Thermo-Magneto-Mechanical Coupling Dynamic Behavior of Ferromagnetic Shape Memory Alloys

Ferromagnetic Shape Memory Alloy (FSMA) is a better candidate for high-frequency actuators (1Hz-1000 Hz), compared with traditional SMA, as it can provide large recoverable deformation controlled by fast-changing magnetic fields. One of the difficulties in promoting the material’s application is the lack of grasp on its dynamic behaviors accompanied with the sophisticated coupling of mechanical, magnetic and thermal quantities.  In our study, systematic experiments on the dynamic behaviors have been conducted by various magneto-mechanical loadings (with different frequencies/magnitudes of magnetic fields and stresses), while the mechanical deformation/stress, temperature, and applied magnetic fields were monitored simultaneously. It was found that the material’s performance was significantly influenced by the temperature change caused by the mechanical dissipation and the magnetic dissipation (eddy current generated in the material by the fast-changing magnetic fields). The experiments also showed that there is a resonant frequency where the largest reversible cyclic strain/deformation can be achieved; and the resonant frequency depends on the setting (the system’s stiffness, the level of pre-stress on the samples, etc.). Based on the experiments, simple models are developed to describe the relations between the thermo-magneto-mechanical quantities and provide guidelines for setting the system to optimize the dynamic performance.