Composites i Aerostructures
Designs on composites
Morson Projects’
aerospace technical
director, Syd Carson
discusses the
considerations that need to
be made when designing
for the manufacture of
composite aerostructures.
Addressing the process: Morson Projects use software programmes like Vistagy’s FiberSIM
C
omposites have quickly become a hot topic in the resulting in costly repair and maintenance work. Therefore, it
aerospace industry, replacing various metallic materials is important to identify any points on the structure that may
in many new aircraft applications. On the Boeing 787 suffer from moisture in the environment during the design
for example, composites account for 50% of the aircraft’s stage so that these sections can be reinforced to avoid any
structural weight, and with the only visible metal on the leading unnecessary damage.
edges and engine pylons, the aircraft has paved the way for A further shortfall with composites is that they can be
future programmes. more susceptible to impact damage than metal structures,
Constructing an entire composite fuselage from nose to tail and repairing carbon fibre sections is a much more complex
involves multiple sets of design and structural specifications, process. The most common type of damage to civil aircraft is
utilising a variety of manufacturing methods. As a result, from forklift trucks while the aircraft is stationary, with debris
Morson Projects stresses that design engineers need to ensure on the runway also a major issue. This is compounded by the
they have a full understanding of the manufacturing process fact that damage to composite components is not always visible
before undertaking any design projects. to the naked eye, and that damage to carbon fibre can appear
One aspect is the significant reduction in part count. as a small dent on an exterior surface, but be much more
While a typical metal fuselage requires over 100 metallic extensive on the interior.
sheets compared with around three carbon fibre cloths for Such damage results in complex repair work, where the best
a comparable structure, manufacture is still just as labour course of action is always to use the original fibres and fabrics
intensive as the design process inevitably becomes much more to meet all the original design requirements for the structure.
complex due to the way that carbon fibre material behaves As such, it is of paramount importance that repair schemes are
during the manufacturing process. considered in parallel to the initial design of the structure to
There are several key things to consider. Carbon fibre cloth ensure that any damage that may occur can be catered for.
is soft and pliable when in use, meaning it is prone to creasing, Finally, while composite manufacturing is currently still an
rippling and bridging, particularly when laying complex expensive investment, lifecycle costs are now recognised as far
boundaries such as corner treatments and around doors more important than initial manufacturing costs. Aircraft need
and windows. This wrinkling effect may affect the strength, to be in service for 25 years so it is important to select the most
stiffness and fatigue resistance of the final product, so it is effective manufacturing process that will see structures retain
essential that fibre placement on large fuselage panels or wing their performance and strength over this period.
skins undergoes a comprehensive simulation early in the design Inevitably though, as the volume of composite manufacturing
stage to avoid fibre deformation wherever possible. Failure to grows, production costs will decrease. This in turn will mean
do this properly can be extremely costly as failures often do not that the size and complexity of composite aerostructures will
come to light until physical testing. increase and continue to challenge composite engineers long
Carbon fibre can also be prone to absorbing moisture which into the future. ❙
can lead to degradation of the material as layers come apart, www.morson-projects.co.uk
AEROSPACEMANUFACTURING | MARCh 2010 35
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