Anhysteretic Magneto-Elastic Behaviour of Terfenol-D: Experiments, Multiscale Modelling and Analytical Formulas.

Giant magnetostrictive materials such as Terfenol-D and Galfenol are used to design actuators and sensors, converting magnetic input into a mechanical response, or conversely, mechanical input into a magnetic signal. Under standard operating conditions, these materials are subjected to stress. It is therefore important to be able to measure, understand and describe their magneto-mechanical behaviour under stress. In this paper, a comprehensive characterisation of the anhysteretic magneto-mechanical behaviour of Terfenol-D was performed. An energy-based multiscale approach was applied to model this behaviour. Finally, it was shown that the strain behaviour of Terfenol-D can be satisfactorily described using an analytical model derived from the full multiscale approach.

Theoretical and experimental study of the electroacoustic behavior of lithium niobate under an initial mechanical stress.

Recently, a second-order formalism of piezoelectric structures under an external mechanical stress was developed. Because the yield strength of lithium niobate was unknown, this study was not able to describe and evaluate realistic benefits of a prestress load on electromechanical properties. Therefore, in this study, experimental determination of the yield strength of lithium niobate sample is performed and shows that this limit is close to 110 MPa. Then, the nonlinearities and evolutions of electroacoustic parameters of this piezoelectric material under mechanical stress are numerically studied. By varying the initial prestress, as well as azimuthal and elevation angles, the cut planes in which a prestress induces significant benefits on velocities and coupling coefficient are identified. Finally, approximate relations describing changes between electroacoustic parameters defined in the two coordinate systems of the study are determined.