A study is presented to investigate a magnetostrictive flow sensor for use in a scour monitoring system. Using a thin
Galfenol “whisker” a sensor is constructed to detect the presence of water flow. Due to the desire for the whisker to
respond dynamically rather than with just a quasi-static deflection when in a steady stream of flowing water, two
configurations of the sensor are tested, one in which only the bare whisker is exposed to the water flow and one in which
an unstable airfoil is fixed to the whisker. Three primary conclusions are inferred. First, the study confirms that
Galfenol has the structural properties necessary to create a tactile sensor. Second it has been demonstrated that this
tactile sensor is capable of being sensitive to water flow. Finally, it has been determined that alterations to the geometry
of the whisker, specifically the addition of an unstable airfoil, can create the necessary dynamic response required for
such a sensor.
This paper presents the development of a Galfenol-based directional magnetostrictive patch transducer (MPT) and the
results of experimental investigations with the developed MPT for guided Lamb wave (GLW) applications. We used
three magnetostrictive materials such as nickel, polycrystalline Galfenol, and single-crystal-like Galfenol (i.e. a highly
textured Galfenol) with a 1-inch-diameter thin disc form to design the proposed MPT used to evaluate the directionality
for sensing the GLW propagation in thin aluminum plates. Prior to the GLW inspection using the MPTs, the
magnetostriction of the magnetostrictive patches was experimentally measured by a strain gauge, and electron
backscatter diffraction (EBSD) patterns were captured and analyzed to explore grain configurations and crystal
orientations of the patches. The material level analysis validated that the highly textured Galfenol behaves like a single
crystal with large magnetostriction along a <100> orientation. Therefore, the developed MPT using the single-crystallike
Galfenol was expected to exhibit high directional sensitivity of the GLWs traveling in the metallic plate,
corresponding to the preferred orientation of the Galfenol patch. The experimental study of the MPT-based GLW
approach demonstrated that the MPT using the single-crystal-like Galfenol exhibits excellent sensitivity to the incoming
GLWs along the <100> preferred direction, while the nickel-based MPT has omnidirectional GLW sensitivity in the
plate specimen. In addition, the MPT using the polycrystalline Galfenol showed two preferred directions for sensing the
GLWs, corresponding to <110> orientations.
Galfenol is an iron-gallium alloy that exhibits magnetostrictive behavior up to approximately 350
ppm. It has been shown that Galfenol exhibits a linear response in strain that follows commercially
available strain gauges when a magnetic bias field is placed near the Galfenol patch in a bending
test. In this study we extend these results to use of a Galfenol patch for measuring torque. The
benefits of Galfenol-based torque sensors over existing strain sensors for measuring torque are (1)
the potential for use of stray magnetic fields for non-contact torque measurement; (2) ease of
integration and/or retrofit of the proposed torque measuring capability into existing hardware; and
(3) an inexpensive yet mechanically robust alternative to torque sensors that require slip rings or
wireless signal transmission.
This research will show that when placed on a circular shaft at ± 45o relative to the shaft axis,
Galfenol will exhibit a linear response to shear strain produced when a torque is applied to the shaft.
By showing that measurement of shear strain is possible it is evident that the torque on the shaft can
also be determined. A Hall Effect sensor will be rigidly attached to a non-rotating component of the
measurement frame supporting the shaft, and used to determine the change in the magnetic field
above the patch. While the shaft is rotating the response from the Hall Effect sensor is monitored to
determine the torque load on the shaft.
The surface-energy-induced selective grain growth with a specific surface plane can be governed in polycrystalline (Fe81.3Ga18.7) + 0.5at.%B alloys doped with sulfur by controlling the segregation of sulfur through conventional rolling and texture annealing, where boron improves ductility due to suppressing grain boundary fracture during rolling process. The textured sheet, which was annealed at 1200°C for 2h under flowing argon and then quenched in water, exhibits a maximum magnetostriction of about 200 ppm along the rolling direction. During an argon annealing process, a convex profile in magnetostriction as a function of annealing time is formed. As the annealing temperature increases, the observed peak in the convex profiles shifts to less annealing time and also narrows. As-rolled (Fe81.3Ga18.7) + 0.5 at.%B + 0.005 at.%S sheets with large amounts of sub-grain which most likely have been deformed by the rolling process have some {100} and {111} grains parallel to the rolling direction. While texture annealing appears to eliminate the majority of the sub-grains present to below 1% of sub-structured or deformed area in the sheet annealed at 1200°C for 2h. From a texture standpoint the some clustered {100} poles were found and ~25° away from the rolling direction. And the {100} poles are centered right on the rolling direction for the highly textured subset.
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