Terfenol-D Composites Research Articles

Magneto-thermo-mechanical characterization of 1–3 type polymer-bonded Terfenol-D composites

This paper describes magneto-thermo-mechanical test results for 1–3 type magnetostrictive composites incorporating Terfenol-D (Tb 0.3Dy 0.7Fe 2) particulate in an epoxy binder. The purpose of this study is to evaluate the behavior of magnetostrictive composites under combined magnetic, thermal, and mechanical loading, and to determine fundamental properties used for design of sonar transducers that incorporate these materials. Two different tests were performed both at room temperature and under thermal loading: (1) constant magnetic field with cyclically varying mechanical load around a bias load, and (2) constant mechanical pre-load with cyclically varying magnetic field. Testing was performed on five different volume fraction ( V p ) composites, namely, 13%, 23%, 31%, 37%, and 50%. Parameters that were evaluated include strain output ( ε 3) and elastic modulus ( E 3 H ). Detailed analysis, including relative permeability ( μ 33 σ / μ 0) and the piezo-magnetic coefficient ( d 33), is only presented for the composite with 50% V p . Results indicate that composite properties, as pertaining to sonar transducers, are comparable to monolithic Terfenol-D while reducing brittleness, providing higher operational frequencies and easier manufacturability. Moreover, results for composite Terfenol-D can be explained well using theory developed for monolithic Terfenol-D.

112] Oriented Terfenol-D Composites

This paper describes the manufacture and testing of polymer matrix Terfenol-D particulate composites fabricated with a [112] preferred crystal orientation. The results demonstrate that crystal orientation permits higher saturation strain than previously obtained in particulate composites. Oriented particle composites were fabricated using needle shaped Terfenol-D particulate made from commercially available [112] textured polycrystals. A magnetic field applied during manufacture oriented the particles along their longest dimension. Three materials of 22, 36, and 49% particulate volume fraction, were produced and tested to obtain the magnetostriction at constant mechanical loads from 0.5 to 16 MPa. Results demonstrate that crystallographically oriented particle composites saturate at 1475 microstrain whereas the previous non-oriented particle composite saturates at 1150 microstrain. The authors attribute the increased magnetostriction to a predominance of particle orientation along the [112] crystal direction. Modulus measurements indicate that the composites can be described using an upper bound 1–3 composite model. Upper bound rule of mixtures models show that the 36% and 49% oriented particle composites exhibit 94% and 90% respectively of the predicted upper bound magnetostriction. Further rule of mixtures models are used to illustrate how applied stress increases the effective anisotropy in composites as a function of particulate volume fraction. The results demonstrate that by preferential orientation of particles, Terfenol-D particulate composite materials may be fabricated with magnetostriction properties close to that of bulk Terfenol-D.

Effective magnetostriction and magnetomechanical coupling of terfenol-D composites

Epoxy and glass matrix Terfenol-D composites have been produced by using a cold and hot compression-molding technique, respectively. The static and dynamic magnetic and magnetomechanical properties of samples with a volume fraction Vf in the range of 10% to 82% have been investigated as functions of bias field, frequency, and ac drive field. The epoxy composites have a greater saturation magnetostrain than the glass composite with the same Vf. The elastic modulus of the epoxy composites is dominated by that of the matrix, Em. Increasing the value of Em reduces the measured magnetostriction λc of the composites. A model, based on the strain related energy equilibrium, has been developed to describe the experimental results for Vf and Em dependences of λc and the magnetomechanical coupling coefficient k33. It is concluded that an optimum k33 value can be obtained by choosing a matrix with an appropriate elastic modulus.

