Page 218 - 3D Fibre Reinforced Polymer Composites

Z-Pinned Composites 207

The process begins by overlying an uncured composite prepreg laminate with an elastic
foam preform containing a grid of Z-fibersTM. The purpose of the foam is to keep the
rods in a vertical position and to stop them from buckling as they are embedded into the
composite. Once the preform is in position it is compressed under pressure from the
autoclave which forces the pins into the underlying composite (shown as step 2 in
Figure 9.2). The pins are chamfered at one end to an angle of about 45' to easily pierce
the composite. The benefit of inserting the pins within an autoclave is that the
composite can be heated to reduce the viscosity of the resin matrix. This allows the Z-
fibersTM to penetrate more easily and thereby reduce the amount of fibre damage to the
composite. After the pins are embedded in the composite the residual foam is removed
and the fabrication process is complete (step 3 in Figure 9.2). Any excess pin material
that is protruding above the composite surface can be easily removed using a shear
cutting tool.

Ultrasonic Insertion Transducer

I

, Z-Fibre Preform

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Uncured Composite

Remove Used Preform

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(a) Primary Insertion Stage & Residual Preform Removal

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(b) Secondary Insertion Stage
Figure 9.3 Schematic of the Z-fibreTM insertion process using UAZ. (Adapted from
Freitas et al., 1996)