Dynamic Magneto-Mechanical Analysis of Isotropic and Anisotropic Magneto-Active Elastomers

BackgroundMagneto-active elastomers (MAEs) are soft composite materials comprising ferromagnetic particles in an elastomer matrix which exhibit a magnetically-induced effective modulus change. The change in modulus has been experimentally studied in many MAE formulations using several techniques; however, this makes comparisons between studies difficult, and there lacks a comprehensive study on the dynamic magneto-mechanical properties of MAEs.ObjectiveIn this article, we seek to understand the effect of mechanical loading direction and magnetic field orientation on the dynamic magneto-mechanical response of isotropic and anisotropic MAEs.MethodsWe develop a new apparatus to perform dynamic mechanical analysis of MAEs at frequencies up to 600Hz subject to magnetic fields of varying strength. We measure the magnetically-induced modulus change in MAEs prepared from a single elastomer-particle combination and specimen geometry, systematically varying the anisotropy direction relative to the magnetic field.ResultsOur results show that isotropic MAEs are up to three times stiffer and anisotropic MAEs up to 65 times stiffer than pure elastomer. Of all configurations studied, the longitudinal modulus of anisotropic MAEs exhibits the largest absolute magnetically-induced change while the transverse modulus exhibits the largest relative change. The magnetically-induced change in loss factor depends on anisotropy and loading condition: isotropic MAEs have no change in loss factor while anisotropic MAEs become less lossy at low strain amplitudes but more lossy at high strain amplitudes.ConclusionsThese results provide new insights into the fundamental mechanisms by which microstructure and magnetic field interact to affect the MAE effective properties.