Master of Science, The Ohio State University, 2012, Mechanical Engineering

Magnetostrictive materials are a class of smart materials that have the capability to convert mechanical energy to magnetic energy and vice versa. This transfer of energy makes these materials good candidates for both sensing and actuation applications. A device constructed of one of these materials could perform the same function as current parts that utilize several components which would increase the durability, and lead to smaller components. The potential uses of these materials cover a broad range of applications, including self-sensing actuators due to the fact that smart materials are bidirectionally-coupled. An additional benefit in relation to sensors is that magnetostrictive materials can operate in a non-contact fashion. Measuring the magnetic response to a stress input can be done using different non-contact techniques which would reduce the complexity from current force sensors. Galfenol, an alloy of iron and gallium, is a promising material for both actuation and sensing due to the moderately large strain it exhibits under a magnetic field combined with the material's mechanical robustness. Galfenol has properties similar to steel which allow for machining, extruding, and other load bearing applications. These mechanical properties make Galfenol unique relative to other smart materials, which generally are brittle. This research looks to further the study of Galfenol by documenting the behavior of Fe81.6Ga18.4 under various loading conditions in relation to the development of a force sensor. The characterization of these alloys involves applying a stress to the sample and measuring the corresponding change in magnetization. Both major and minor loop responses were observed over a range of stresses and fields. These were compared for sensitivity and used to determine model parameters. Additional minor loop testing was conducted at high frequencies to determine the material's dynamic behavior as a sensor. The sensitivity was observed to decrease with in (open full item for complete abstract)

Committee: Marcelo Dapino Dr (Advisor); Xiaodong Sun (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2009, Mechanical Engineering

Galfenol is a class of smart material that combines moderate magnetostriction (upto 400 ppm) and excellent mechanical strength. In this work two <100> oriented highly textured polycrystalline Galfenol alloys with different Gallium (Ga) content have been characterized. The two alloys have been studied under tensile and compressive loads. Magnetization versus field measurements are presented for the two alloys at different bias stresses ranging from -63.71 MPa to 63.71 MPa. The magnetization versus applied stress measurements are presented for the two alloys at different bias fields. The stress-dependent magnetic susceptibility change of these alloys has been studied; the susceptibility of the higher concentration Ga alloy is more sensitive to stress in the domain rotation region of the magnetization process and operates over a larger stress range, whereas the low Ga concentration sample is more sensitive in the domain wall motion region. The stress-dependent susceptibility change of these alloys can be used to develop a force sensor or a torque sensor. A force sensor which utilizes the principle of stress-dependent susceptibility is demonstrated. The stress range for a force sensor using the two alloys is determined. The same principle can be used to measure the torque in a non-contact way by bonding rolled Galfenol steel on a shaft.The principle is demonstrated by measuring the change in susceptibility that occurs when a rolled Galfenol patch bonded on a non-magnetic substrate is stressed.

Committee: Marcelo Dapino (Advisor); Stephen Bechtel (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2009, Mechanical Engineering

Magnetostrictive materials have the ability to transfer energy between the magnetic and mechanical domains. They deform in response to magnetic fields and magnetize in response to stresses. Further, their stiffness and permeability depend on both magnetic field and stress. Galfenol, an alloy of iron and gallium, is an emerging magnetostrictive material which is unique for its combination of high magnetomechanical coupling and steel-like structural properties. Unique among smart materials, Galfenol can serve both as a structural element and as an actuator or sensor. This work presents nonlinear characterization and modeling of magnetization and strain of Galfenol, and a 3-D system-level model for Galfenol-based transducers. Magnetomechanical measurements are presented which reveal that Galfenol constitutive behavior is kinematically reversible and thermodynamically irreversible. Magnetic hysteresis resulting from thermodynamic irreversibilities is shown to arise from a common mechanism for both magnetic field and stress application. Linear regions in constant-stress magnetization curves are identified as promising for force sensing applications. It is shown that the slope of these linear regions, or the magnetic susceptibility, is highly sensitive to stress. This observation can be used for force sensing; the 19-22 at. % Ga range is identified as a favorable Galfenol composition for sensing, due to its low anisotropy with moderate magnetostriction and saturation magnetization. A thermodynamic framework is constructed to describe the magnetization and strain. An elementary hysteron, derived from the first and second laws, describes the underlying nonlinearities and hysteresis. Minimization of the energy of a single magnetic domain gives expressions for the hysteron states and accurately describes features of the constitutive behavior, including the stress dependence in the magnetization regions and the stress dependence of the location of the burst magnetization regio (open full item for complete abstract)

Committee: Marcelo Dapino PhD (Advisor); Joseph Heremans PhD (Committee Member); Ahmet Kahraman PhD (Committee Member); Menq Chia-Hsiang PhD (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering