Characteristic value-based design system of shape memory springs

SMA are thermosensitive materials that change their geometry depending on the temperatures and further show elastic properties in certain temperature ranges. Due to these characteristics, springs made of SMA are of particular importance, as large forces and strokes can be realized at precise switching temperatures as well as large reversible expansions. In particular, the self-sufficient mode of operation, i.e. activation by the ambient medium, predestines SMA springs for self-regulating applications, for example in the field of thermal management. However, the development of SMA springs is a complex iterative process, as there is currently neither a suitable design system nor standardized methods for determining the required material properties due to the complex material behaviour. The resulting costs and development times hinder their widespread use in suitable industrial applications.

In order to provide companies an easier access to this technology, a design system suitable for industrial use has been developed. The basis is formed by finite element models (FE models) of SMA coil springs, the positioning behavior of those springs was simulated as a function of geometry and alloy parameters and validated on manufactured SMA springs. In this way, numerous force-stroke curves for SMA springs can be generated according to the alloy and geometry parameters. This serves as the basis for a design-of-experiment model that maps these relationships in mathematical equations. The equations are integrated into a graphical user interface that enables users to dimension SMA springs in a similar way to conventional steel springs without any knowledge of simulation methods.