Modeling and Experiments for Deformation Under Load in Ni-Mn-Ga Ferromagnetic Shape Memory Alloy

A simple model is proposed to relate strain, stress, field and anisotropy in a ferromagnetic shape memory alloy (FSMA) and experiments were performed to test the validity of the model. The model is presented as applied to the case of orthogonal field and load in a NiMn-Ga FSMA. The model predicts threshold-type strain behavior as field changes at constant load or as load changes with constant field. The measured behavior of strain with stress at constant field approximated the predictions of the model. Field-induced strain remained constant at about 6% with the addition of stress until such a stress was applied that the mechanical energy overcame the anisotropy of the sample and the strain was reduced to 0. The model's predictions of critical strain behavior with applied field at constant stress were qualitatively accurate at some stress levels, but under-predicted the field necessary to produce strain.