Abstract FR:

Ferromagnetic Shape Memory Alloys (FSMA) are promising candidates for sensors and actuators for their high-frequency response and large reversible strain. The aim of this dissertation is the analysis of the magneto-mechanical behaviors of FSMA. In this aim, we study, both experimentally and theoretically, the martensite reorientation in FSMA. Firstly, a 2D/3D magneto-mechanical energy analysis is proposed and incorporated into phase diagrams for a graphic study of path-dependent martensite reorientation in FSMA under 3D loadings. Criteria and material requirements for obtaining reversible strain in cyclic loadings are derived. The energy analysis predicts that FSMA in 2D/3D configurations (multi-axial stresses) has much more advantages than in 1D configuration, e. G. , higher output stress and more application flexibility. Secondly, to validate the predictions of the energy analysis, 2D experiments are performed on FSMA and results reveal that the intrinsic dissipation and the transformation strain due to martensite reorientation are constant in all tested 2D stress states. Moreover, preliminary results validate that the output stress of FSMA in 2D configuration (magnetic field with biaxial stresses) is larger than in 1D configuration, and the output stress can be increased by increasing the auxiliary stress. Finally, to predict the magneto-mechanical behaviors of FSMA in general multi-axial loadings, a 3D constitutive model is developed within the framework of thermodynamics of irreversible processes. All the martensite variants are considered and the temperature effect is also taken into account. Model simulations agree well with all the existing 1D/2D experiments. The model is further incorporated into finite element analysis for studying the non-linear bending behaviors of FSMA beams. The sample-geometry effect and the material anisotropic effect are systematically investigated.