Page 219 - 3D Fibre Reinforced Polymer Composites

208 30 Fibre Reinforced Polymer Composites

Alternatively, the pins can be inserted into uncured prepreg laminates without an
autoclave using a specially designed ultrasonic tool, as shown in Figure 9.3. This
method of pinning is known as the ‘Ultrasonically Assisted Z-FiberTM (UAZ) process’.
In the UAZ process the foam preform is partially compacted under the pressure of high
frequency acoustic waves generated by the ultrasonic tool. This forces the pins partway
into the composite, and at this stage the residual foam is removed and a second pass is
made with the ultrasonic tool to drive the pins completely into the composite.
Z-fibersTM can be inserted into most types of FRF’ materials, including uncured tape
laminates, pre-consolidated thermoplastic composites, cured thermoset composites, and
dry fabric preforms. (Z-fibersTM can also be used to reinforce and bond aluminium sheet
laminates (Freitas and Dubberly, 1997)). Z-fibersm are made of protruded composite
material or metal rod and range between 0.15 and 1.0 mm in diameter. Composite
materials used in Z-fibersTM include high-strength carbodepoxy, high-modulus
carbodepoxy, carbordbismaleimide (BMI), S-glass/epoxy, and silicon carbideBM1.
The metal pins are made of titanium alloy, stainless steel and aluminium alloy. The
amount of Z-fibersTM used for pinning composites is normally in the range of 0.5% to
5% of the total fibre content, although it is possible to have a greater amount for high
through-thickness reinforcement.

Figure 9.4 Z-pins in a composite (Courtesy of the Cooperative Research Centre for
Advanced Composite Structures Ltd)

The fibre structure of a composite reinforced with Z-fibersTM is shown in Figure 9.4.
The pins extend through-the-thickness of the composite, and are usually inclined at a