MEchanics GAthering -MEGA- Seminar: Modeling and identification of constitutive behavior for magnetorheological elastomers

Magnetorheological elastomers (MREs) are ferromagnetic particle impregnated rubbers whose mechanical properties are altered by the application of external magnetic fields. Due to their strong magnetoelastic coupling response, MREs are finding an increasing number of engineering applications, thus necessitating accurate techniques for the determination of their effective properties. This is a difficult task since the overall response of an MRE sample does not only depend on the properties of its constituent materials (and its respective microscopic architecture), but also on its shape: an MRE specimen is subjected to Maxwell stresses that exist both inside the MREs and the surrounding air, leading to shape-dependent non-uniform stress fields inside the specimen.

The goal of this work is a combined experimental and 3D finite element (FEM) modeling approach for computing (and subsequently validating) the energy density for MREs that is not biased by the above-mentioned shape effect. We focus here on isotropic MREs with a fixed volume fraction of particles (8.7%), investigated based on a novel experimental technique. Using a variational framework for finitely strained MREs, we present and subsequently implement into an FEM code three different (but equivalent) variational formulations based on different choices of the independent magnetic variable of the free energy function. Using FEM simulations, necessary to account for the shape effect observed in experiments conducted with a specially designed setup at the LMS at Polytechnique, the data obtained from the purely magnetostrictive test are used to fit the three equivalent free energy functions for the isotropic MRE of interest. The thus obtained constitutive models give accurate predictions when used to simulate different (i.e. not used in the constitutive fitting process) magnetostrictive experiments under axial tension. Time permitting some additional MRE applications will also be presented.

This is joint work with my colleagues Profs. K. Danas, L. Bodelot and Dr. J-P. Voropaieff.