Previous studies did by some scholars proved applying a magnetic field during the manufacture process
of polymer-bonded Terfenol-D could orient the magnetic easy direction of the particles along the field
direction and form a pseudo-1-3 structure. Compared to the 0-3 composites composed of Terfenol-D
particles dispersed randomly in a polymer matrix, pseudo-1-3 magnetostrictive composites present
much larger magnetostrictive performance. In this paper, magnetostrictive composites based on
Terfenol-D particles in an unsaturated polyester resin matrix were fabricated under different magnetic
fields. Magentostriction was tested and compared to get the detail effects of orientation fields on
magnetostrictive properties of magnetostrictive composites. Scanning electron microscopy was used to
observe their microstructures. Image analysis was applied to describe the microstructures. The
distribution of the angles between the major axis of the particles and the magnetic field direction was
used to evaluate the arrangement of particles in the matrix quantitatively. The results confirm particle
chain-like structures in composites prepared under larger magnetic field, and show that particle
arrangement changes with the strength of the orientation field, which is result in the changes of
magnetostrictive performance.
In the past ten years, there have been several investigations on the effects of particle size on magnetostrictive properties
of polymer-bonded Terfenol-D composites, but they didn't get an agreement. To solve the conflict among them,
Terfenol-D/unsaturated polyester resin composite samples were prepared from Tb0.3Dy0.7Fe2 powder with 20% volume
fraction in six particle-size ranges (30-53, 53-150, 150-300, 300-450, 450-500 and 30-500μm). Then their
magnetostrictive properties were tested. The results indicate the 53-150μm distribution presents the largest static and
dynamic magnetostriction among the five monodispersed distribution samples. But the 30-500μm (polydispersed)
distribution shows even larger response than 53-150μm distribution. It indicates the particle size level plays a doubleedged
sword on magnetostrictive properties of magnetostrictive composites. The existence of the optimal particle size to
prepare polymer-bonded Terfenol-D, whose composition is Tb0.3Dy0.7Fe2, is resulted from the competition between the
positive effects and negative effects of increasing particle size. At small particle size level, the voids and the
demagnetization effect decrease significantly with increasing particle size and leads to the increase of magnetostriction;
while at lager particle size level, the percentage of single-crystal particles and packing density becomes increasingly
smaller with increasing particle size and results in the decrease of magnetostriction. The reason for the other scholars got
different results is analyzed.
Consideration of demagnetization effect, the model used to calculate the magnetostriction of single particle under the
applied field is firstly built up. Then treating the magnetostriction particulate as an eigenstrain, based on Eshelby
equivalent inclusion and Mori-Tanaka method, the approach to calculate average magnetostriction of the composites
under any applied field as well as saturation is studied. Results calculated by the approach indicate that saturation
magnetostriction of magnetostrictive composites increases with increasing of particle aspect, particle volume fraction
and decreasing of Young' modulus of matrix, and the influence of applied field on magnetostriction of the composites
becomes more significant with larger particle volume fraction or particle aspect.
In recent years, influence of volume, size and shape of particulate, stiffness of the polymeric matrix and mechanical
preload on the magetostrictive property of polymer-bonded Terfenol-D composites have been investigated by several
papers, however, few studies on the effects of the blending soft magnetic particles. In this study, polymer-bonded
Terfenol-D composites composed with 20% volume fraction of Terfenol-D particulate and different volume percentage
of carbonyl iron particle (i.e. 0, 10%, 20%, 30% and 40%) are fabricated. The changes of magnetostriction and magnetic
permeability with changing applied field are tested. The experimental results indicate that with increases of fraction of
carbonyl iron particle, the permeability of the composites increases, but the magnetostrictive property declines. The
change of permeability is explained based on two ideal models, while the change of magnetostriction is explained from
the perspective of energy transforming and mechanical property of matrix.
A novel electric current sensor based on FBG and magnetostrictive composites, which is made from epoxy resin and
Terfenol-D particulates, was fabricated. The relationship between the strain of the sensing head and the magnetic field
intensity was obtained. The new sensor exhibited a good linearity and repeatability, which indicates its potential to be a
practical electric current sensor.
In recent years, increasing research efforts have been devoted to the development of new controllable dampers, in the aim of mitigating vibration of mechanical equipment, automobile, civil construction and so on. Most of the new controllable dampers are made with special performance of smart materials, such as MR/ER fluid, piezoelectric ceramic and shape memory alloy. Although has similar smart performance such as rapid response time, low power requirement and large driving force with those smart materials, magnetostrictive material, especially magnetostrictive composite material is only got attention by a few researchers. In this paper, by analysis character of magnetosrtrictive effect, the possible applications of magnetosrtrictive composite material in area of vibration control are discussed; several new dampers, made with magnetosrtrictive composite material, such as smart friction or viscous dampers are presented.
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