Magnetostrictive properties of nanocellulose Terfenol-D film composite

In this study, we present the results of the preliminary experimental evaluation of the magnetomechanical properties of a novel magnetostrictive composite material. The composite is comprised of particles of Terfenol-D, a giant magnetostrictive alloy, interspersed within a cellulose nanofibril (CNF) reinforced phenol formaldehyde (PF) film matrix. Due to the magnetostrictive properties of Terfenol-D, the composite is able to couple magnetic and mechanical energies in a reversible process. In its monolithic form, Terfenol-D faces several limitations. Namely, it is brittle with a relatively low tensile strength, and experiences significant energy losses at operating frequencies over 1 kHz due to hysteresis and eddy currents induced within the material. When integrated into a composite such as the one presented, both the tensile strength and operating bandwidth of the material are significantly enhanced due to the mechanical and dielectric properties of the matrix. In the case of the CNF composite, there are additional benefits of the natural abundance of the CNF material, and tunable mechanical properties via control of the CNF component of the composite. The work presented encompasses a preliminary analysis of both the magnetostrictive and Villari (inverse magnetostrictive) responses of the composite, as well as some optimization work.First, the actuation behavior of a unimorph structure was explored. The test sample consisted of two discrete layers of nanocellulose, with one active layer containing Terfenol-D. Upon the application of an external magnetic field axial to the sample, an angular deflection of the sample was observed due to magnetostrictive strain in the active layer. As expected, the direction of the deflection was reversed when the sample was reoriented such that the active layer was on the opposite side.Then an attempt to optimize the magnetostrictive response of the composite was made. The magnetostrictive effect is based on the rotation of magnetic domains of a ferromagnetic material from their equilibrium positions to the direction of the applied magnetic field. Therefore, the change in strain can be maximized by biasing these domains initially to a direction orthogonal to the applied field. To achieve this, the composite films were exposed to a DC biasing magnetic field during their fabrication, aligning Terfenol-D particles along the direction of the biasing field