JEC COMPOSITES MAGAZINE - Issue #105 - June 2016 - 43

The mould used to manufacture the spoiler was provided by the
Espera Sbarro automotive design school. The spoiler consists of a
fibreglass-reinforced polyester laminate. It was prepared from 6 plies
of chopped strand mat. A thermosetting plastic (polyester resin)
was used for the matrix. A vacuum-assisted resin transfer moulding
(VARTM) manufacturing process was used. The fibre volume ratio
was around 35%. A blue gelcoat was applied on the spoiler top surface as a finish. A dedicated process based on the use of semi-finished
products was used to embed the piezoceramic discs, the connecting
system and the electrical conductor network between the first ply
and the second ply. The first ply was close to the top surface (gelcoat).
The 100 wires were carefully placed on the same spoiler edge. The
final product is shown in figure 2. Only 2 transducers were out of
order after 2 manufacturing trials.

Benefits and technical issues
Fig. 1: Architecture of a smart composite structure

Case study: smart automotive spoiler
A smart automotive spoiler was manufactured within the framework
of a project funded by the Labex ACTION programme. The spoiler
had to be able to damp effectively the guided waves propagating in
the structure. To this end, a specific decentralized control was used
[3]. The technical requirements for the composite spoiler were as
follows:
- a spoiler length of 1160 mm +/-1%;
- a wall thickness of 1.8 mm +/-30%;
- a network of piezoceramic discs embedded into the spoiler (50
units);
- transducers distributed as an array of 25 transducers in the extrados and an array of 25 transducers in the intrados;
- a matrix pitch of 60 mm +/-10%;
- each transducer is electrically independent and insulated from the
other ones (100 output wires);
- no local thickness modification allowed;
- only 3 transducers can be out of order.

Fig. 2: Smart automotive spoiler with 50 piezoceramic discs embedded

This case study highlights the technical issues and the benefits of a
smart composite structure with an embedded network of transducers.
When a smart composite structure is created, the transducers and
the electrical conductor network are usually glued onto the structure
to be controlled, and the electronics is located outside the structure.
The approach described in this paper is quite different, as it exploits
the integration capabilities provided by the composite material. The
idea was to protect the transducing elements and their electrical
connections and to industrially develop end products in a plug-andplay mode. Furthermore, the first step to develop programmable
or controllable matter with the ability to modify their intrinsic
material properties in real time is to integrate transducing elements
at the heart of the material through the integration of micro- and
nano-structures.
To integrate these new functionalities (for large structures in particular), it is necessary to develop a fully distributed set of transducers to
be embedded during the manufacturing process. To guarantee the
transducers' efficiency and preserve the geometrical and material
properties of the host composite structure, several major technical
issues were identified as having a strong impact on the manufacturing
requirements [4], including the need to:
- electrically connect a large number of transducers so as to act
on the whole structure. This is a requirement to take advantage
of a distributed network. With a distributed control network,
the structural behaviour of a system can be modified over a wide
excitation frequency range or, more generally, over a wide multi-physical excitation range;
- make each transducer electrically independent. This is particularly important when developing carbon fibre-reinforced
composite structures, which are naturally conductive. The use
of semi-finished products can provide a good electric insulation
solution;
- perfectly couple the exogenous element with the composite
material so as to guarantee the transducers' efficiency and
reduce the risks of delamination or other failures;
- accurately master the location of the transducers into the strucNo105 June 2016 /

jec composites magazine 43

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #105 - June 2016