Page 67 - 3D Fibre Reinforced Polymer Composites

56 30 Fibre Reinforced Polymer Composites
(1998), Parnas (2000) and Potter (1997) or directly from resin suppliers such as Hexcel,
3M, Dow Chemical, Bayer, Shell, etc.

Temperature T3 > T2 > TI

I
Time

Figure 3.5 Illustration of resin viscosity versus time

3.5 PREFORM CONSIDERATIONS

When liquid moulding is used to consolidate preforms constructed from 2D fabric, one
of the most important considerations is the need to keep the preform stable through a
means of binding the fabric layers together. Normally this is accomplished by the use of
a relatively small amount of binder resin which will be compatible with the matrix resin.
The use of 3D fibre preforms negates the need to use a binder resin as the 3D nature
of the fibre architecture creates an inherently stable preform. This is a major advantage
of these preforms over those produced from 2D fabric and can lead to significant cost
advantages when liquid moulding complex structures (Broslus 1991).
There are however some issues related to the liquid moulding of 3D fibre preforms.
Generally the preforms are not produced at the final fibre volume fractions required in
the composite structure thus pressure is often used to compact the preform to the
required fibre volume fraction. In 2D fabric preforms this is generally not a concern as
the pressure is usually applied normal to the fabric layers and thus does not affect the
fibre directions. However, with 3D fibre preforms not all the reinforcement wilI be
perpendicular to the pressure therefore the use of compaction pressure can lead to a
distortion of the 3D fibre architecture and thus a potential degradation of the composite
properties. An allowance for this possible distortion must therefore be made when
designing the preform architecture.