Quasi-static major and minor strain-stress loops in textured polycrystalline Fe81.6Ga18.4 Galfenol

The ΔE effect (Young's modulus variation of magnetostrictive materials) is useful for tunable vibration absorption and stiffness control. The ΔE effect of iron-gallium (Galfenol) has not been fully characterized. In this study, major and minor strain-stress loops were measured under different bias magnetic fields in solid, research grade, ⟨100⟩-oriented, highly-textured polycrystalline Fe81.6Ga18.4 Galfenol. A 1 Hz, constant amplitude compressive stress was applied from −0.5 MPa to −63.3 MPa for major loop responses. Minor loops were generated by simultaneously applying a 4 Hz, 2.88 MPa amplitude sinusoidal stress and different bias stresses ranging from −5.7 MPa to −41.6 MPa in increments of about 7.2 MPa. Bias magnetic fields were applied in two ways, a constant field in the sample obtained using a proportional-integral (PI) controller and a constant current in the excitation coils. The ΔE effect was quantified from major and minor loop measurements. The maximum ΔE effect is 54.84% and 39.01% for constant field and constant current major loops, respectively. For constant field and constant current minor loops, the maximum ΔE effect is 37.90% and 27.46%, respectively. A laminated sample of the same material was tested under constant current conditions. The saturation modulus of this material is 59.54 GPa, or 82.65% of the solid rod's saturation modulus, due in part to the soft adhesive layers. The minimum modulus calculated from major loops is 36.31 GPa, which corresponds to a 39.02% ΔE effect. A new optimization procedure is presented on the basis of an existing discrete energy-averaged model to incorporate measurement uncertainties. The model was optimized to both major and minor loop data; model parameters with 95% confidence intervals are presented.