Tips and Tricks for Characterizing Shape Memory Alloy Wire: Part 2—fundamental Isothermal Responses

T his is the second in a series of articles to introduce phenomena and experimental subtleties that can lead to difficulties in testing shape memory alloy (SMA) wire. Our aims were to acquaint uninitiated engineers with SMA testing and to highlight pitfalls in technique and interpreting test results. In the previous article (Part 1), thermomechanical experiments were presented on two commercial Nitinol alloys: a shape memory (SM) wire, having an austenite finish temperature, Af, above room temperature, and a superelastic (SE) wire, having an Af below room temperature. Both SM and SE behavior were demonstrated for each in different temperature regimes along with a description of the underlying microstructural mechanisms responsible for these unusual behaviors. Differential scanning calorimetry (DSC) thermograms were provided for each alloy as a first step to quantify their transformation temperatures, specific heats, and latent heats of transformation.