Aerospace Engineering Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2737

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End date: 2009Subject: search.filters.subject.Galfenol

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    Experimental Investigation of the Mechanical Properties and Auxetic Behavior of Iron-Gallium Alloys
    (2009) Schurter, Holly Marie; Flatau, Alison B; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Iron-gallium alloys (known as Galfenol) are a unique material that have shown great potential for numerous applications. They exhibit a strong magneto-mechanical coupling, otherwise known as magnetostriction, which lends itself very well to transducer applications, from the nano-scale to macro scale. In addition, Galfenol is one of only a few metal alloys known to exhibit large auxetic or negative Poisson's ratio behavior. In order to develop any Galfenol-based applications, it will be necessary to understand its mechanical behavior. The goal of the research presented in this thesis therefore is to measure the elastic properties of Galfenol for a range of compositions in order to create a database, as well as present trends in the elastic properties. This is achieved through tensile testing of single-crystal Galfenol dogbone-shaped specimens and through resonant ultrasound spectroscopy (RUS) of small parallelepiped samples.
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    Development and Validation of a Bidirectionally Coupled Magnetoelastic FEM Model for Current Driven Magnetostrictive Devices
    (2009) Graham, Frank; Flatau, Alison; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A bidirectionally coupled magnetoelastic model (BCMEM) has been extended to include electric currents in its magnetic finite element formulation. This enables the model to capture the magnetoelastic behavior of magnetostrictive materials subjected to elastic stresses and magnetic fields applied not only by permanent magnets but also by current carrying coils used often in transducer applications. This model was implemented by combining finite element solutions of mechanical and magnetic boundary value problems using COMSOL Multiphysics 3.4 (Finite Element Modeling software) with an energy-based non-linear magnetomechanical constitutive model. The BCMEM was used to simulate actuator load lines and four point bending results for Galfenol, which were then compared to experimental data. The model also captured the ΔE effect in Galfenol. The BCMEM can be used to study and optimize the design of future current driven magnetostrictive devices.
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    Characterization of Bending Magnetostriction in Iron-Gallium Alloys for Nanowire Sensor Applications
    (2008-11-21) Downey, Patrick; Flatau, Alison; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This research explores the possibility of using electrochemically deposited nanowires of magnetostrictive iron-gallium (Galfenol) to mimic the sensing capabilities of biological cilia. Sensor design calls for incorporating Galfenol nanowires cantilevered from a membrane and attached to a conventional magnetic field sensor. As the wires deflect in response to acoustic, airflow, or tactile excitation, the resultant bending stresses induce changes in magnetization that due to the scale of the nanowires offer the potential for excellent spatial resolution and frequency bandwidth. In order to determine the suitability for using Galfenol nanowires in this role, the first task was experimentally characterizing magnetostrictive transduction in bending beam structures, as this means of operation has been unattainable in previous materials research due to low tensile strengths in conventional alloys such as Terfenol-D. Results show that there is an appreciable sensing response from cantilevered Galfenol beams and that this phenomenon can be accurately modeled with an energy based formulation. For progressing experiments to the nanowire scale, a nanomanipulation instrument was designed and constructed that interfaces within a scanning electron microscope and allows for real time characterization of individual wires with diameters near 100 nm. The results of mechanical tensile testing and dynamic resonance identification reveal that the Galfenol nanowires behave similarly to the bulk material with the exception of a large increase in ultimate tensile strength. The magnetic domain structure of the nanowires was theoretically predicted and verified with magnetic force microscopy. An experimental methodology was developed to observe the coupling between bending stress and magnetization that is critical for accurate sensing, and the key results indicate that specific structural modifications need to be made to reduce the anisotropy in the nanowires in order to improve the transduction capabilities. A solution to this problem is presented and final experiments are performed.
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    Design and Testing of a Galfenol Tactile Sensor Array
    (2006-12-20) Hale, Kathleen; Flatau, Alison; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The smart material Galfenol, Fe(100-x)Ga(x), where 15<x<28, offers a unique combination of mechanical and magnetostrictive properties that are expected to lead to its use in new sensor and actuator concepts. This thesis seeks to determine if Galfenol can be used to develop a 2-dimensional array of force sensors as part of a 3-D magnetic circuit that, if properly scaled, could mimic the tactile force sensing capabilities needed for use in robotic grippers, prosthetic devices, and robotic surgery. This concept takes advantage of the fact that Galfenol is not brittle and its permeability has high sensitivity to mechanical loads. The hypothesis is that applying stress or force to one or more of the Galfenol rods will produce changes in Galfenol's permeability which will produce changes in the flux density distribution in the magnetic circuit that can be used to determine information about both the load's magnitude and location. The studies performed demonstrated that the decrease in permeability of a loaded rod results in complex changes in magnetic flux. Results from this thesis include recommendations for modifications to better match the rod flux density to the applied load levels and prevent rod top separation.