There are great efforts in developing effective composite structures for lightweight constructions
for nearly every field of engineering. This concerns for example aeronautics and spacecrafts, but
also automotive industry and energy harvesting applications. Modern concepts of lightweight
components try to make use of structures with properties which can be adjusted in a controllable
was. However, classic composite materials can only slightly adapt to varying environmental
conditions because most materials, like carbon or glass-fiber composites show properties which
are time-constant and not changeable.
This contribution describes the development, the potential and the limitations of novel smart,
self-controlling structures which can change their mechanical properties - e.g. their flexural
stiffness - by more then one order of magnitude. These structures use a multi-layer approach
with a 10-layer stack of 0.75 mm thick polycarbonate.
The set-up is analytically described and its mechanical behavior is predicted by finite element
analysis done with ABAQUS.
The layers are braided together by an array of shape memory alloy (SMA) wires, which can be
activated independently. Depending on the temperature applied by the electrical current flowing
through the wires and the corresponding contraction the wires can tightly clamp the layers so
that they cannot slide against each other due to friction forces. In this case the multilayer acts
as rigid beam with high stiffness. If the friction-induced shear stress is smaller than a certain
threshold, then the layers can slide over each other and the multilayer becomes compliant under
The friction forces between the layers and, hence, the stiffness of the beam is controlled by the
electrical current through the wires. The more separate parts of SMA wires the structure has
the larger is the number of steps of stiffness changes of the flexural beam.