Alfenol patch-, galfenol patch- and galfenol paint-based torque sensor characterization studies

Alfenol (Fe-Al) and Galfenol (Fe-Ga) are iron-based structural magnetostrictive alloys that, for compositions of ∼81% iron, are increasingly being used in sensing, actuating, and energy harvesting devices [Park et al., AIP Advances 6(5), 056221 (2016)]. Recent improvements in the development of magnetostrictive materials using the deformation processing methods of rolling to produce highly textured thin sheet [Park et al., AIP Advances 6(5), 056221 (2016)] and ball milling to produce (001)-oriented micron-size flakes [S. M. Na, J. Galuardi, and A. B. Flatau, IEEE Transactions on Magnetics 53(11), 1–4 (2017)] provide the opportunity to develop a non-contact torque sensor. Torque-induced shear forces at the surface of a shaft lead to a measurable change in the flux passing through the air above the surface of a shaft to which a magnetostrictive layer has been bonded. The current study builds on prior work which demonstrated that torque influenced the magnitude of magnetic flux in the air gaps located between a piece of Galfenol and the rest of a magnetic circuit [Raghunath et al., Proceedings of the ASME, 2013]. The current work overcomes limitations of the prior work. This work demonstrates that using a magnetostrictive layer made of a patch of Alfenol, an alloy that is less expensive, more ductile, and less magnetostrictive than Galfenol, but has almost the same saturation magnetization of ∼1.5T, slightly outperformed the patches made of Galfenol. Additional contributions of the present work include a first look at the application to a shaft of an epoxy-based paint containing micron-sized flakes of (001)-oriented Galfenol, and a comparison of square and ring-shaped patches (aspect ratios of 1 and of ∼4). Data are presented from quasi-static testing and from dynamic tests at rotational rates of up to 1000 rpm.