Magnetostrictive bending of cantilever beams and plates

Abstract

The models currently used to determine strains, stresses, and deflections in beams and plates made of magnetostrictive films deposited on nonmagnetic substrates are based on the assumption that the film is relatively thin compared to the substrate. Despite the lack of self-consistency and the limitations of these models, they can be used to calculate approximate strains and deflections when the ratio of the thickness of the film to the thickness of the substrate is smaller than about 0.001; even then they do not consistently predict stresses or energies. Unfortunately, the large deflections required in modern applications are only achievable with films that do not satisfy this assumption of relative film thinness, and the results obtained with the traditional models show large errors. In these circumstances it is necessary to introduce robust methods that can be applied regardless of the relative magnitude of the thickness of the film. In this article, one such method is presented. The method represents a self-consistent approach based on the minimization of the total internal energy of a film-substrate system, performed based on the assumption that the magnetostrictive strains can be modeled as anisotropic expansional strains. The expressions obtained using this approach can be used to calculate strains, stresses, deflections, and energies in an accurate way. The method is suitable for generalization to the cases in which the deformation of beams and plates is produced not only due to magnetostriction in the films, but may also include thermal, piezoelectric, or hygroscopic strains.