Magnetomechanical properties of epoxy-bonded Terfenol-D composites

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 (P-s) and volume fraction of Terfenol (V-f) are investigated as functions of applied field and stress bias. At zero stress bias magnetisation (M) is independent of P-s and directly proportional to V-f It is found that magnetostriction (lambda) and differential strain coefficient (d) are both independent of V-f and P-s, 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 lambda versus M indicate that the magnetisation process within the material consists of both domain wall motion and rotation.