selected
parts of the F/A-18 Hornet fighter aircraft. Z-fibersTM can be used in composite joints
in place of bolted fasteners or rivets to provide a more evenly distributed load over the
joint area. Z-fibersTM can also be used for the local reinforcement of composite panels
to reduce the incidence of edge delaminations as well as the reinforcement of sandwich
panels to minimise the likelihood of skin peeling and debonding.

Figure 9.1 Schematic illustration of a z-pinned composite

The relatively recent development of Z-fibersTM has meant that z-pinned composites
have not been explored in detail. In this chapter the current state of knowledge of z-