Iron-Gallium alloys demonstrate moderate magnetostriction (~350 ppm) and saturation material induction (~1 T) under low magnetic fields (~400 Oe) as well as high tensile strength (~500 MPa) and limited dependence of magnetomechanical properties on temperatures between -20°C and 80°C, making them promising materials for sensing and actuation 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 110 MPa and unloading, at magnetic fields ranging from 0 to 891 Oe) were performed on single crystal 19% Ga and 24% Ga samples with longitudinal axis in the [100] direction. The effect of % Ga on Young's modulus, saturation magnetization (Msat), ΔE-effect and d*33 are discussed and explained. Furthermore, it was found that the magnetic field (H) through the sample changed with applied stress. A simple magnetic circuit analysis is developed in the latter part of the paper to model this effect. The ramification of both stoichiometry effects and variation in field on the design of Fe-Ga sensors is discussed.
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 Young's 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 Poisson's ratio of -0.75 to produce a large in-plane auxetic behavior.
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 (Delta) E 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 (Delta) E effect are examined. This conference paper is a shortened version of the paper titled Wide band tunable mechanical resonator employing the (Delta) E effect of Terfenol-D that has been submitted for peer reviewed journal publication.
The variability of Young's 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-D's 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 Young's 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-D's 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-D's Elastic Modulus that has been submitted for peer reviewed journal publication.
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.
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