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Development of magnetorheological elastomer (MRE) materials suitable for fused filament fabrication (FFF)-type additive manufacturing processes is performed. Filament materials are thermoplastic polyurethane (TPU) pellets and Fe3O4 magnetic particles. A trickling method is employed to introduce the materials into the filament extruder at a constant rate, after which they are mixed in a hopper and extruded at 160 °C. The trickling rate of Fe3O4 was controlled to produce different volume concentrations [0%–13% (v/v)]. Micrograph analysis on the cross section of the filaments indicates that magnetic particles are uniformly dispersed in the TPU matrix. As the volume concentration of particles in the matrix is increased over 10% (v/v), the size distribution of magnetic particles is slightly increased, indicating formation of aggregation of magnetic particles. Micropores are observed in the filaments, and the number of pores seem to increase with increasing volume concentration of magnetic particles. A commercial off the shelf (COTS) FFF 3-D printer is successfully used to produce cylindrical MRE samples with different magnetic particle volume concentrations. Magnetorheological (MR) properties of the printed MRE samples are characterized by uniaxial compression testing under different applied magnetic field. Material elastic modulus was found to increase with the intensity of magnetic field for a given magnetic particle volume concentration. The relative MR effect varies from −1.3% to 60% within the studied volume concentrations and applied fields. The samples with 5% (v/v) show the highest MR effect when compared with samples with higher magnetic particle volume concentrations. The results of these experiments confirm that the equivalent energy dissipation of the material rises with the increase in the Fe3O4 concentration of MRE. [ABSTRACT FROM AUTHOR]

Galfenol (FexGa100-x), a magnetostrictive alloy (3/2λ 110-400 ppm) of Iron and Gallium exhibits an in-plane auxetic response in the (110) crystallographic direction. Negative Poisson's ratios have been observed in response to application of stress fields, where values of as low as -0.7 have been reported for compositions of greater than roughly 20% Ga [Zhang et al., J. Appl. Phys. 108(2), 023513 (2010)] and in response to application of magnetic fields, where values of as low as -2.5 have been reported to be expected for compositions of less than roughly 20% Ga [G. Raghunath and A. B. Flatau, IEEE Trans. Magn. (in press)]. Several models have been proposed to understand these two distinct phenomena. Galfenol samples with less than 20% Ga also exhibit an unusual response to an increasing magnetic field applied along the (110) direction. The longitudinal strain which increases initially with applied field experiences a dip (until ~10 mT) before increasing again to reach saturation. The transverse strain increases and reaches a maximum value (at the same field of ~10 mT) and then drops from the maximum by 5%-10% as magnetic saturation is approached [G. Raghunath and A. B. Flatau, IEEE Trans. Magn. (in press)].This work deals with discussing the evolution of magnetic domains in a 16 at. % Ga single crystal Galfenol sample when subjected to magnetic fields in the (110) direction in the (100) plane. The magnetic domains on the surface of mechanically polished Galfenol samples were imaged using Magneto-Optic Kerr Effect microscopy. Simultaneously, the strains along the longitudinal and transverse (110) directions were recorded using a bi-directional strain gauge rosette mounted on the unpolished bottom surface of the planar samples. The energy from the applied magnetic field is expected to grow the (110) oriented domains at the expense of domains oriented along all other directions. But since the plane has an easy (100) axis, we expect the domains to orient along the easy direction before saturating along the applied magnetic field direction. A correlation between the images recorded and the strains observed will be used to understand this shift of domains and bump in strain at low fields. [ABSTRACT FROM AUTHOR]

In this paper, we investigate ultrasonic guided wave (GW) sensing performance of a magnetostrictive composite patch sensor (MCPS) in use of a structural health monitoring system for metallic plates. A composite patch of the MCPS consisted of magnetostrictive powders and binding epoxy, where flake- and granular-type Galfenol and spherical nickel particles were considered to examine the effect of particle shape on sensing capability and directional sensitivity. Galfenol flakes with the surface parallel to the (200) crystallographic planes exhibit good field sensitivities in magnetic and magnetostrictive properties when an in-plane field is applied. Shape anisotropy disappears for the conventional spherical shape, accompanying with a large magnetizing field and poor field sensitivity. The 60-kHz GW was successfully captured by the three different MCPSs. Among them, the MCPS with the Galfenol flakes showed the best sensing performance because of their excellent field sensitivities in magnetization and magnetostriction. In addition, the composite patch was configured into a uniaxial comb shape to promote the magnetic shape anisotropy feature of the magnetostrictive patch by itself. Due to the unique configuration of the Galfenol composite patch, the equivalent MCPS presented outstanding directional sensitivity for the GWs propagating along the orientation of the comb fingers. [ABSTRACT FROM AUTHOR]

Rolling and annealing processes are used for examining the surface-energy-induced secondary recrystallization growth with a specific plane and orientation in polycrystalline Fe-Ga based alloys. A near {100}{001} texture is formed in the sheet annealed at 1200 degree Celsius and the maximum magnetostriction of 220 ppm is obtained in the double annealed sheet with close to the targeted {100}{001} texture.