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[en] The basic problems of magnetostriction are reviewed. The origin of magnetostriction, elastic and magnetoelastic energies, equilibrium strains and the temperature dependence of magnetostriction are presented. The magnetostriction in the band model of ferromagnetism, paramagnetostriction as well as oscillatory magnetostriction are analysed. Finally, the experimental methods used for the study of magnetostriction coefficients are given. (author)
[en] Glass-coated micro wires are very interesting materials for theoretical study as well as for practical applications. Having positive magnetostriction, their domain structure consists of single axially magnetized domain and magnetization process runs through Large Barkhausen jump of a single domain wall along entire micro wire. This gives us possibility to study a single domain wall propagation on large scales (few cm). As a result of their complex anisotropy distribution, the glass coated micro wires exhibit very fast domain wall propagation, sometimes faster then sound speed. The domain wall dynamics can be very effectively modified by different anisotropies introduced in the wire by magnetic field, mechanical stress, thermal treatment, etc... In such a way, domain wall dynamics with the high domain wall velocity that is independent on magnetic field can be achieved. Stability of domain wall dynamics can be enhanced by using nanocrystalline compositions of micro wire that combines low anisotropy of amorphous alloys with high structural stability of crystalline materials. On the other hand, sensitivity of domain wall dynamics on external parameters can be employed in the sensoric applications. The switching field at which the single domain wall starts to propagate is strongly sensitive to the temperature, mechanical stress, frequency of applied magnetic field etc... Knowing the physical origin of such sensitivies allows us to construct miniaturized multifunctional sensor that can even be embedded into the material structure. (author)
[en] This paper proposes a systematic approach for an accurate control of the Terfenol-D actuator taking into account hysteresis, modeled by applying the classical Preisach operator with memory curve. A desired input displacement is calculated by using the hysteresis inverter, which is fed into the actuator. Then the PI compensator corrects the error between the commanded and actual displacements. Experiments with the step responses show that the PI controller settles in 70 ms and the hybrid controller in 20 ms. It means that the concurrent application of two control schemes is effective to control the actuator
[en] The magnetoelastic contributions to the elastic constants of Ho, Dy, and Tb were determined at temperatures in the paramagnetic range in applied fields up to 75 kG. Magnetization measurements were also made in order to facilitate the comparison of the experimental results with theory. Initially the results were analyzed in terms of a theory due to Southern and Goodings, but the agreement was poor. The field dependence predicted by this theory, using magnetoelastic coupling constants estimated from static magnetostriction data, was generally much smaller than the observed dependence, and, in many cases, the theory did not predict the correct qualitative field or temperature dependence. The reasons for these discrepancies are, apparently, the use by Southern and Goodings of first-order perturbation theory, together with an inappropriate application of finite-strain theory. A calculation of the magnetoelastic contribution to the elastic constants was carried out employing the molecular-field approximation, but without using perturbation theory and using only the conventional small-strain tensor. This approach, similar to that of Freyne, is in much better agreement with the experimental results
[en] The present manuscript represents the third part of a series of studies about a continuous micromagnetic model for amorphous microwires with non-uniform magnetic structure (Torrejon et al., J. Magn. Magn. Mater. 323 (2011) 283; Torrejon et al., J. Magn. Magn. Mater. 333 (2013) 144). Here we compare the predictions of this model with experiments, and show the validity of this approach when a uniform magnetic structure in the microwire cannot be considered. The analyzed microwires exhibit ultrasoft magnetic behaviour and negative magnetostriction, with a non-uniform magnetic structure composed of an axially magnetized inner core exchange-coupled with a circumferentially magnetized outer shell. The static properties were obtained by magnetometry. The high frequency response, axial permeability, was measured from a conventional single coil permeameter connected to a network analyzer. The microwave response is strongly affected by skin effect, which therefore needs to be taken into account for comparison with theory. The validity of the continuous model is proved through the experimental dependence of the permeability on axial static field. Finally, the efficient dynamic magnetization is evaluated from the imaginary component of permeability. - Highlights: • We model magnetic properties of microwires with circumferential anisotropy. • Skin effect correction has to be considered for small microwires. • Validity of model is proved by permeability dependence on axial static field. • Wires with small volume of the core can be well described by macrospin approach. • The exchange-coupled continuous core-shell model is compared to experiments
