Characterization and Modeling of Dynamic Sensing Behavior in Ferromagnetic Shape Memory Alloys

This paper is focused on the characterization and modeling of a commercial Ni-Mn-Ga alloy for use as a dynamic deformation sensor. The flux density is experimentally determined as a function of cyclic strain loading at frequencies from 0.2 Hz to 160 Hz. With increasing frequency, the stress-strain response remains almost unchanged whereas the flux density-strain response shows increasing hysteresis. This behavior indicates that twin-variant reorientation occurs in concert with the mechanical loading, whereas the rotation of magnetization vectors occurs with a delay as the loading frequency increases. The increasing hysteresis in magnetization must be considered when utilizing the material in dynamic sensing applications. A modeling strategy is developed which incorporates magnetic diffusion and a linear constitutive equation.