Fig. 1 Elements of the torque transducer and the magnetic parameters concerning with ring type torque sensor by using inverse magnetostriction. (H T =Magnetization strength, M r =Residual magnetization, s=Applied stress) Galfenol (FeGaAlZrC) alloy ring was used for torque sensing by detecting a leakage flux from the ring surface based on the inverse magnetostriction effect. This leakage flux changes depending on the magnetic parameter such as magnetostrictive strain (l), residual magnetization (M r ), applied or residual stresses(s) of the ring. Beside, the hoop stress (s h )which is one of the residual stress factor in the ring also has strong effect on torque sensing because this affects those magnetic parameters. The fitting gap between ring and shaft was four kinds of 6, 10, 20 and 30 mm and hoop stress (s h ) in each case can be estimated from the elastic formula of material mechanics. As a result, torque sensitivity showed the maximum value in the case of 10 micrometers gap and it decreased toward the gaps of 10 and 20 mm and drastically decreased in the case of minimum gap of 6 mm. This change of torque sensitivity depending fitting gap is discussed based on the magnetic domain mobility and inelastic material effect at the interface of Galfenol ring and rotating shaft.
Ferromagnetic Co Ni alloys of less than 35 atNi exhibit a phase transformation from g phase (FCC) to e phase (HCP): both phases are stable at higher and lower temperatures, respectively. Since both phases of these alloys exhibit high magnetization and thermoelastic martensitic transformation, it is expected as new ferromagnetic shape memory alloy. In this study, We prepared a rapid solidified Co 32 atNi foil and analyzed thermoelastic and stress induced martensite phase in temperature range of 77 to 673 K from observation of the texture, structure, magnetic property and Barkhausen noise. From these results, it is found that 1) the thermoelastic martensitic transformation is not reversible and 2) a stress induced martensite phase is transformed to a austenite phase by heating. The result is caused by the mechanism of the transformation from a g phase (HCP) to a e phase (FCC).
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