TIPS AND TRICKS FOR CHARACTERIZING SHAPE MEMORY ALLOY WIRE: PART 3-LOCALIZATION AND PROPAGATION PHENOMENA

The mechanical instabilities in shape memory alloys (SMA) wires NiTi during superelastic behavior was studied. An experiment performed with this new setup showed that at 24°C a nucleation of M+ was accompanied by a stress drop, and a nucleation of A by a stress rise of 77 MPa. In experiments without a specialized setup such as this, these dynamic localization events are either diminished or even fully suppressed, and the true material behavior masked. By repeating the same experiment across a range of superelastic temperatures, it was able to create a more detailed phase diagram showing how nucleation stresses are strongly coupled to temperature, just like the propagation stresses. It was observed that transformation fronts occur only in relatively virgin NiTi under uniaxial loading, neither in other SMAs nor in NiTi subjected to more complex stress states or even uniaxial compression.