SAMPE Journal - March/April 2017 - 8
Feature Article
Figure 2. Wide-range of laminate stiffness provided by three thick-thin ply combinations of C-Ply with simple 1- or 2-axis layup.
Universal Laminates
In a recent work published in
the literature, a novel invariantbased approach to describe elastic
properties and failure of composite
plies and laminates was proposed.
The trace of the plane stress stiffness
matrix was recommended as the
only material property needed
to understand the stiffness of
carbon/polymer composites and
their laminates6. With trace as the
normalizing factor of stiffness, all
CFRP can collapse onto one chart6,7.
One universal laminate "carpet plot"
will suffice. This is shown in Figure
1 for one bi-angle tape that has equal
thickness for both plies.
In Figure 1, universal tracenormalized laminate stiffnesses
(same for all CFRP) are shown
above the horizontal line. Absolute
stiffnesses for three representative
CFRP are show below the horizontal
line. One should note the similarity
of the curves for A11 and A66. They
differ only by their respective trace,
listed as the scaling constants on the
bottom line, from left to right, of 139,
206, and 218 GPa.
Layup ratios (the relative thickness
between the x- and y-axis layup)
listed are 1:0 (1-axis layup), 2:1 and
1:1 (2-axis layups), which are the
only practical options. Layup ratios
such as 3:1 and higher will make
homogenization of laminate in
both the in-plane and out-of-plane
directions more difficult for having
3 or more plies of [0]. When 3 or
more [0] plies are dispersed among
off-axis plies, the layup sequence is
more complicated. The deposition
rate will be reduced, and lamination
will be more prone to error. Nonhomogeneous laminates are not as
strong and tough and costlier than
homogeneous laminates.
Families of Sub-Laminates from ThickThin Ply Combinations and Layup
Ratios
Different
families
of
C-Ply
(Chomarat) bi-angle tapes can be
produced with different thicknesses
between the [0] and [±φ]. Two
simple variations plus the thick-thin
combination in Figure 1 are shown in
Figure 2, with the same notations of
off-axis angle [±φ] and layup ratios.
The example of Figure 1 is on the left
where "Thin-Thick" C-Ply is shown.
From Figure 2, nine families of sublaminates are shown resulting from
3 thick-thin ply combinations and 3
layup ratios of 1:0, 2:1 and 1:1. These
9 families are shown in Table 1. They
8
SAMPE Journal, Volume 53, No. 2, March/April 2017
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