[en] A new model able to describe magnetostriction for slowly varying mechanical load is presented. The model and its pseudo-compensator exploit the formalism of the classical Preisach model and is therefore easy to implement and well behaved. Experimental results showing the encouraging performances of the approach are provided
[en] For the electromechanical actuator two piezoelectric or magnetostrictive expansion joints stretched in a frame are provided as tension and pressure generators. The lift is transmitted to a distance transformer, amplifying the lift, via joint-shaped connecting bars free from play. The distance transformer consists of a two-armed lever, on the arms of which one of the expansion joints or bending elements is acting respectively. The lever, the connecting bars, and a bearing are formed from a homogenous material e.g. by casting. With this device large lifts can be realized with high positioning frequency and high lifting accuracy. (DG)
[de]Bei dem elektromechanischen Stellglied sind zwei in einen Rahmen eingespannte piezoelektrische oder magnetostriktive Dehungskoerper als Zug- und Druckerzeuger vorgesehen. Der Hub wird ueber gelenkfoermige Verbindungsstege auf einen den Hub vergroessernden Wegtransformator uebertragen, wobei dieser aus einem zweiarmigen Hebel besteht, auf dessen Arme jeweils einer der Dehnungs- oder Biegekoerper einwirkt. Der Hebel, die Verbindungsstege und ein Lager hierfuer sind aus einem homogenen Werkstoff, z.B. durch Giessen, gebildet. Es koennen grosse Huebe mit hoher Stellfrequenz und grosser Hubgenauigkeit realisiert werden. (DG)
[en] Magnetostrictive properties of Iron-Gallium alloys, such as the saturation of magnetic induction and magnetostriction can be derived from experimental measurements. It is known that, in order to exhibit the largest saturation magnetostriction, Galfenol requires the application of a suitable external compressive stress. In order to avoid a bulky system to provide such stress, a built-in stress could be added to the material through a technological process known as stress annealing. In this paper an experimental method to evaluate the stress applied to Galfenol rods is presented. Then, the method can be exploited either to evaluate the built-in stress or to develop a stress sensor. A concept device exploiting the method and its experimental characterization are presented.
[en] A main limitation of most models describing the effect of stress on the magnetic behavior is that they are restricted to uniaxial - tensile or compressive - stress. Nevertheless, stress is multiaxial in most of industrial applications. An idea to overcome the strong limitation of models is to define a fictive uniaxial stress, the equivalent stress, that would change the magnetic behavior in a similar manner than a multiaxial stress. A first definition of equivalent stress, called the deviatoric equivalent stress, is proposed. It is based on an equivalence in magneto-elastic energy. This formulation is first derived for isotropic materials under specific assumptions. An extension to orthotropic media under disoriented magneto-mechanical loading is made. A new equivalent stress expression, called generalized equivalent stress, is then proposed. It is based on an equivalence in magnetization. Inverse identification of equivalent stress is made possible thanks to a strong simplification of the description of the material seen as an assembly of elementary magnetic domains. It is shown that this second proposal is a generalization of the deviatoric expression. Equivalent stress proposals are compared to former proposals and validated using experimental results carried out on an iron-cobalt sheet submitted to biaxial mechanical loading. These results are compared to the predictions obtained thanks to the equivalent stress formulations. The generalized equivalent stress is shown to be a tool able to foresee the magnetic behavior of a large panel of materials submitted to multiaxial stress. - Research highlights: → Classical magneto-elastic models restricted to uniaxial stress. → Stress demonstrated multiaxial in most of industrial applications. → Proposals of deviatoric and generalized equivalent stresses - multidomain modeling. → Experimental validation using iron-cobalt sheet submitted to biaxial loading. → Generalization of former proposals and modeling of previous results.