A theoretical model of martensitic transformations in magnetic shape memory alloys: Model formulation and variant reorientation

A model for studying the martensitic variant pattern in ferromagnetic shape memory alloys (FSMAs) and its evolution is developed. In a departure from prior work, the model allows for complete three-dimensional description of the second-order phase transformations in FSMAs under multiaxial loading. The magnetic and crystallographic aspects of the twin boundary motion responsible for this phenomenon are described. Closed-form expressions for the twin boundary velocity and overall macro displacements are derived. Nucleation of variants and propagation of twin boundaries are investigated under combined magneto-mechanical loading and compared to recent experiments. The developed model is successfully used to predict the response of three-dimensional single crystal systems.