JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 33

thin-ply

New design opportunities
using thin-ply composites

By
Robin Amacher1,2, Wayne Smith1, John Botsis2, Clemens Dransfeld3, Joël Cugnoni2
1
North Thin Ply Technology SARL
2
Lab. of Applied Mechanics and Reliability
Analysis, EPFL, EPFL-STI_LMAF
3
Institute of Polymer Engineering, FHNW

For thin parts that are still achievable
with standard composites, the benefit in terms of design space is easy to

understand. The case of a 0.6-mm "quasiisotropic" laminate is a good example,
as there will be virtually no other choice
than to use a [0°/90°]s cross-ply using
160-gsm plies (Fig. 2). With 80-gsm
plies, it is already possible to switch to
a "real" quasi-isotropic stacking such as
[+45°/90°/-45°/0°]s, which is much closer to an isotropic behaviour, not only for
in-plane characteristics, but also in terms
of flexural properties. With 40-gsm plies,
one could make a [+45°/90°/-45°/0°]2s
or even introduce additional orientations. With 20-gsm plies, it would even
be possible to get rid of the symmetry
([+45°/90°/-45°/0°]8 for example) as

the number of plies would be sufficient
to avoid any warping during the cooling
stage [1].
When considering optimized orthotropic
laminates, the design space is expanding exponentially with decreasing ply
thickness, thus opening the door to a
vast set of new design opportunities. This
expanded design space is of particular
interest when taking into account the
stacking recommendations that are usual
for commercial aeronautics, such as the
"10% rule" (there should be at least 10%
of the plies in each of the 0°, 90°, +45° and
-45° directions) [2]. With this rule and

Fig. 1: Solar Impulse during one of its test flights in Switzerland

No96 April 2015 / jec

Feature Aeronautics

hin plies are essential for applications that need to be light
and feature very thin skins. Solar
Impulse (Fig. 1) is an example of such
an application that is designed to achieve
nonstop flight over days and nights using
only solar energy. It has a fundamental
requirement to be extremely light despite
a 72-m wingspan (as wide as or wider
than the world's largest commercial and
military aircrafts) and 633 kg of batteries.
Its total weight is only 2300 kg, ready to
fly. To achieve this outstanding result, it
is necessary for each part to use as little
material as possible. The spar boxes,
produced at Decision SA, use a construction that is transitioning from sandwiches with skins made of four 100-gsm
(grams per square metre) plies at +/-45°
in the centre of the wing to skins made
of only four 25-gsm plies at +/-45° at its
wingtips.

North Thin Ply Technology (NTPT) supplies a wide range of high
performance thin ply prepreg materials. Thin plies are now used
in a wide range of high-performance composite applications
such as aerospace, motorsport, sporting equipment and many
others. NTPT's thin ply technology is based on the concept of
plotting 2-dimensional multilayered preforms using unidirectional tapes and draping them in 3-dimensional moulds, with
the use of CNC equipment and automated handlers whenever
possible.

composites magazine 33

JEC COMPOSITES MAGAZINE - Issue #96 - April 2015

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #96 - April 2015