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to-spar joints (Cacho-Negrete, 1982; Holt, 1992; Lee and Liu, 1990; Liu, 1990; Sawyer,
1985; Tada and Ishikawa, 1989; Tong et al., 1998; Whiteside et al., 1985). The
feasibility of joining and reinforcing the wing and fuselage panels for large commercial
aircraft using stitching has been evaluated as part of the ACT program (Palmer et al.,
1991; Dexter, 1992; Deaton et al., 1992; Jackson et al., 1992; Kullerd and Dow, 1992;
Markus, 1992; Suarez and Dastin, 1992; Jegley and Waters, 1994; Smith et al., 1994).
Stitching is being evaluated as a method for manufacturing the centre fuselage skin
of Eurofighter (Bauer, 2000). Stitching may be used for joining the stiffeners to
fuselage panels on Eurofighter, and it is expected to reduce the component cost by 50%
compared with similar stiffened panels made of prepreg laminate. Stitching is also
being evaluated for the fabrication of the rear pressure bulkhead to the Airbus A380
aircraft, a component measuring 5.5 m by 6.2 m (Hinrichsen, 2000).

1.2.5 3D %Pinned Composites
In the early 1990s the Aztex Corporation developed and patented Z-fiberm technology
for reinforcing 2D laminates in the through-thickness direction (Freitas et al., 1994). 2-
fibersTM are short pins made of metal wire or pultruded composite that can be inserted
through uncured prepreg tapes or dry fabrics to create 3D composites.
Z-pinning is a relatively new technology, and its full potential and applications is
still being evaluated. Composite structures such as hat-stiffened and T-stiffened panels
have been reinforced in the flange region with Z-fibresTM to demonstrate the
effectiveness of z-pinning to increase joint strength. The localised reinforcement of
flanges and joints with Z-fibersTM removes the need for fasteners or rivets and produces
a more even load distribution over the joined area. 2-pinning is also being used to
reinforce inlet duct skin panels and to fasten hat-shaped stiffeners to selected composite
panels on the F/A-18 SuperHornet fighter aircraft.