DETWINNING OF THE MARTENSITE PHASE IN SHAPE MEMORY ALLOYS (SMAs) AND THE INFLUENCE OF PRESTRESS IN SMA ACTUATORS

Abstract

The unique characteristic, Shape Memory Effect (SME), of Shape Memory Alloys (SMAs), is primarily investigated by researchers as an economical source of actuation supplemented by its simple operating principle, and elimination of moving parts. Depending upon whether the SMA wire is martensitic, in transition, or austenitic phase, it exhibits different elastic isothermal behaviour. The microstructure is altered by the stress and thermal levels at both the low temperature phase and the high temperature phase. Precise experimental results for the isothermal measurements in the detwinning of the martensite phase of Nitinol and the influence of prestress in the performance of SMA wire actuators is presented in this study. Force of actuation and the displacement due to contraction during quazi-static actuation (transformation) and its dominance are illustrated for Nitinol wires used in SMA actuators.