JEC COMPOSITES MAGAZINE - Issue #86 - January/February 2014 - 62

design

Fig. 1: Composite optimization process

this step, additional constraints can be applied to the problem (e.g. a strain constraint
on the fibre) and the problem is re-run.
Again, the objective function must be defined such as to minimize mass. The results
of this step give the number of plies to cut
for each shape.
The final step consists in taking the ply
information and then applying ply order
optimization to define the final lay-up
definition of the structure. The ply order
optimization method can take into account
different requirements such as a limit on
the number of adjacent plies with the
same angle, a constraint on which angle to
have on the outside of the laminate and/
or which stack to have in the core of the
laminate. The entire design process using
this optimization method is shown in Figure 1 where the application is an open-hole
tensile coupon.

structure that would meet the performance
of the aluminium structure was designed.
This resulted in a mass savings of 14%.
The second iteration allowed for ply shapes
to be optimized for each of the 4 angles
considered in the laminate (0/+-45/90).
In this case, the optimizer builds up plies
where it needs additional strength, drops
plies in areas where it can, and preferentially adds plies with the angles that it needs
to align best with the load direction in that
area. Manufacturing constraints are used
to make sure that the optimized structure
meets with manufacturing considerations

A 36% mass saving
This process was recently demonstrated
on a composite aircraft fuselage section
containing the aircraft door. For this application, a single load case of the internal
pressure was considered. An analysis of the
aluminium design was carried out so that
the performance of the composite panel
would be equivalent to the aluminium
design. For the first iteration, a "black
aluminium" design process was used
where a constant-thickness, quasi-isotropic

Fig. 2: Design results for an airplane door panel

62 jec composites magazine / No86 January - February 2014

on ply drop ramp rates. The resulting
structure resulted in a mass savings of 20%
over the black aluminium design and 36%
over the original aluminium design. An
overview of the design results is shown in
Figure 2.
The above example was for a single load
case. Even greater benefit from this method
will be realized with multiple load cases
which are common for most engineered
structures. The method also enables
engineers to consider more angle options
for plies which can add further structural
efficiency.
With these tools, we can begin to truly
harness the full power of composites.
Composite materials are found throughout nature: bones, tress, and shells align
stiffness where it is required and eliminate
material where it is not required. Nature
goes through an evolutionary process to
adjust the design to efficiently meet the
needs of the structure. Design optimization methods for composites get us close
to a virtual evolutionary process using
mathematical algorithms so we can design
minimal weight composite structures that
are optimized for performance and function just as we see in the natural composite
structures around us every day. n
More information:
www.altair.com
altairenlighten.com
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JEC COMPOSITES MAGAZINE - Issue #86 - January/February 2014

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