Magnetomechanical characterization and unified energy model for the quasistatic behaviorof ferromagnetic shape memory Ni–Mn–Ga**This work was performed by the authors at The Ohio State University.

Abstract

This paper presents an overview of the characterization and modeling of single crystalferromagnetic shape memory Ni–Mn–Ga. A continuum thermodynamics model is presentedwhich describes the magnetomechanical characterization of single crystal Ni–Mn–Ga for thefollowing behavior: (i) sensing effect; (ii) actuation effect; (iii) blocked force (stressgeneration). The thermodynamic potentials, namely the magnetic Gibbs energy and theGibbs energy, are obtained from the Helmholtz energy in order to arrive at the set ofrequired independent and dependent variables; the potentials include magnetic energyconsisting of Zeeman, magnetostatic and anisotropy components, and mechanical energyconsisting of elastic and twinning components. Mechanical dissipation and themicrostructure of Ni–Mn–Ga are incorporated in the continuum model through theinternal state variables volume fraction, domain fraction, and magnetization rotationangle. The constitutive response of the material is obtained by restricting theprocess through the second law of thermodynamics. The model requires only sevenparameters identified from two simple experiments. Several interesting characteristics ofNi–Mn–Ga are examined in concert with the magnetomechanical characterization.