Magnetic shape memory alloys (MSMAs) are a class of materials that can exhibit up to 10% recoverable strain as a result of the application of either magnetic field or compressive stress. This unique property makes MSMAs potentially suitable for commercial applications such as sensors, power harvesters, or actuators. Before any commercial applications are fully realized, effective models capable of accurately predicting the magneto-mechanical behavior of MSMAs need to be developed. This paper builds on an existing thermodynamic based constitutive model for MSMAs by accounting for the three-dimensional nature of the demagnetization phenomenon. In particular, the importance of using a demagnetization factor that comes from a solution to the three-dimensional magneto-static boundary value problem is highlighted. Also, the magnetic field present in directions other than that applied because of demagnetization is included in the model. Finally, this work proposes a more flexible means of calibrating thermodynamic based constitutive models for MSMAs.

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Magnetic shape memory alloys (MSMAs) can exhibit the shape memory effect when there is a magnetic field in the vicinity of a material point. The microstructure of the MSMAs is comprised of tetragonal martensite variants, each with their preferred internal magnetization orientation. Starting from a random variant orientation, the application of a large enough magnetic field will cause the variants to reorient so that the internal magnetization vectors align with the external field. Then, keeping the magnetic field constant and adding a variable compressive stress in a direction normal to that of the magnetic field, some or all of the martensitic variants may rotate into a stress preferred state. As the variants reorient, the internal magnetization vectors rotate, and the material's magnetization changes. For power harvesting and sensing applications, the change in magnetization induces a current in a pickup coil placed around the MSMA specimen, resulting in an output voltage at its terminals according to Faraday's law of inductance. This paper focuses on the evaluation of the voltage output, both experimentally and numerically, in an attempt to assess the ability of a MSMA thermodynamic based constitutive model, used in conjunction with Faraday's law of induction, to predict the variant reorientation induced voltage output. Assessing the accuracy of the predicted voltage is beneficial for the design of both MSMA based power harvesting devices and MSMA based displacement sensors.