Ambient heat transfer effects on magnetic shape memory alloy actuators

Magnetic Shape Memory Alloy (MSMA) is a promising candidate for high-frequency large-stroke actuators applications as it is able to provide a large recoverable deformation with high-frequency magnetic-field-induced martensite reorientation. Recent experiments revealed that thermo-magneto-mechanical coupling effect needs to be considered to obtain a reliable performance of MSMA actuators. Particularly, the heat generation from the energy dissipation of the high-frequency martensite twin-boundary motions causes a temperature rise in the material, which influences the temperature-dependent martensite reorientation process and/or triggers the temperature-induced martensite-austenite phase transformation so that the output strain can be influenced significantly. Therefore, besides the usual magneto-mechanical conditions (such as the magnetic field frequency, the applied mechanical stress and the system mechanical stiffness), the ambient heat-exchange efficiency between MSMA actuator and the ambient (which counteracts the temperature rise) is important in controlling the output strain amplitude under the high-frequency magnetic actuation. In this paper, we study the strain amplitude modulation of MSMA actuator by controlling the ambient heat transfer efficiency by applying an ambient airflow (the airflow velocity can be tuned via a compressed air source). The results are helpful not only for the optimization design of the large-stroke MSMA actuators, but also for the insight into the principles of the multi-physics coupling in similar smart materials.