Page 124 - 3D Fibre Reinforced Polymer Composites

30 Woven Composites I13
5.3 IN-PLANE MECHANICAL PROPERTIES OF 3D WOVEN COMPOSITES

5.3.1 Tensile Properties
The tensile properties and failure mechanisms of 3D woven composites have been
investigated since the mid-l980s, but only recently has an understanding of their tensile
performance began to emerge. Tensile studies have been performed on 3D woven
composites with orthogonal or interlock fibre structures made of carbon, glass or
Kevlar. Numerous studies have compared the tensile properties of 3D woven
composites against 2D laminates with a similar (but not always the same) fibre content,
and different results are reported. The Young’s modulus of some 3D woven composites
is lower than the modulus of their equivalent 2D laminate. This difference is shown by a
comparison of tensile stress-strain curves for a 2D and 3D woven composite in Figure
5.7. This data from Lee et al. (2002) shows that the Young’s modulus of the 3D
composite is about 35% lower than the 2D laminate. Other tensile studies also report
that the Young’s modulus of a 3D woven composite is lower than a 2D laminate, with
the reduction ranging from -10% to 35% (Ding et al., 1993; Guess and Reedy, 1985).
However, in some cases the tensile modulus of the 3D woven composite can be slightly
higher than the 2D laminate (Arendts et al., 1989; Chen et al., 1993).

400 r 7D Wm

h 350
m
a
300
v)
8 250
L
65
Q) 200
-
.-
(0
$ 150
I-
Onset of Plastic Tow Straightening

O V ‘ I I I I I
0 1 2 3 4 5
Strain (%)

Figure 5.7 Tensile stress-strain curves for a 2D and 3D woven composite.

The Young’s modulus values for a variety of 3D woven composites are plotted against
their z-binder content in Figure 5.8. In this figure the Young’s modulus of the 3D