Huge Magnetostriction of Magneto-rheological composite ; Magnetostriction gigantesque de composite Magneto-rheologique

This thesis is aimed to measure and explain the elongation of M.R.E. placed in a homogenous magnetic field. M.R.E. is material consisting in ferromagnetic particles embedded in an elastic matrix. Combination of a silicone, with low elastic modulus (E0=0.14 MPa), and Iron particles, characterized by a high saturate magnetization (µ0Msat=2.14 T), allows large deformation (some percents) when placed in the applied field µ0H0=1.2 T. Coupling of the dipolar forces calculation between the particles, randomly distributed in a cylinder-shape volume, with strain calculus, using F.E.M. software, is a good agreement with a magnetostrictive experiment. Magnetized sample get a so-called “demagnetizing” energy bounded to it shape: “flatter” samples yields to a larger demagnetizing energy than longer ones. Composite magnetization has been investigated in this thesis through 2 parameters: the saturate magnetization and the effective demagnetizing coefficient. Experiments, carried on samples with different shapes, show the effect of the demagnetizing energy, flattest sample (with aspect ratio c/a =0.3) exhibits the largest strain of 10%. A model, based on the competition of the demagnetizing energy and elastic energy, during the strain, accounts for this shape effect. That model also deals with the filling factor impact on the strain. An optimal filling factor of 27% has been measured and predicted. Magnetostriction of composites with hard magnetic particles was investigated as function of the applied field. Due to the magnetization hysteresis loop of those particles, a “memory effect” was found in the magnetostriction. Finally, elastic modulus and particle magnetization are both temperature dependent. The temperature behavior of the magnetostriction is measured. By tuning these parameters, materials with different temperature behavior could be designed. ; Le but de cette thèse est l'étude expérimentale et théorique de l'élongation de M.R.E. (Magneto Rheological Elastomer) placé dans un champ magnétique homogène. Ces matériaux ...