Further Numerical/Experimental Investigations Of Nitinol Actuator Springs

Shape memory alloys (SMAs) belong to the class of smart materials that can be found in numerous applications, e.g., for instance, aeronautical, biomedical, structural, mechanical, and earthquake engineering. Solid phase transformations induced either by stress or temperature are behind the remarkable properties of SMAs that motivate the concept of innovative smart actuators for different purposes.

SMA helicoidal springs constitute an important example of actuator employed in several applications and attract the attention of several authors. In fact, despite the apparent simplicity, the behavior of SMA helicoidal springs is rather complex and the design of such devices may possibly take advantage of numerical simulations.

The proposed contribution deals with both the numerical and experimental investigations of SMA wires and helicoidal springs, starting from the preliminary results presented by Auricchio et al. (2013). In particular, we investigate SMA wire and helicoidal spring thermo-mechanical behavior through some conducted experimental tests. Then, we use experimental results to investigate three phenomenological constitutive models able to represent SMA macroscopic behavior, i.e., the models presented by Souza et al. (1998), Auricchio et al. (2011), and Auricchio and Bonetti (2013). We discuss model constitutive equations and features, material parameters calibration process as well as finite element analyses. The comparison between numerical predictions and experimental data allows to comment and discuss several aspects about model reliability and features characterizing real SMA material behavior.