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Design of ferromagnetic shape memory alloy composites for robust and low-cost actuators under applied magnetic field gradient”

Minoru Taya (University of Washington)

Prager Medal Symposium in honor of George Weng: Micromechanics, Composites and Multifunctional Materials

Mon 9:00 - 10:30

MacMillan 117

Ferromagnetic shape memory alloys (FSMAs) have attracted a strong attention among materials scientists and actuator designers thanks to their fast-responsive and large strain capability. There are three mechanisms of actuation associated with FSMAs, under magnetic field: (i) magnetic field-induced phase transformation, (ii) martensite variant rearrangement and (iii) hybrid mechanism. The first two mechanisms are operative under constant magnetic field, while the third mechanism on gradient field. The third mechanism is based on a set of chain reactions, first applied magnetic flux(or field) gradient, magnetic force, stress induced martensite phase transformation, resulting in the phase change from stiff austenite to soft martensite phase, leading to large displacement. Based on this mechanism, we designed several FSMA and FSMA composite actuators, spring and torque. The advantages of this are large stress (hundred MPa in the case of FePd), modest – intermediate strain, fast actuation time. However, the cost of processing FSMAs such as FePd is very expensive. On the other hand, superelastic shape memory alloys have high mechanical performances, large transformation strain and stress capability. But, the speed of superelastic SMAs by changing temperature is slow. If a ferromagnetic shape memory alloy composite composed of a ferromagnetic material and a superelastic SMA can be developed and such a composite can be actuated under the above hybrid mechanism, then, new cost-effective and high-speed actuators can be designed. Several types of Ferromagnetic Shape Memory Alloy (FSMA) composites are discussed in this talk, (1) helical spring, (2) laminated composite and (3) particulate composite.