Rick A. Kellogg

Temperature and stress dependencies of the magnetic and magnetostrictive properties of Fe0.81Ga0.19

It was recently reported that the addition of nonmagnetic Ga increased the saturation magnetostriction (λ100) of Fe over tenfold while leaving the rhombohedral magnetostriction (λ111) almost unchanged. To determine the relationship between the magnetostriction and the magnetization we measured the temperature and stress dependence of both the magnetostriction and magnetization from −21 °C to +80 °C under compressive stresses ranging from 14.4 MPa to 87.1 MPa. For this study a single crystal rod of Fe0.81Ga0.19 was quenched from 800 °C into water to insure a nearly random distribution of Ga atoms. Constant temperature tests showed that compressive stresses greater than 14.4 MPa were needed to achieve the maximum magnetostriction. For the case of a 45.3 MPa compressive stress and applied field of 800 Oe, the maximum magnetostriction at 80 °C decreases from its value at −21 °C by 12.9%. This small magnetostrictive decrease is consistent with a correspondingly small 3.6% decrease in magnetization over the sam...

Experimental Investigation of Terfenol-D's Elastic Modulus

The variability of Youngs modulus (the ▵E effect) in giant magnetostrictive Terfenol-D has a significant impact on the performance and modeling of Terfenol-D transducers. In this investigation, Terfenol-Ds modulus of elasticity is characterized under controlled thermal, magnetic, and mechanical loading conditions. Quasistatic cyclic compressive stress testing methods are used to quantify the variability in Youngs modulus over a wide range of DC applied magnetic fields and stresses. Apparent elastic modulus changes of four-fold or more are demonstrated through the variation of a DC applied magnetic field. The effect of decreasing cyclic stress amplitude giving rise to an increase in Terfenol-Ds apparent elastic modulus is also examined.

Demonstration of polarization-independent resonant subwavelength grating filter arrays

We demonstrate a two-dimensional (2D) polarization-independent resonant subwavelength grating (RSG) in a filter array. RSGs, also called guided mode resonant filters, are traditionally one-dimensional gratings; however, this leads to TE and TM resonances at different wavelengths and with different spectral shape. A 2D grating can remove the polarization dependence at normal incidence, while maintaining the desirable RSG properties of high reflectivity, narrow passband, and low sidebands without ripple. We designed and fabricated 2D gratings with near-identical responses for both polarizations at normal incidence in the telecommunication band. Ninety percent reflectivity is achieved at the resonant wavelengths.

Texture and grain morphology dependencies of saturation magnetostriction in rolled polycrystalline Fe83Ga17

Textured polycrystalline Fe-Ga alloys exhibit magnetostrictive strains of 100 ppm or greater and may function as a mechanically robust actuator/sensing material. Current efforts seek to combine the 300+ ppm magnetostrictive strain performance of [100] oriented single crystals with the mechanical properties of polycrystalline forms. One approach to combining these properties is to control the crystallographic texture through deformation processing such as rolling. To determine the relationship between saturation magnetostriction, degree of texturing, and grain morphology we compare the results of three-dimensional finite element simulations with the analytical solution for a random polycrystal and the experimental responses of rolled polycrystalline Fe83Ga17. Textured specimens were produced through rolling reductions up to 99% of an as-cast ingot and a subsequent 1100 or 590 °C anneal. The high temperature anneal produced a recrystallized grain structure having a wide variation in crystal orientation as d...

Sensing Behavior of Varied Stoichiometry Single Crystal Fe-Ga

Iron-Gallium (Fe-Ga) alloys are promising materials for sensing applications. However, the mechanical and magnetic properties of these materials vary significantly with the percentage of gallium, which motivates this study on the effect of stoichiometry on the behavior of Fe-Ga alloys. Major loop compressive tests (loading to 110MPa and unloading, at magnetic fields ranging from 0 to 891 Oe) were performed on single crystal 19 and 24% Ga samples with longitudinal axis in the [100] direction. The effect of% Ga on the magnetomechanical properties is discussed. Furthermore, the magnetic interaction between the Fe-Ga sample and the remainder of the magnetic circuit is modeled.