Dynamic magneto-mechanical properties of epoxy-bonded Terfenol-D composites

The dependence of the dynamic magneto-mechanical properties of epoxy-bonded Terfenol on the composition parameters of particle size ( P s) and volume fraction of Terfenol ( V f) is investigated as functions of bias field ( H) and high frequency ( f). Samples were prepared with powder in five size ranges between 106 and 710 μm using three volume fractions. The dynamic strain coefficient ( d) and magneto-mechanical coupling coefficient ( k) were found to be independent of P s and V f while the dynamic relative permeability ( μ r) was proportional to V f. d showed less variation with H up to 100 kA m −1, than for bulk Terfenol with d also exhibiting a flat response with frequency, up to 20 kHz. The frequency dependence of μ r, up to 200 kHz, was also flat apart from the occurrence, at ∼15 kHz, of a fundamental shape resonance which was also experienced by d. Classical eddy current theory was used to model the behaviour of μ r with f and it was found that experiment and theory were qualitatively similar.

Effect of the elastic modulus of the matrix on the coupling of magnetostrictive composites

The magnetomechanical coupling coefficient, k/sub 33/, has been modeled as a function of the elastic modulus of the matrix, E/sub m/, of composite magnetostrictive materials. Measurements of k/sub 33/ have been performed by a three-parameter technique on glass-matrix Terfenol-D composites fabricated from powders heated to 700/spl deg/C in an inert atmosphere under the application of a 1-3 kN force. It is concluded that there is a value of E/sub m/ for optimum magnetomechanical performance which is dependent on the volume fraction, V/sub f/. The optimum value of E/sub m/ is close to, but less than, the elastic modulus of the magnetostrictive material.

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 (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 rotation.

Magnetostrictive properties of polymer-bonded Terfenol-D composites

Polymer-bonded Terfenol-D composites are fabricated using powders with varying sizes and also under various production conditions, in an effort to produce Terfenol-D bulks with good magnetostrictive properties through the optimization of the many fabrication parameters. A large magnetostriction of 536 ppm at 1.1 kOe, combined with a high d max 33 (the maximum slope in the magnetostriction–applied magnetic field curve) of 1.3 ppm/Oe (16.3 nm/A) is obtained for the composite fabricated at the following conditions; the average particle size of 137.5 μm, a phenol content of 3.1 wt%, and a compaction pressure of 0.5 GPa. The magnetostrictive properties achieved in this work are much better than the previously reported results for similar Terfenol-D composites.

Analysis and optimization of the magnetomechanical properties of Terfenol-D composites at audio frequencies

The magnetic and magnetostrictive properties of polymer-bonded Terfenol-D rods, compacted from powders with different phenol binder content, are measured in static and dynamic conditions. Magnetic measurements were made up to 40 kHz using a custom made amorphous yoke. Magnetostrictive characterization was performed with prestress up to 15 Mpa in quasi-static and dynamic conditions (up to 40 Hz). A maximum deformation of about 6/spl times/10/sup -4/, producing work, can be achieved with a variable phenol content. Dynamic magnetic properties were simulated using the dynamic Preisach model, obtaining an estimate value for conductivity. The inclusion of a non-conductive phenol binder increases the mechanical strength and favors a reduction of eddy current losses, for applications at sonic or ultrasonic frequency.

Energy Absorption and Damping in Magnetostrictive Composites

AbstractThe mechanical energy absorption characteristics of several polymer matrix Terfenol-D composites were evaluated experimentally. Magnetostrictive composites absorb energy through domain level processes that couple mechanical and magnetic energies. The testing consisted of mechanically cycling the materials at different stress amplitudes (combined compression and tension) at a single frequency. Results indicate that the magnetostrictive composites exhibit a unique combination of high damping properties in conjunction with a relatively high modulus. The measured tan delta values for the materials are functionally dependent upon the stress amplitude. In general, as the stress amplitude increased, the damping or energy absorbed during one cycle decreased. Results also indicate that damping is directionally dependent (i.e. anisotropic) and that bias magnetic fields decrease the energy absorption. The volume fraction of the composites did not play a significant role in the magnitude of damping. This effect may be related to the inherent pre-stress imparted on the particle by the resin during cure.