Experimental characterization and modeling of a three-variant magnetic shape memory alloy

Abstract

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.

The effect of magnetic field orientation on the open-circuit voltage of Ni–Mn–Ga based power harvesters

“…Additional discrepancies between the theoretical and experimentally observed average output voltage may be because we do not account for changes in H in our theoretical calculations. Feigenbaum et al (2016) measure approximately 20% higher field when the easy axis is aligned with the field as compared to when the hard axis is aligned with the external field. This change in H is due to change in demagnetization.…”

“…We have seen this asymmetry in the Ni-Mn-Ga MSMAs before. In order to fit experimental data, both LaMaster et al (2014) and Feigenbaum et al (2016) proposed models with asymmetric hardening functions, which suggested that the material behaves differently when going from V 1 to V 2 than viceversa. This asymmetry is still not well understood, but is confirmed by the data in this work.…”

Traveling surface undulation on a Ni–Mn–Ga single crystal element

“…Surface constraints can be created by surface treatments and external forces, including fixturing and the Maxwell force which attracts the ferromagnetic element to the magnet. The actuation mechanism of the MSM element is thus complex [29,30].…”

Demagnetizing field in single crystal ferromagnetic shape memory alloys

“…When the material is placed in a magnetic field, the magnetization vectors begin to rotate to align with the external field to minimize the potential energy of the material. However, the magnetization vectors are relatively difficult to rotate in MSMAs [4][5][6]. As a consequence, magnetic fields of adequate strength will cause the variants to reorient in order to more efficiently align the internal magnetization vectors with the external field [6,7] (figure 2 right, bottom).…”

“…Many researchers have attempted to do this (e.g. [4,7,[10][11][12][13][14][15][16]) however, there is lack of clarity in the literature regarding how to account for the material's demagnetization, both experimentally and in models.…”