JEC COMPOSITES MAGAZINE - Issue #88 - April 2014 - Special JEC Americas Spring Edition - 35

theory is that testing and certification can be
simplified and improved in terms of quality
and reliability. Testing laminates has many
advantages. First, it is closer to how composites will be used in structures. It bypasses
many thorny analytical models that are often
empirically based. Examples include in-situ
properties, processing variations from autoclave, vacuum bagging and liquid moulding,
manufacturing defects, out-of-plane properties, early failures such as micro-cracking and
delamination, and residual stresses. With
trace, we may be able to track the effects
of hot-wet conditions, impact and fatigue.
Thus, the tests on one laminate can be used
to scale how other laminates and materials
will behave. It is like aluminium alloys. A
material substitution from one alloy to another does not call for the structural design
to change. In the optimization of composite
structures, the same material to material and
laminate to laminate scaling is expected to be
in operation. Such a strict order plus C-Ply
can make composites competitive.

Conclusions

such as shear tests are not necessary. Test
coupons from laminates are preferred over
those from unitape. In fact, 4-point flexural
tests deserved more attention. A rational
order based on trace is now available to compare different materials or the same material
under different processing (autoclave versus
vacuum bagging), environmental (hot-wet)
and loading conditions (fatigue, impact).
C-Ply not only offers high-quality plies
through Chomarat's tow spreading technology. With only 2 plies in the basic building
block of [0/j] and [0/-j], the final composite component can often be produced
with a 1- or 2-axis layup. The cost savings or
productivity increase can be by one order of
magnitude. Some highlights are summarized
in Figure 8. We expect that the introduction of C-Ply to industry will be accelerated
through the collaboration among Chomarat,
the Stanford Composites Design Group and
its global research team. Our team stands
ready to supply C-Ply products, samples,
and design and manufacturing technology
and tools to interested parties. n

More information:
www.stanford.edu/group/composites

Composites Design
Workshop X
For those interested in learning more
about the new trace-based theory on
composites, the online Composites Design
Workshop may offer the best training for
this theory and tools to engineer C-Ply
tapes for the production of composites
structures. Training and tools are also
available from Think Composites, headed
by Thierry Massard in Paris.

Acknowledgements
The author wishes to acknowledge help for
the preparation of this work from Chomarat,
Hexcel, Bob Skillen of VX Aerospace, Alan
Nettles, Daniel Melo, Guilio Romeo, and
many others.

No88 April 2014 /

Special JEC Americas 2014

Composites are made simpler, easier,
stronger, lighter, cheaper, safer, ... by using C-Ply because it makes it possible to
replace conventional unitape with bi-angle
NCF, a building block from which many
laminates can be produced. The off-axis
angle is used as a continuous variable, not
just fixed at 45 degrees, to achieve a wide
range of continuous properties to meet
loading and environmental requirements.
The starting plies can be thick and thin to
further expand the realm of properties. Such
plies offer homogenization as a key to many
laminate performance properties that cannot be achieved with conventional stacking
sequence dependent laminates. Homogeneous laminates are stronger and tougher, and
can be produced using a labour saving and
simpler asymmetric nonstop layup, not to
mention the opportunity to be optimized
for tapering. Sangwook Sihn has demonstrated that for a cantilever beam under
uniform loading, the minimum weight saving for carbon composites can be 1/3 over
aluminium. With orthotropy, it can easily
reach 1/2. With invariants, tests are simpler
and faster. First of all, more difficult tests

Fig. 8: Many opportunities to make composites competitive and affordable, particularly with C-Ply

jec composites magazine 35

http://www.stanford.edu/group/composites

JEC COMPOSITES MAGAZINE - Issue #88 - April 2014 - Special JEC Americas Spring Edition

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