JEC COMPOSITES MAGAZINE - Issue #94 - January/February 2015 - 55

has led to the common design methodology that produces what is known
in industry as "black metal". With this
method, the black carbon fibre laminate
layers are designed with quasi-isotropic
material properties and constant thickness sections which really eliminate
most of the additional variables available
for the designer. Here, the only non-isotropic material property is the throughthickness direction and as long as the
structure is primarily loaded in-plane,
the designer just has to worry about how
thick to make the laminate and its shape,
reducing the problem to simply shape
and thickness variables, the same as with
metals. This makes the designer's job
more manageable but the downside of
this is that many of the unique properties of composites are not really utilized.
The designer is simply taking advantage
of the reduced weight of the material
and nothing else.

Fig. 3: Ply shape definition in HyperMesh close to the manufacturing process

Fig. 2: More detailed picture showing the
composites optimization approach in OptiStruct

the human mind and computers are required to achieve success. Modifications
to existing structural optimization
methods had to be developed to address
some of the unique design considerations of composites such as ply shape,
ply orientation, stacking sequence, and
the considerations of composite manufacturing constraints.

Design optimization

This is where the use of advanced
analysis tools is particularly important.
Computer-based analysis tools, such
as finite element analysis, are able to
analyse the effects of the many variables
in a more efficient manner to provide
the designer and the analyst with more
information to make better design
decisions. Mathematical optimization
methods can bring added value to the
analysis process by using the power
of the computer to cycle through the
many variables available and optimizing
the structure to better utilize the many
unique properties composites bring to
the design.

The large number of design variables
available for composites also causes
problems on the testing side. For metal
structures, a few simple tests can suffice to acquire the necessary material
properties for the design. For laminate
composites, tests need to be conducted
on the laminate designs used and since
an infinite number of laminate designs
are possible, the testing can also be
an infinite exercise. As a result, most
manufacturers stick to designs based
on the available material data which are
generally quasi-isotropic configurations.
This is another area where design and
analysis can provide great benefits to
this industry. Many design and material configurations can be analysed and
optimized on the computer and then
testing is simply required on the chosen
configuration. The selection process
occurs virtually, which can save an organization a tremendous amount of time
and money. As confidence grows in the
analysis methods, the amount of physical testing required will go down.

Failure modes

Optimization technology is an excellent
method to efficiently and effectively deal
with the many design variables present
with composite structures. Designers of
metal structures can often get away with
simple calculations to develop a suitable
design but with composite structures,
the number of variables is too great for

A challenge with the analysis of composites is that the failure modes are
often quite different than with metals.
For metals, failure generally occurs
through crack growth and corrosion.
For composites, there are a number of
failure modes including delamination,
matrix cracking, fibre breakage, thermal

Fortunately, numerical optimization
methods are available now that can
help designers sort through all of the
variables and get to an optimized design
in terms of weight and performance.
As more experience is gained in using
these methods, the weight of airplanes
and automobiles can be further reduced.
In addition, the results can produce a
geometry that is difficult to manufacture
using traditional methods but with the
advent of additive layered manufacturing (ALM) or 3D printing methods,
the future offers the prospect of making
components that are truly optimized,
much like we see in nature.

No94 January - February 2015 /

jec composites magazine 55

JEC COMPOSITES MAGAZINE - Issue #94 - January/February 2015

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #94 - January/February 2015