JEC COMPOSITES MAGAZINE - Issue #89 - May 2014 - 30

CMC

- oxide matrix
The material's behaviour is similar to
that of the preceding family, but the
matrix consists of a specific sequence of
Si-B-C base layers. The boron reacts with
oxygen, leading to the formation of a
borosilicate glass that fills in cracks in the
matrix and keeps the oxygen from diffusing down to the fibres. This mechanism
is called "self-healing" (or self-repair),
and occurs with sufficient kinetics for
temperatures over 500°C.

The DTP project
on nozzles for civilian use
This DTP project is Safran's first one in
civil aviation applications. The project
came up against three specific aspects
that needed to be considered, relative to
the military applications Herakles was
accustomed to:
- longer service life,
- working with complex shapes,
- the need for very competitive prices.
The project used the material currently
considered to be the benchmark for the
SiC fibre based afterbody application
(Cerasep® A40C), with the following
results from the ground test series:
- validation of mixer architecture,
- good static and dynamic behaviour,
- capability to create a large complexshape part demonstrated,
- validation of integration with engine,
- capacity to carry out endurance tests:
708 durability cycles - 220 hours of rotation, including 70 hours at max power.

The Arcoce programme
After this first successful phase, the next

CMC mixer on a CFM56-5C engine on ground
test bench (Snecma Villaroche)

step was to validate the
concept for the current
benchmark material
by further improving
its oxidation resistance
throughout the range
of application and by
using cheaper, more
industrial processes.
These challenges are
being addressed within
the Arcoce programme
by the Aerospace
Valley project, which is
sponsored by the French
Investment Office (CGI),
the Ministry of Economy, Exploded view of the Arcoce demonstrator plug
Industrial Renewal &
the Digital Economy and the Aquitaine
kg, or a weight savings of more than 35%
Regional Council.
for isofunctionality.
Joint analysis from the DTP project on
nozzles for civilian use and previous projects on the state of the art revealed some
technological bottlenecks, which were
made the focus of the Arcoce research
programme. The bottlenecks were identified at three levels:
- technologies (acoustic in particular),
- materials with augmented maturity (in
particular for damage tolerance),
- processes that are under control and
which could be industrialized and
partly transferred over time to small and
medium-sized businesses.
With regard to the metallic CFM 56-5B
plug: shifting from the Inconel material to the CMC material led to weight
savings that made it possible to integrate
a low-frequency acoustic absorber. The
absorber consists of large CMC boxes
that communicate with the primary flow
via microperforated skins (6 skins with
15,000 holes each, for a 20% opening
rate).
The Arcoce plug weighs 24 kg (including
6 kg of metal support) for a specification
of 24.5 kg (metallic plug without acoustic absorber). The CMC plug without
acoustic absorber weighs an estimated 15

30 jec composites magazine / No89 May 2014

These weights are measured or estimated
based on an imposed engine rear frame,
specifically the CFM56-5B engine rear
frame. If it had been possible to modify
this rear frame to better integrate the
attachment of the CMC plug, there could
have been a further weight savings of 3
kg. This indicates a need in future developments to work closely with engine
specialists and aircraft manufacturers,
using concurrent engineering.
The design of this demonstrator also
benefited from a design to cost approach,
since the demonstrator is meant to pave
the way for future development parts,
and then series parts.
After validation of the demonstrator, it
was subjected to a battery of ground tests
for performance and endurance. The
plug underwent more than 100 C cycles,
including more than ten hours of take-off
regime.
The next battery was of acoustic tests to
verify the low-frequency acoustic gain
(GE Peebles test operation). The target
gain was confirmed, validating both the
design for that aspect and compliance of
the fabrication with the design.
The full battery of ground tests took 53
JEC COMPOSITES MAGAZINE - Issue #89 - May 2014

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