Design and rapid prototyping of a SMA based actuator

List of Tables From a mechanical to a functional design approach Materials have always been dened by their mechanical properties. Even today, structural engineering carries in this cultural approach: just think that the main structural materials such as steel, concrete, masonry, wood et cetera are described through mechanical parameters as stiness, ductility, yield and fracture strain. Nev- ertheless, research in materials has produced lots of sophisticated and advanced ma- terials able not only to passively and indiscriminately react to external stimuli, but also to interact "intelligently" with the external world. Among these materials we can nd a large variety of properties, for example piezoelectric materials manage to product electric potential when deformed, PH-sensitive materials are able to change in volume and colour accordingly to the environment’s PH, acoustic materials prod- uct noise when deformed over a threshold, and so on. In addition of these, exist the material considered in this thesis, the shape memory alloys, that change their shape and mechanical properties accordingly to their temperature. The approach to the material has therefore become more complex: the material is no more called to just ensure a mechanical performance, but to perform a function. It’s important to point up that even in the classical approach to design a certain function was needed, but was carried out by the structural element or by a set of mechanical components, while with the functional design approach is the material itself to be designed in order to carry out its function without any other mechanical element. Thanks to the capacity of these materials to react dierently according to the environment, engineers have the possibility to re-invent the classical mechanical and structural elements because the function they were used to carry out can be achieved in an easier way employing intelligent materials. This is the spirit of SMA- based actuators: as will be extensively discussed in 2, they employ the capacity of shape memory alloys to produce hight displacements in low volumes if correctly actuated without mechanical elements in order to get a more simple and durable actuation system. 19