Page 118 - 3D Fibre Reinforced Polymer Composites

Chapter 5

3D Woven Composites

5.1 INTRODUCTION

3D woven composite is a new type of advanced engineering material that is currently
used in only a few niche applications. The most significant applications are stiffeners
for the air induct duct panels on the Joint Strike Fighter, aircraft wing joints on the
Beech Starship, and rocket nose cones. 3D woven sandwich composite reinforced with
distance fabric is also used in modest amounts, such as floor panels for trains, hard-tops
for convertible cars, and the deck and top-side structure for a fishing boat. While the
present use of 3D woven composite is limited, the potential use is impressive and wide-
ranging with various possible applications in the aerospace, marine, infrastructure,
military and medical fields. As described in chapter 1, in the future this composite may
be used in a diverse variety of items ranging from jet-engine components to personnel
body armour to artificial limbs.
While the future of 3D woven composites appears promising, it is not assured. Many
challenges are facing the increased application of this material. A major factor is that
the cost of 3D woven composites is currently higher than 2D prepreg or fabric laminates
for many applications. It was discussed in chapter 2 that the 3D weaving process has
the potential to reduce lay-up and assembly costs in fabrication, however 3D woven
fabric is not yet produced in large commercial quantities at low cost. Another
impediment to the increased use of 3D woven composite in the aircraft industry is the
high cost of certifying these and other new materials for primary load-bearing
structures. Until the cost savings and other benefits of 3D woven composite are fully
appreciated, then aircraft manufacturers will continue using conventional 2D laminates
in most composite components.
Another significant challenge is that many designers, fabricators and users of
composites are unsure of the potential benefits of using 3D woven composite. Most
sectors of the composite industry do not fully appreciate the benefits gained from using
3D woven material, such as reduced fabrication cost, greater design flexibility,
improved impact resistance, and superior through-thickness mechanical properties. The
design and fabrication of 3D woven composite is described in Chapter 2 and
micromechanical models for predicting their stiffness and strength are outlined in
Chapter 4. In this chapter the in-plane mechanical properties, delamination resistance
and impact damage properties of 3D woven composites are described. In Section 5.2
the microstructural features of 3D woven composites that affect the mechanical and
impact properties are described. This includes a description of microstructural damage
such as fibre crimping, fibre damage and z-binder distortion that degrade the in-plane
and through-thickness properties. The mechanical properties and failure mechanisms of
3D woven composites under tension, compression, bending, interlaminar shear and
fatigue loads are described in Section 5.3. Following this, the delamination resistance