Effect of Hoop-Stress on Torque Sensing Using Inverse Magnetostriction of FeGaAlZrC Alloy Ring

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 (lambda), residual magnetization (M-r), applied or residual stresses (sigma) of the ring. Beside, the hoop stress (sigma(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 mu m and hoop stress (sigma(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 mu m and drastically decreased in the case of minimum gap of 6 mu m. 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.