JEC COMPOSITES MAGAZINE - Issue #89 - May 2014 - 43

Fig. 2: Filament winding of an integrated isogrid
structure

Designing optimized isogrid structures was not the only challenge, one
also had to be able to manufacture
them. When designing with composites, design and manufacturing
interact with one another in the sense
that the feasible level of component
complexity depends on the availability of suitable equipment. Therefore,
a production technique allowing
CNC-controlled filament winding was
developed.

Out-of-autoclave process

Triangular pattern
Composite isogrid structures with triangular integral stiffening ribs (often
called stringers) are generally used in
lightweight applications. The triangular pattern is very efficient because it
provides rigidity while saving material and therefore weight. The term
"isogrid" is used because the structure
can act like an isotropic material, with
equal properties measured in any direction, and as a grid, referring to the
sheet and stiffener structure.
Isogrid configurations manufactured
by automated filament winding offer
extremely high strength-to-weight
ratios. Isogrid structures form selfstiffened structures combining low
weight with high stiffness, strength
and damage tolerance, which can be

Fig. 3: Composite isogrid structure

used in aircraft or space vehicle applications. Aerospace isogrid structures
include payload shrouds and boosters
that must support the full weight of
upper stages and payloads under high
g-force loads.
Other applications for integral composite isogrid structures include, for
example, sports equipment, rollers,
helicopter tailbooms, robot structures, satellite structures, unmanned
underwater vehicles (UUV) and
unmanned aerial vehicles (UAV). n

About CirComp
CirComp GmbH develops and manufactures components made of highperformance composite materials
for industrial, marine and aerospace
applications using out-of-autoclave
filament winding and resin transfer
moulding processes.

Fig. 4: Applications of integrated composite isogrid structures

No89 May 2014 /

More information:
www.circomp.de

Feature Aeronautics

With this manufacturing process,
continuous fibre rovings impregnated
with resin are applied onto a rotating mandrel along specified patterns,
following the isogrid structure. These
patterns cannot be chosen freely, as
they must adjust to manufacturing
and design boundary conditions.
If required, the isogrid structure
can be finished with an outer skin
manufactured by filament winding
immediately on top of the isogrid
structure. This results in an integral
isogrid structure with an outer skin in
a very cost-effective process. Curing
is performed in an out-of-autoclave
process.

The use of conventional mechanical
joints usually results in the cutting of
fibres, introduces a stress concentration factor and significantly reduces
the load-carrying capacity and the
lifetime characteristics of the whole
unit. It is well known that the proper
selection of a joint type makes it
possible to use composites in a loadcarrying structure more efficiently.
Therefore, metallic fasteners were
embedded around the fastener by
filament winding without cutting the
fibres to achieve high load transfer
together with a simple connection to
attach the composite isogrid structures.

jec composites magazine 43

http://www.circomp.de

JEC COMPOSITES MAGAZINE - Issue #89 - May 2014

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