Shape Memory Alloy actuators are designed to activate smart structures supplying force or displacement. Generally, the ON/OFF configuration is used, that is to say that the SMA element transforms completely when heated, expressing at once the maximum force/displacement for which it was designed. The variable displacement and force are obtained through a so-called Shape Memory Alloy tunable actuator. Usually, to acquire this capability, the complex actuating system relies on multi-actuators assembled in parallel or series configuration. But these configurations increase the complexity and cost of the system. The aim of this work is to develop a Shape Memory Alloy tunable actuator by means of partial austenitic transformation. The transformation of SMA in actuators is usually achieved by Joule heating, supplying enough power to exceed austenitic finish temperature. Fine control of the electric power, managed either through voltage or current, can allow a similar control of the degree of transformation and therefore of the level of force/displacement generated. This also facilitates the control of the Shape Memory Alloy tunable actuator. With these developments, the desired variable response is acquired. To realize the final aim of this project, a Shape Memory Alloy actuator, in particular, Nitinol wire, is examined in detail. In the first part of work, the material thermo-mechanical characterization is done through Differential Scanning Calorimetry (DSC) and Isothermal Tensile Test. Then, another important part is devoted characterizing partial transformations. To achieve this characterization, a new experimental setup is developed with respect to the one used in previous works, considering previous limitations in the experiment. Then, to characterize tunable actuators and to obtain phase diagram for different loads, the analyses are examined against different weights. Lastly, to prove the tunability of the actuator, the results of the previous characterization are used to control a morphing structure.
Gli attuatori basati su leghe a memoria di forma (SMA) sono progettati per azionare strutture smart fornendo forza o spostamento. Generalmente, viene utilizzata la configurazione ON / OFF, cioè l'elemento SMA viene scaldato fino a completa trasformazione, esprimendo direttamente la massima forza/spostamento per cui è stato progettato. Lo spostamento e la forza variabili possono essere ottenuti tramite un attuatore modulabile. Di solito, per acquisire questa capacità, il complesso sistema di azionamento si basa su multi-attuatori assemblati che lavorano in parallelo o in serie. Ma queste configurazioni aumentano la complessità e il costo del sistema. L'obiettivo di questo lavoro è sviluppare un attuatore modulabile in lega di memoria di forma mediante trasformazione austenitica parziale. La trasformazione delle SMA negli attuatori è solitamente ottenuta con il riscaldamento per effetto Joule, fornendo una potenza sufficiente per superare la temperatura di fine trasformazione austenitica. Il controllo fine della potenza elettrica, gestito tramite tensione o corrente, può consentire un controllo simile del grado di trasformazione e quindi del livello di forza/spostamento generato. Ciò facilita anche il controllo dell'attuatore modulabile. Con questi sviluppi, viene acquisita la risposta variabile desiderata. Per realizzare l'obiettivo finale di questo progetto, attuatori a memoria di forma (fili in NiTinol) sono stati esaminati in dettaglio. Innanzitutto, la caratterizzazione termomeccanica del materiale è stata effettuata attraverso un'analisi calorimetrica a scansione differenziale (DSC) e test di trazione isotermici. Un’altra parte importante è dedicata a caratterizzare le trasformazioni parziali. Per ottenere questa caratterizzazione, è stata sviluppata una configurazione sperimentale rinnovata rispetto ai lavori precedenti e migliorata considerando le precedenti limitazioni nell'esperimento. Quindi, per caratterizzare gli attuatori regolabili e ottenere il diagramma di fase per carichi diversi, le analisi vengono esaminate a fronte di pesi diversi. Infine, per dimostrare la regolabilità dell'attuatore, i risultati delle precedenti caratterizzazioni sono usati per controllare una struttura morphing.
Tunable actuators based on SMA for morphing applications : experimental characterization of partial martensitic transformations
KARACAM, GIZEM KUBRA
2017/2018
Abstract
Shape Memory Alloy actuators are designed to activate smart structures supplying force or displacement. Generally, the ON/OFF configuration is used, that is to say that the SMA element transforms completely when heated, expressing at once the maximum force/displacement for which it was designed. The variable displacement and force are obtained through a so-called Shape Memory Alloy tunable actuator. Usually, to acquire this capability, the complex actuating system relies on multi-actuators assembled in parallel or series configuration. But these configurations increase the complexity and cost of the system. The aim of this work is to develop a Shape Memory Alloy tunable actuator by means of partial austenitic transformation. The transformation of SMA in actuators is usually achieved by Joule heating, supplying enough power to exceed austenitic finish temperature. Fine control of the electric power, managed either through voltage or current, can allow a similar control of the degree of transformation and therefore of the level of force/displacement generated. This also facilitates the control of the Shape Memory Alloy tunable actuator. With these developments, the desired variable response is acquired. To realize the final aim of this project, a Shape Memory Alloy actuator, in particular, Nitinol wire, is examined in detail. In the first part of work, the material thermo-mechanical characterization is done through Differential Scanning Calorimetry (DSC) and Isothermal Tensile Test. Then, another important part is devoted characterizing partial transformations. To achieve this characterization, a new experimental setup is developed with respect to the one used in previous works, considering previous limitations in the experiment. Then, to characterize tunable actuators and to obtain phase diagram for different loads, the analyses are examined against different weights. Lastly, to prove the tunability of the actuator, the results of the previous characterization are used to control a morphing structure.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/145471