JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020 - 65

Optimization approach for designing composite components

This approach has two main disadvantages:
- The prototype could meet the minimum requirements even
if the experimental results diverge from the calculations. This
may be due to the use of excessively conservative safety factors
or an incorrect model. This makes it difficult to identify whether the model is representative or not.
- The components produced according to this strategy show a
low cost-performance ratio since they are not optimized.
Moreover, with the traditional approach, it is not possible to
find an optimized product later without redoing the whole project from the beginning stage (dashed line in Figure 1).

The optimization design approach
Instead, using the optimization approach makes it possible to
find the best design to meet the minimum requirements while
reducing costs or to find the best design to maximize performance. Unlike the traditional approach, if the prototype does
not meet the requirements, the model can be tuned to match
the experimental results. When all the requirements are met,
the product is fully optimized.
As can be deduced from Figure 1, if the creation time of a parametric model (generally more complex than a standard one)
plus the optimization time plus the model's tuning time is less
than the time needed to develop a standard model plus the calculation time plus the modification time, the optimization approach is always preferable. This approach may be
preferable even if the time required is greater since the cost savings can be substantial on a large number of products.
This method can also be useful to produce a small batch of very
expensive products. In this case, making attempts or following
a traditional design approach is too risky for the company since
each prototype is very expensive.
Figure 2 shows an example of a product developed by Reglass
HT (Minerbio (BO), Italy) that was optimized in the initial design stage to minimize the stresses caused by mechanical loads
in the slot holes and to reduce the residual thermal stresses due
to the curing cycle (thermal loads).
In this case, the fixed parameters of the model were:
- Object length and external diameter;
- Type of loads and amplitude.

Fig. 2: Example of a product made with an optimization approach

- Instead, the parameters were:
- Geometry (internal diameter, slot hole radius, mutual distance
of the slot holes, etc.);
- Stacking sequence and materials.
The object's function was to reduce the product cost related to
the materials while keeping a certain failure index as a boundary
condition.

Conclusions
With isotropic materials (metals), the optimization strategy has
been used in the design stage for years. In this case, the only parameters that can be optimized usually concern geometry, such
as topological optimization.
With composite materials, the optimization approach is a more
general case of the strategy used in isotropic materials. The only
things that change are the presence of new variables/parameters such as the stacking sequence and the type of materials
used. This is due to the orthotropy of fibre-reinforced composite materials.
These new variables create much more complex models, problems and simulations, but at the same time open the doors to
new solutions impossible to find with common materials and
with classic design approaches.
The optimization design approach will soon become the new
reference strategy for companies that produce composite objects, for any application including sports, aerospace and automotive.

N°135 July - August 2020

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JEC COMPOSITES MAGAZINE - Issue #135 - July/August 2020

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