On a high-potential variable-stiffness device

There are great efforts in developing effective composite structures for lightweight constructions for nearly every field of engineering. This concerns for example aeronautics, but also automotive industry and energy harvesting applications. Modern concepts of lightweight components try to use structures with adjustable properties. 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-in particular their flexural stiffness-by more than one order of magnitude. These structures use a multi-layer approach consisting of a ten-layer stack of 0.75 mm thick polycarbonate layers. The set-up is analytically described and its mechanical behavior is predicted by finite element analysis performed with ABAQUS. The individual layers are braided together by an array of shape memory alloy wires, which can be activated either all together or independently. Depending on the temperature applied by an electrical current flowing through the wires and the corresponding contraction, the wires can control the area moment of inertia of the whole stack, and with it the bending stiffness. First experimental investigations have shown a maximum stiffness change by a factor of 60, which is close to the theoretically predicted value.