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Researchers have attempted to characterize and predict the magneto-mechanical behavior of magnetic shape memory alloys (MSMAs) for over a decade. However, all prior experimental investigations on MSMA have been performed on samples accommodating two martensite variants and generally the MSMA is only exposed to two-dimensional magneto-mechanical loading. As efforts have been underway to develop models able to predict the most general (i.e. 3D) loading conditions for MSMAs with three-varints, there is also a need for experimental data to support the calibration and validation of these models. This paper presents magneto-mechanical data from experiments where MSMA specimens, whose microstructure accommodates three martensite variants, is subjected to three-dimensional magneto-mechanical loading, along with model predictions of these experimental results. The 3D magneto-mechanical model deployed here is a modified version of the model developed by our group (LaMaster et al 2015 J. Intell. Mater. Syst. Struct. 26 663-79), and assumes that three martensite variants coexist in the material. The LaMaster et al model captures some of the general trends seen in the experimental data, but does not predict the data with a high degree of accuracy. Possible reasons for the mismatch between experimental data and model predictions are discussed.

Researchers have attempted to model the magneto-mechanical behavior of magnetic shape memory alloys (MSMAs) for over a decade, but all of the models developed to date have only been validated against experimental data generated under two-dimensional loading conditions. As efforts have been underway to develop models able to predict the most general (i.e. 3D) loading conditions for the material, there is a need for experimental data to support the calibration and validation of these models. This paper presents magneto-mechanical data from experiments where a MSMA specimen whose microstructure accommodates three martensite variants is subjected to three-dimensional magneto-mechanical loading. To the best of our knowledge, all prior experimental investigations on MSMA have been performed on samples accommodating two martensite variants and exposed to two-dimensional magneto-mechanical loads. The experimental results from the 3D loading of the three variant MSMA specimen are used to calibrate and validate a 3D model developed by this group [LaMaster et al. (2014)]. This model assumes that three martensite variants coexist in the material. The LaMaster et al. model captures the general trends seen in the experimental data, but does not predict the data with a high degree of accuracy. Possible reasons for the mismatch between experimental data and model predictions are discussed.

Magnetic shape memory alloys are a relatively new class of materials that are suitable for actuation, sensing, and power harvesting. The power harvesting capability comes from the change in magnetization that the material exhibits when internal martensitic variants change orientation. In typical power harvesting tests, the material is loaded with axial compression in the presence of a bias magnetic field applied normal to the compressive loading direction. However, previous results suggest that having a component of the bias magnetic field applied axially, parallel to the compressive stress, can increase the power output of MSMAs. Furthermore, most of the MSMAs power harvesting results reported to date focused on the open circuit voltage that the material can generate during cyclic loading. However, this information is not indicative of the true power harvesting capability of the material and one has to focus on the power output of the material instead. This paper presents voltage trends and power output data for a MSMA sample exposed simultaneously to a cyclic compressive stress and bi-axial magnetic field.

Magnetic shape memory alloys (MSMAs) are materials commonly used for actuation, sensing, and/or power harvesting applications. While the actuation response of MSMAs can be fairly accurately predicted by currently available constitutive models, the power harvesting and/or sensing performance is not predicted as well. This suggests that current models lack features related to the change in magnetization. One such feature that is known to exist, but is not present in any current model, is the natural offset of the magnetic easy axis from the short axis of the tetragonal martensitic unit cell of MSMAs. Experimentally, Scheerbaum et al. [1] observed that this offset angle is in the range of 2° to 6°. While this is a relatively small angle, it is expected to make a dramatic difference in the evaluation of the power harvesting output, as it creates favorable domains even when the field is applied perpendicular to the short axis of the unit cell. Therefore, to facilitate the design of MSMA based sensing and power harvesting devices, a continuum model for the magneto-mechanical response of MSMAs, that accounts for the magnetic easy axis offset from the short side of the unit cell is derived from thermodynamic requirements and evaluated in this work.