Page 145 - 3D Fibre Reinforced Polymer Composites

134 30 Fibre Reinforced Polymer Composites

the shortcomings of conventional sandwich composites, which consist of two thin
laminate face skins that are adhesively bonded to a light-weight core of honeycomb or
rigid foam. The disadvantages of standard sandwich materials is that the manufacturing
process can be labour intensive because the skins must be manufactured separately and
then bonded to the core in a second processing step. Consequently, sandwich
composites can be expensive to manufacture for low-cost applications such as civil and
marine structures. Further problems with sandwich composites are that they are
susceptible to skin-to-core separation due to bond-line defects and experience skin
delamination under excessive bending, buckling or impact loads.
Advanced sandwich composites made of distance fabric offer the potential to
overcome these problems. The 3D fibre architecture of a distance fabric is shown
schematically in Figure 2.1 1, and is characterised by through-thickness fibres, known as
piles, interconnecting two woven face skins. The fabric is produced using the velvet
weaving process that is described in Chapter 2, and the process can be controlled to
produce fabrics with different amounts and orientations of the pile yams. After
weaving, the hollow core of the fabric can be filled with a polymer or syntactic foam by
liquid foam injection. The skins can be impregnated with thermoset or thermoplastic
resin using the moulding processes outlined in Chapter 3.

10000 -
2D Laminate
-------- 3D Orthogonal Composite
N- ...-
E 8000 _.......a. 0 3D Interlock Composite
E
Y
a
2
a, 6000-
tJ)
a
Em
2 4000-
kl
z
-
2000 -

0
100 150 200 250 300 350
Impact Velocity (m/s)

Figure 5.25 Effect of impact velocity on the amount of delamination damage to 2D and
3D woven composites (Data from Billaut and Rousell, 1995).