JEC COMPOSITES MAGAZINE - Issue #95 - Special JEC Europe - March 2015 - 91

In-service behaviour
Composite structures show a quite
different damage behaviour compared
to metals. There are no plastic deformations after an impact, but delamination
can occur without visible damages.

Fig. 7: Left: Thermoplastic unidirectional tapes; right: Braided tape preform (top); consolidated braid based
on tapes (bottom)

the roving over the preforming technology to the injection or consolidation are
mandatory.

Design and calculation

Fig. 8: Simulation chain

turing process chain and therefore leads
to higher production costs.
SGL Group currently has different
research and development activities
ongoing together with the Technical
University Munich and the University
of Stuttgart in order to apply superior
pre-impregnated yarns like thermoplastic
UD tapes (see Figure 7 left) to braiding
processes (see Figure 7 right).
It turned out that it is in principle feasible to process pre-impregnated materials
with textile technologies like braiding
or tailored fibre placement (TFP).
However, process and machine adjustments, as well as material customization
to these processes, are required in order
to achieve the highest production rates
and failure rates suitable for industrial
processes.
Which technology and technology
family, respectively, will finally be the
technology of choice depends on the
geometries and the required production
rates. In all cases, process chains from

The continuous improvement of engineering design concepts is very important; taking loads, geometries, production numbers and process technology
into account to get rid of the black-metal
design. This has to be accompanied by
the development of simulation tool
chains for process simulation (draping,
injection, and curing) and structural
simulation (static, fatigue, impact, and
crash). In this discipline, there is probably the most significant commonality of
the aerospace and automotive industries.
In aerospace, the demanding certification procedure is often the driving
factor.
Therefore, a conservative design approach is mandatory, which leads to a
design for mainly static requirements
and no further fatigue substantiation.
Crash requirements are rather moderate in comparison to automotive, while
high-velocity impact in flight and general
damage tolerance requirements are more
important.
Crash simulation is still the most challenging for automotive applications of
CFRPs, regarding not only numerical
methods but also input data for material
models. Furthermore, issues like contact
corrosion and different thermal expansion coefficients have to be considered
for multi-material concepts.

This has to be considered by a damagetolerant design of the structures. For
non-destructive inspection, technologies
like ultrasonics and thermography are
available from aerospace experience. For
automotive applications, these methods
have to be adapted to the specific industry and market needs. Over the long
term, health monitoring systems may be
applied - for example, integrated sensors
based on hollow glass fibres or piezo
ceramics can be integrated in composite
structures to report damages.
Repair methods can also be adapted
from aerospace to the automotive needs,
especially regarding the recently developed robot-assisted automated repair
methods. But the replacement of damaged structures and integration of spare
parts is also a promising and probably
more cost efficient way.

Recycling
Due to the long product lifetime and
comparably lower volumes, recycling is
not a critical issue for aerospace. Because
of governmental regulations, this situation is totally different for automotive.
With respect to potential technologies,
pyrolysis is most promising and already
in use at the prototype level. Further
developments are conducted in order
to improve the mechanical behaviour of
fibres after recycling by optimizing the
recycling process. In parallel, technologies have to be developed to produce
valuable preforms based on recycled
carbon fibres.
In any case, the reduction of production
scrap is still the most efficient way; for
example, by applying near-net shape
preforming technologies. n

No95 March 2015 /

More information:
www. ifb.uni-stuttgart.de

jec composites magazine 91

http://www.ifb.uni-stuttgart.de

JEC COMPOSITES MAGAZINE - Issue #95 - Special JEC Europe - March 2015

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