Page 125 - 3D Fibre Reinforced Polymer Composites

114 30 Fibre Reinforced Polymer Composites

woven composite is normalised to the modulus of the equivalent 20 laminate. It is
important to note, however, that the 2D laminate is not always exactly equivalent
because the fibre contents of the 3D and 2D composites being compared are rarely the
same, and often differ by several percent. With the exception of a few outlying values,
it is seen in Figure 5.8 that the Young's modulus of a 3D composite is always within
20% of the modulus of the 2D laminate. Only rarely is the stiffness of a 3D composite
higher or lower by more than 20%. Figure 5.8 also shows that the Young's modulus of
a 3D woven composite is not influenced significantly by the z-binder content or fibre
structures (ie. orthogonal vs. interlock). The reason for the higher Young's modulus of
some 3D woven composites is probably due to a slightly higher fibre content than the
'equivalent' 2D laminate. The lower modulus of the other 3D woven composites is due
to higher fibre waviness of the load-bearing yarns caused by the z-binder.

r

-
a,
.-
0.75 A
a, 0
I- A
U - I 3D Orthogonal CarbonEpoxy (Chen et al., 1993)
.- - 0 3D Interlock CarbodEpoxy (Ding et al., 1993)
% 0.50
(d 0 3D Orthogonal Glas/Epoxy (Arendts et al., 1989)
E,
5 0.25 - 0 3D Interlock Glass/Epoxy (Arendts et at., 1989)
A 3D Orthogonal GlassNinyl Ester (Lee et al., 2002)
A 30 Interlock KevlarEpoxy (Guess and Reedy, 1985)
0.00' ' I ' I ' I " I I ' I ' I " J
*
'

Figure 5.8 Plot of normalised Young's modulus against z-binder content for various 3D
woven composites.

The micromechanical models described in Chapter 4 can be used to accurately
determine the Young's modulus of 3D woven composites. Even the simplest models,
such as the rule-of-mixtures, provide good estimates of modulus. As an example,
Figure 5.9 gives a comparison of the measured modulus for different types of 3D woven
composite against the theoretical modulus calculated using rule-of-mixtures. It is seen
that the agreement between the experimental and theoretical modulus values are within
10% in all cases.
Tan et a1 (2000a) measured the in-plane Young's moduli and Poisson's ratio for the
3D orthogonal woven CFRP composites as shown in Figure 5.6. Table 5.1 gives a