Inve~tigation~oThf ermo-Mechanical Characteristics of Thin Shape Memory Alloy (Ni-Ti) Wires

It is well known that SMA's exhibit complex non linear thermo -mechanical behavior. Further they exhibit hysteresis both in the thermal and stress loading domains. It is in this context that the thermo-mechanical investigations in relation to the consistent and repeatable actuator properties assume importance. The investigations cover both quasi static and limited long term stability behavior. These are in relation to three wire diameters viz; 0.148, 0.25 and 0.364 mm respectively. The subtleties\ud of SMA behavior such as two way memory have been well captured. The implications of the 2 way effect\ud on the design has been brought out. The transformation constants obtained from the stress temperature\ud plots are covered in this study. The comparison of 'as received' wire and long term cycled wire is also\ud presented. The effect of partial strain excursions on the global behavior has been brought out. Some insight into the possible design envelope for the SMA actuator is also presented. Stable and repeatable actuator properties have been observed. The required inputs for modeling the SMA behavior have been generated. Some limited tests concerning the effect of strain rate on the tensile behavior have also been undertaken. The investigations reveal good thermo-mechanical actuator properties