Characteristics of a Magnetostrictive Composite Stress Sensor

A magnetostrictive composite material (MCM) of a giant magnetostrictive alloy, Terfenol-D (Tb0.3Dy0.7Fe2), and epoxy resin has been used to fabricate mechanical stress sensors that are electrically isolated and based on the Villari effect (or inverse magnetostriction). Under an external mechanical stress, magnetic domains in the MCM rotate and expand proportionally, modifying the magnetic properties due to the Villari effect. We designed a probe consisting of a toroidal, laminated, air-gapped silicon steel core with a tightly wound coil that facilitated monitoring the change in the magnetic susceptibility of the MCM. Since the coil is wound around the core and the air gap is partially filled with the MCM, the change in magnetic susceptibility of the MCM can be estimated by performing inductance measurements. We investigated the effect of the angle between the stress and magnetic susceptibility measurement axes on the response of MCM sensors mounted at different angles onto 6061-T6 aluminum substrates. This sensing technique can be used for non-destructive evaluation and monitoring the integrity of various mechanical and civil engineering structures. This wireless technique might also be extendable to measure the stress vector.