Page 22 - 3D Fibre Reinforced Polymer Composites

Introduction 11
In the non-aerospace field, 3D braided composite has been used in propeller blades for a
naval landing craft (Maclander et al., 1986; Maclander, 1992). There is also potential
application for 3D braided composite on ships, such as in propulsion shafts and
propellers (Mouritz et al., 2001). 3D braided composite has been used in truss section
decking for light-weight military bridges capable of carrying tanks and tank carriers
(Loud, 1999). Other potential applications include military landing pads, causeways,
mass transport and highway bridge structures when bonded to pre-stressed concrete. 3D
braided composite also has potential uses in the bodies, chassis and drive shafts of
automobiles because they are about 50% lighter than the same components made of
steel but with similar damage tolerance and crashworthiness properties (Brandt and
Drechsler, 1995). 3D braided composite has also been manufactured into a number of
biomedical devices (KO et al., 1988).

1.2.3 3D Knitted Composites
3D knitted composite has a number of important advantages over conventional 2D
laminate, particularly very high drape properties and superior impact damage resistance.
Despite these advantages, there are some drawbacks with 3D knitted material that has
limited its application. A number of aircraft structures have been made of 3D knitted
composite to demonstrate the potential of these materials, such as in wing stringers
(Clayton et al., 1997), wing panels (Dexter, 1996), jet engine vanes (Gibbon, 1994;
Sheffer & Dias, 1998), T-shape connectors (King et al., 1996) and I-beams (Sheffer &
Dias, 1998). This composite is under investigation for the manufacture of the rear
pressure bulkhead to the new Airbus A380 aircraft (Hinrichsen, 2000). The potential
use of 3D knitted composite in non-aerospace components includes bumper bars, floor
panels and door members for automobiles (Hamilton and Schinske, 1990), rudder tip
fairings, medical prothesis (Mouritz et al., 1999), and bicycle helmets (Verpoest et al.,
1997).

1.2.4 3D Stitched Composites
The stitching of laminates in the through-thickness direction with a high strength thread
has proven a simple, low-cost method for producing 3D composites. Stitching basically
involves inserting a fibre thread (usually made of carbon, glass or Kevlar) through a
stack of prepreg or fabric plies using an industrial grade sewing machine. The amount
of through-thickness reinforcement in stitched composites is normally between 1 to 5%,
which is a similar amount of reinforcement in 3D woven, braided and knitted
composites.
Stitching is used to reinforce composites in the z-direction to provide better
delamination resistance and impact damage tolerance than conventional 2D laminates.
Stitching can also be used to construct complex three-dimensional shapes by stitching a
number of separate composite components together. This eliminates the need for
mechanical fasteners, such as rivets, screws and bolts, and thereby reduces the weight
and possibly the production cost of the component. If required, stitches can be placed
only in areas that would benefit from through-thickness reinforcement, such as along
the edge of a composite component, around holes, cut-outs or in a joint.
A variety of 3D composite structures have been manufactured using stitching, and
the more important stitched structures are lap joints, stiffened panels, and aircraft wing-