JEC COMPOSITES MAGAZINE - Issue #86 - January/February 2014 - 61

design

The composites design
and analysis challenge
Composites offer a host of advantages for companies
looking to reduce weight and increase performance of
their products. The aerospace industry had led the way
with the use of advanced composites but many other industries including energy, automotive, marine, and consumer products are increasingly looking at composites as
the new material of choice. With all of their advantages,
composites do offer some real challenges in regards to
design and analysis.

Design tools

raditional design tools are based
on isotropic materials and are
focused on documenting shape
and thickness of the part. For laminated
composites, you need tools that can work
with layered structures with 2D ply shapes
stacked on top of one another.

Analysis challenges
For analysis, the challenge with composites stems from the fact that the analyst
needs to consider many more variables,
which makes it difficult to determine the
right trade-offs to consider in improving the design. These analysis challenges
lead to "black aluminium" designs where
composite structures are designed with
quasi-isotropic material architectures and
as direct replacements of isotropic material designs. In these cases, we just take
advantage of the high stiffness-to-weight
ratio of composites and ignore the benefits composites can provide in regards to
material property tailoring.

Design optimization tools, such as Altair's
HyperWorks Suite and its optimization tool OptiStruct, can provide many
benefits to the designer and analyst of
composite structures. These tools can efficiently sort through the many design variables and provide guidance on optimal ply
shapes and laminate configurations. The
designer can provide inputs on geometry,
ply angles to consider, material properties, loads, and boundary conditions. The
designer also defines design constraints
such as displacement, stress, or strain
along with the objective, which is usually
to minimize the mass of the structure.

Composite optimization process
The composite optimization process involves the following 3 steps: 1) ply shape
optimization, 2) ply shape sizing, and 3)
ply order optimization. Ply shape optimization uses a combination of topology and
topography optimization methods known
as composite free-size optimization. Once
the composite panel geometry is defined,
a finite element shell mesh is applied to

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the geometry, the user selects the ply
angles to be considered, defines the loads
and boundary conditions on the panel,
defines any structural constraints (e.g.
buckling), defines any manufacturing constraints for the application, and selects the
objective function (e.g. minimize mass).
The manufacturing constraints can be a
requirement to balance the laminate or ply
pairs (e.g. ±45° plies), set a minimum or
maximum thickness for any given angle,
or set a minimum or maximum thickness
of the laminate. The user also selects the
number of ply shapes that are desired (e.g.
four shapes per ply angle). The ply shape
optimization routine then produces a set
of ply shapes for each angle per the parameters set by the user.
From this step, the ply shape sizing is
carried out. The user first determines if
the ply shape optimization definitions are
acceptable or if modifications are desired.
In some cases, the designer may want to
modify the ply shapes for manufacturing
or other considerations.
Once the final ply shapes are determined,
the next step is to size the ply shapes. In

No86 January - February 2014

/ jec composites magazine 61

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

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #86 - January/February 2014