An Anisotropic Microscopic Thermodynamic Model And Magneto-Mechanical Coupling Behavior Of NiMnGa Alloy

As a new kind of smart actuator and sensor materials, ferromagnetic shape memory alloy (FSMA) can provide the magnetic shape memory effect, huge output strains and high response frequencies. The magnetic smart materials have attracted more researchers’ interests in these recent years, and have the important applications in national defense, aerospace’s smart structures devices and control systems.Firstly, a microscopic thermodynamic model for describing martensitic variants rearrangement in FSMAs was proposed, which is based on the Eshelby equivalent inclusion method, the Mori-Tanaka averaged scheme and the thermodynamic theory. The analyses of the magneto-mechanical coupling behavior of ferromagnetic shape memory alloys in different directions of applied magnetic field and stress were performed. In the modeling, the anisotropy of the martensitic variants of ferromagnetic shape memory alloy were considered. By means of choosing some proper internal variables, a thermal kinetic equation to describe the martensitic variants rearrangement was developed.Secondly, we analyzed the martensitic variants rearrangement and the magneto-mechanical coupling behavior of ferromagnetic shape memory alloy in the applied magnetic field and the stress orthogonal and collinear, respectively. The influence of anisotropy and inclusion morphology of martensite variants on magnetic field induced strain and stress-strain behavior were considered and discussed in detail. The predictions of theoretical model show the good agreement with the experimental data. The results show that the magneto-mechanical coupling behavior of ferromagnetic shape memory alloy influenced by the magnetization rotation and the martensitic variants characteristics (anisotropic and inclusion morphology, etc.). The martensitic variants rearrangement and the magneto-mechanical coupling responses were revealed by the present thermodynamic model to show good agreement with the experimental observations for the collinear case of the applied magnetic field and stress.