FEATURE Experimental Characterization of Active Materials Series TIPS AND TRICKS FOR CHARACTERIZING SHAPE MEMORY ALLOY WIRE: PART 4 – THERMO-MECHANICAL COUPLING

T his is the fourth paper in our series, identifying unusual phenomena and providing recommendations for the thermo-mechanical characterization of shape memory alloy (SMA) wire. Part 11 provided basic background of the martensitic transformations between austenite (A) and martensite (M) which are responsible for the shape memory (SM) effect and superelasticity (SE). Two typical NiTi SMA alloys (SM wire with austenite start temperature As > 20 ◦C and SE wire with austenite finish temperature Af < 20 ◦C) were characterized by differential scanning calorimetry (DSC) to measure transformation temperatures, specific heats, and latent heats of transformation. SM and SE were demonstrated for each alloy in their respective temperature regimes. Part 22 reviewed various methods to obtain fundamental sets of isothermal mechanical responses for the two SMA wire alloys. Part 33 highlighted the unusual phenomena of strain localization and phase front propagation that can occur during stress-induced transformations.