Shape Memory Alloys (SMAs) are a relatively new band of materials that have not been utilized to their fullest potential. These materials are alloys composed essentially of Nickel, and Titanium, with possible additions of Copper, Zinc and Aluminum and can recover pre-set shapes even after deformation, by heat activation. When deformed in the low temperature, these shape memory alloys rearrange themselves into 'monoclinic' lattice structures, which give them the shape of a parallelogram. This parallelogram shape converts into more orderly 'cubic' structure upon heating. The heat that is required is supplied by any hot source - hot water, DC power supply etc.
In my research, the thermo-mechanical properties of shape memory alloys are studied. Certain key relationships between the characteristic physical properties of shape memory alloys like strain and temperature are determined through experiments. These experiments lead to the determination of characteristic temperatures of shape memory alloys, which are Martensite start temperature, Martensite finish temperature, Austenite start temperature, and Austenite finish temperature. Then, using these parameters, certain existing models for shape memory alloys are verified.
The knowledge obtained from the experiments and models highlighting shape memory behavior gives enough background to design one-dimensional actuators. These actuators are designed using shape memory extension and shape memory compression springs. A stroke or travel of 0.6 inch is aimed at from these actuators. Based on this, the springs are selected and the actuators are built and tested.
The motion of these actuators are modeled for both compression and expansion processes. Experiments are carried out using load cells at various displacements of the actuators, in order to determine the force outputs at various displacements. The experimental results are compared with the models. The force-deflection curves would be expected to correlate to the stress-strain curves because force is analogous to stress and displacement, to strain. These, and other observed phenomena are explained from the point of view of shape memory alloy behavior. There has not been much research dedicated towards designing linear shape memory actuators that would be able to travel both inward and outward depending on the user input from a remote control, which is basically what this research aims to do. A detailed study has also been carried out on the force-displacement relations of these actuators and correlated with the observed behavior of shape memory alloys, which again is a novel feature of this research.
The main advantage of shape memory alloys over other smart materials is that they have a very high recoverable strain and force output. These factors contribute chiefly to various potential and existing applications. These compensate for the main disadvantages associated with SMAs, which are heat loss and high power requirements.