The dependence of coupling coefficient (k) and elastic moduli (EH and EB) on particle size and volume fraction of Terfenol powder in polymer-bonded composites has been investigated. Materials were prepared with powder in five size ranges between 106 and 710 μm and in three volume fractions (VF). The moduli show a ΔE effect, which is negative for small bias fields and positive for larger fields. EH is found to be independent of particle size and to vary with VF in agreement with model predictions. The maximum value of k, for each sample, is found to be independent of both particle size and VF and a simple model is presented which predicts this behavior and indicates that the low values of kmax arise mainly from the low modulus of the epoxy binder.
Eddy-current loss is the principal limitation to the use of Terfenol for high frequency applications. Polymer-bonded Terfenol composites, with reduced eddy current loss, aim to complement conventional Terfenol by broadening the useful range of application into the ultrasonic regime. The dependence of the static magnetomechanical properties of the composite material, on the composition parameters of particle size (Ps) and volume fraction of Terfenol (Vf) are investigated as functions of applied field and stress bias. At zero stress bias magnetisation (M) is independent of Ps and directly proportional to V f It is found that magnetostriction (λ) and differential strain coefficient (d) are both independent of V f and Ps, with saturation strains being higher then the values predicted from the simple dilution model. These higher than expected values are explained by particle connectivity within the microstructure. When stress-bias up to 20 MPa is applied to the material, the average increase in saturation strain is 28%. Normalised plots of λ versus M indicate that the magnetisation process within the material consists of both domain wall motion and rotatio
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