Design and rapid prototyping of a SMA based actuator

Materials, especially in the field of structures engineering, have always been studied and analysed by their mechanical properties. Even today, the behaviour of the main building materials such as steel, concrete and wood is described through stiffness, yield strain, fracture stress et cetera; given a material, it is supposed to passively and indiscriminately react to external inputs. Despite the fact that this classical approach to the study of materials is the most common approach, new and more sophisticated material draw attention to its lacks: these materials could be designed in order to react differently in base of the kind and magnitude of external stimuli.
This work will mainly focus on Shape Memory Alloys (SMA); these materials man-age to drastically change their behaviour according to temperature. The peculiar capacity of these materials has made them very interesting in the field of actuators as they are able to produce large motion in low volumes without the use of mechanical components. In this thesis, classical SMA’s constitutive models will be investigated, after which will be performed the numerical analysis of a real SMA-based micro- actuator through a commercial Finite Element Method (FEM) software(Abaqus).
These analysis will support the effective project and construction of a large-scaled prototype of an actuator by a 3D printer in order to test how these simulations can predict the real behaviour of the actuator.
The world of Shape Memory Alloys seems to be little inherent to structural en-gineering; however one of this thesis goals is to understand the great potential of these materials and how they can contribute in the evolution of structures by giving the possibility to really interact with users and their needs and not only provide a mechanical performance.

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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

Tesi di Laurea Magistrale

Facoltà: Ingegneria

Autore: Luca Marioni Contatta »

Composta da 121 pagine.

 

Questa tesi ha raggiunto 100 click dal 22/10/2014.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.