Nersesse Nersessian

Dynamic magnetomechanical behavior of terfenol-D/epoxy 1-3 particulate composites

We investigated the dynamic behavior of 1-3 type magnetostrictive particulate composites as a function of both bias field (5-140 kA/m) and frequency (1-100 kHz). The composites consist of approximately 0.5 volume-fraction Terfenol-D particles embedded and magnetically aligned in a passive epoxy matrix. The measured properties include elastic moduli (E/sub 3//sup H/ and E/sub 3//sup B/), dynamic relative permeability (/spl mu//sub r33/), dynamic strain coefficient (d/sub 33/), magnetomechanical coupling coefficient (k/sub 33/), and the ratio of the dynamic strain coefficient to the dynamic susceptibility (d/sub 33///spl chi//sub 33/). We observed the dependence of these properties on bias field and explain it here in terms of domain-wall motion followed by saturation near 40 kA/m. The spectra of /spl mu//sub r33/, d/sub 33/, and d/sub 33///spl chi//sub 33/ indicate that the magnetization process is independent of frequency and that the effect of eddy-current losses is insignificant up to 100 kHz. The observations agree with predictions made by classical eddy-current theory and suggest that the composites can be operated at significantly higher frequencies than monolithic Terfenol-D.

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

Abstract This paper describes magneto-thermo-mechanical test results for 1–3 type magnetostrictive composites incorporating Terfenol-D (Tb 0.3 Dy 0.7 Fe 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 ( e 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.

Magnetoelectric behavior of Terfenol-D composite and lead zirconate titanate ceramic laminates

Five magnetoelectric laminates of polymer-bonded Terfenol-D magnetostrictive composite (i.e., volume fractions (V/sub p/) ranging from 0.16 to 0.48) and lead zirconate titanate (PZT-5H) piezoelectric ceramic were fabricated. The measured quasistatic magnetoelectric voltage coefficient (/spl alpha//sub E/) increased gradually with increasing V/sub p/ and approached saturation for V/sub p/>0.4 due to increased elastic modulus and piezomagnetic coefficient of the magnetostrictive phase. A maximum /spl alpha//sub E/ of 2.7 V/cm/spl middot/Oe was observed at a magnetic bias field (H/sub Bias/) of 53 kA/m for the laminate with V/sub p/=0.48. /spl alpha//sub E/ was found to be a fairly linear function of H/sub Bias/ at 100-220 kA/m bias for all V/sub p/ values. d/spl alpha//sub E//dH/sub Bias/ as a function of H/sub Bias/ was found to increase with increasing V/sub p/ for H/sub Bias/ values of 100-220 kA/m.

Dynamic magnetomechanical properties of [112]-oriented Terfenol-D/epoxy 1–3 magnetostrictive particulate composites

The dynamic magnetomechanical properties of a Terfenol-D/epoxy 1–3 magnetostrictive particulate composite fabricated using 49% volume fraction of needle-shaped, [112]-oriented Terfenol-D particles were investigated as a function of magnetic bias field (HBias). A nonoriented composite with 51% volume fraction of irregular-shaped, ball-milled Terfenol-D particles was also prepared and characterized for comparison. It was found that the composites exhibit a similar qualitative trend in dynamic strain coefficient (d33) and dynamic susceptibility (χ33) with the oriented type possessing much higher values than the nonoriented type for all HBias. Data for the ratio d33/χ33 indicated that these increments in d33 and χ33 in the oriented composite are mainly attributed to [112] particulate crystallographic orientation.

Gd5Si2Ge2 composite for magnetostrictive actuator applications

A composite system containing particles of Gd5Si2Ge2, which exhibit a colossal magnetic-field-induced strain, has been prepared. The composite is manufactured by embedding ball-milled Gd5Si2Ge2 particles with a size distribution of <600 μm in a resin matrix. The thermally induced volume strain in the composite resulting from phase transformation is found to be 1300 ppm. The magnetically induced linear strain resulting from phase transformation is also measured, from which the volume strain is deduced to be 1650 ppm. The volume strain from the composite is significantly lower than phase transformation strain of the bulk Gd5Si2Ge2 (8000 ppm) and is mainly attributed to nonalignment of the particles in the matrix. An analytical model for a 1–3 composite (particles aligned in a single direction in a polymer matrix) and a 0–3 composite (particles dispersed randomly in a polymer matrix) predicts significantly higher strains in a 1–3 composite.

Hollow and solid spherical magnetostrictive particulate composites

Nickel microspheres were produced by the spark erosion technique under both liquid nitrogen and water conditions. Density measurements and Scanning electron microscope analysis revealed that a significant portion of the Ni particles produced under the liquid nitrogen conditions are hollow spheres with a density of 6.67(4)g∕cm3 while the particles produced in water are primarily solid spheres with a density of 8.40(1)g∕cm3, close to the bulk nickel value of 8.90g∕cm3. Nickel∕polymer composites incorporating the hollow and solid nickel microspheres were manufactured with volume fractions of 25% and 36%, respectively. The hollow and solid nickel composites exhibited saturation magnetostrictions of −24 and −28ppm, respectively. In addition, small quantities of Terfenol-D (Tb0.3Dy0.7Fe2) were spark eroded under liquid argon conditions with ∼10% by volume of the spark eroded particles being solid microspheres. Calculations indicate that aligned composites that incorporate these Terfenol-D microspheres could rea...