Blocked force investigation of a Terfenol-D transducer

The output force-strain relationship typical of the performance of Terfenol-D transducers under varied operating conditions is examined to study transducer blocked force characteristics. The design and construction of a transducer for testing under controlled thermal, magnetic and mechanical load conditions are described. Results of compression tests at various applied magnetic fields and two initial mechanical stress states are used to generate load lines and the blocked force characteristics of the transducer. Comparisons of the transducers force and strain output are made with published data. This test data is also used to examine the variability in Youngs Modulus with applied magnetic field, strain and stress.

Blocked-Force Characteristics of Terfenol-D Transducers

The output force–strain relationship typical of the performance of Terfenol-D transducers under varied operating conditions is examined to study transducer blocked-force characteristics. The design and construction of a transducer for testing under controlled thermal, magnetic and mechanical load conditions are described. Results of compression tests at various applied magnetic fields and two initial mechanical stress states are used to generate load-lines and the blocked-force characteristics of the transducer. Comparisons of the transducer’s force and strain output are made with published data. This test data is also used to examine the variability in Young’s modulus with applied magnetic field, strain and stress.

Wide Band Tunable Mechanical Resonator Employing the ΔE Effect of Terfenol-D

The control of Terfenol-D’s operational elastic modulus offers opportunities for novel devices and applications capitalizing on real-time changes in material stiffness. This work describes the development and testing of a Terfenol-D transducer employed as a wide-band variable frequency mechanical resonator. The design and construction of such a wide-band mechanical resonator for testing under controlled thermal, magnetic and dynamic mechanical load conditions are described. Changes in Terfenol-D’s elastic modulus, the ΔE effect, approaching 266% are demonstrated in the mechanical resonator utilizing a range of d.c. applied magnetic field levels of less than 61.0 kA/m. The elastic modulus and damping characteristics of Terfenol-D, critical to the successful design of devices employing the ΔE effect, are examined.

Mechanical properties of magnetostrictive iron-gallium alloys

Single crystal specimens of Fe-17 at. % Ga were tested in tension at room temperature. Specimens with a tensile axis orientation of [110] displayed slip lines on the specimen faces corresponding to slip on the {110}<111> with a critical resolved shear stress of 220 MPa. Yielding began at 0.3% elongation and 450 MPa. An ultimate tensile strength of 580 MPa was observed with no fracture occurring through 1.6% elongation. The Young’s modulus was 160 GPa in the loading direction with a Poisson’s ratio of -0.37 on the (100) major face. A specimen with a tensile axis orientation of [100] showed slip lines corresponding to slip on the {211}<111> with critical resolved shear stress of 240 MPa. Discontinuous yielding began at 0.8% elongation, which was thought to result from twinning, kink band formation, or stress-induced transformation. The Youngs modulus was 65 GPa in the loading direction with a Poisson’s ratio of 0.45 on the (001) major face. A maximum tensile strength of 515 MPa was observed with fracture occurring after 2% elongation. A sizeable elastic anisotropy of 19.9 was identified for Fe-27.2 at. % Ga accompanied by a Poissons ratio of -0.75 to produce a large in-plane auxetic behavior.

Stress-strain relationship in Terfenol-D

The variability of Youngs modulus (the (Delta) E effect) in giant magnetostrictive Terfenol-D has a significant impact on the performance and modeling of Terfenol-D transducers. While elastic modulus variability introduces nonlinearities in the transducer input/output relationship that are often deemed undesirable, it also affords opportunities for achieving novel device performance attributes. In this investigation, Terfenol-Ds modulus of elasticity is characterized under controlled thermal, magnetic, and mechanical loading conditions. Quasi-static cyclic compressive stress testing methods are used to quantify the variability in Youngs modulus over a wide range of d.c. applied magnetic fields and stresses. Elastic modulus changes of four-fold or more are demonstrated through the variation of a d.c. applied magnetic field. The effect of decreasing cyclic stress amplitude giving rise to an increase in Terfenol-Ds apparent elastic modulus is also examined. The thermally controlled transducer used throughout this investigation is described. This conference paper is a shortened version of the paper titled Experimental Investigation of Terfenol-Ds Elastic Modulus that has been submitted for peer reviewed journal publication.