Design and development of advanced SMA actuators

Applications of the superelastic effect of shape memory materials are well-established and understood in the manufacture of engineering devices with adaptive properties. Conversely, exploitation of the shape memory effect for building solid-state actuators is still characterized by a trial-and-error approach. Although the thermomechanical phenomena behind the behavior of shape memory alloys (SMAs) are theoretically well-known, there is an open challenge for engineering methods to help the designer capitalize on these alloys to develop smart devices. This chapter describes research aimed at identifying simple but effective design rules for SMA-based actuators and motors, linear and rotary. The presentation concentrates on the development of SMA devices, which try to overcome the stroke limitations of conventional actuators without compromising with the force generated. It will be shown that the class of passive mechanical springs can be fruitfully turned into intelligent high-performance devices upon replacement of the material with an SMA. Alternatively, widely available SMA wires can be used smartly in compact designs with unconventional architecture. The basic theoretical model behind the design of unconventional devices will be addressed, together with laboratory prototypes demonstrating the feasibility of all of the concepts explored.