Dynamic magnetomechanical behavior of Terfenol-D/epoxy 1-3 composite

This paper presents an experimental investigation of the dynamic behavior of a 1-3 type magnetostrictive composite, with emphasis on the evaluation of fundamental material properties pertinent to device design. The fabricated 1-3 magnetostrictive composite comprises 51 percent volume fraction of Terfenol-D particulates embedded and magnetically aligned in a passive epoxy matrix. The dynamic magnetomechanical properties of the composite are measured as functions of bias field, drive field, and frequency. These properties include Youngs moduli at constant magnetic field strength (EH3) and at constant magnetic flux density (EB3), magnetomechanical coupling coefficient (k33), dynamic relative permeability (ur33), dynamic strain coefficient (d33), mechanical quality factor (Qm), and the ratio of the dynamic strain coefficient to the dynamic susceptibility. Dependence of material properties on applied fields and frequency is observed with no evidence of eddy current losses. The observed eddy current effect agrees with the prediction of classical eddy current theory. This suggests that the composite can provide superior high-frequency performance as compared to monolithic Terfenol-D and laminated Terfenol-D systems. Implications for high-frequency applications of the material to resonance devices are also described.

Magneto-thermo-mechanical characterization of magnetostrictive composites

This paper describes magneto-thermo-mechanical characterization of magnetostrictive composites. 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 actuator and sensor systems that incorporate these materials. Currently the composites are being used in sonar transducers. The magnetostrictive composite contains Terfenol-D (Tb0.3Dy0.7Fe2) particulate embedded into an epoxy binder. Composite form is used due to the relative brittleness and limited operational frequencies of monolithic Terfenol-D. Two different tests were performed both at room temperature and under thermal loading: 1) constant magnetic field with cyclically varying load around a bias load and 2) constant pre-load with varying magnetic field. Testing was performed on five different volume fraction composites, namely, 10%, 20%, 30%, 40% and 50%. Parameters that were evaluated include strain output, magnetic field, magnetization and elastic modulus. Results for the constant magnetic field tests indicate that modulus generally increases with increasing volume fraction and increasing magnetic field. However, for low fields, an initial dip is noticed in modulus (i.e. (Delta) E effect) attributed to domains becoming more mobile at lower magnetic field levels. Results also indicate an increase in modulus with decrease in temperature. Results for the constant load test indicate a strong dependence of strain output on applied pre-stress. Results indicate that max strain peaks at a certain value of the pre-stress and then decreases for increasing pre-stress. Results also indicate that strain output peaks between 0 degree(s)C and +10 degree(s)C and that strain generally increases with increasing volume fraction.

Temperature- and magnetic-field-induced phase transormation in bulk and cmoposite Gd5Si2Ge2

A -1300ppm strain has been obtained in a [0-3], resin binder, Gd5Si2Ge2 particulate composite. The strain is a result of a temperature induced phase transformation from a high volume (high temperature, low magnetic field) monoclinic phase to a low volume (low temperature, high magnetic field) orthorhombic phase. The particles used in the composite were ball-milled from a bulk sample and were sieved to obtain a size distribution of <600micron. Bulk Gd5Si2Ge2 was manufactured via arc melting and subsequently annealed at 1300°C for 1 hour to produce a textured, polycrystalline sample. The transformation temperatures of the bulk sample, as measured using a Differential Scanning Calorimeter (DSC), were Ms=-9.3°C, Mf=-14.6°C, As=-4.4°C, and Af=-1.2°C. The bulk sample was magnetically characterized using a SQUID magnetometer, and found to undergo a paramagnetic to ferromagnetic transition during the phase transformation, consistent with published results. The bulk sample was also found to possess a -8000ppm volume magnetostriction, agreeing well with measured unit cell parameters of the different phases.

Magnetoelectric Effect in Magnetostrictive/Polymer and Piezoelectric Composites

A 1200m V/cmOe magnetoelectric voltage coefficient was measured in a Terfenol-D/epoxy and PZT-5H[2-2] composite. The magnetoelectric effect is a result of a coupling between the magnetostrictive (Terfenol-D/epoxy) and piezoelectric (PZT-5H) layers. The coupling was achieved mechanically by bonding the piezoelectric layer in between two magnetostrictive layers. The maximum in magnetoelectric voltage coefficient was measured at a frequency of 8Hz and a bias magnetic field of 103kA/m. The magnetoelectric voltage coefficient was observed to be highly dependent upon the bias magnetic field.Copyright