Professor Pedro Ponte Castaneda, University of Pennsylvania

Constitutive Models for Magneto-Active Elastomers at Finite Strains: Dipolar Interactions versus Magnetic Torques
When May 20, 2013
from 02:00 PM to 03:00 PM
Where LR8
Contact Name
Contact Phone 01865 283302
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This presentation is concerned with the application of a finite-strain homogenization framework to develop constitutive models for magneto-active elastomers (MAEs) consisting of initially aligned, rigid magnetic particles distributed randomly in an elastomeric matrix. For this purpose, a novel strategy is proposed to partially decouple the mechanical and magnetostatic effects in the composite. Thus, the effective electro-elastic energy of the composite is written in terms of a purely mechanical component, together with a magnetostatic component evaluated in the deformed configuration of the composite, as estimated by means of the purely mechanical solution of the problem. The theory predicts the existence of certain “extra” stresses—arising in the composite beyond the purely mechanical and magnetic (Maxwell) stresses—which can be directly linked to changes in the effective magnetic permittivity of the composite with the deformation. For the special case of isotropic distributions of magnetically isotropic, spherical particles, the extra stresses are due to changes in the particle two-point distribution function with the deformation, and are of order volume fraction squared, arising from dipole interactions between the particles. On the other hand, for the case of aligned, ellipsoidal particles, the effect can be of order volume fraction, when changes are induced in the orientation of the particles, as a consequence of magnetic torques on individual particles. The theory is capable of handling the strongly nonlinear effects associated with finite strains and magnetic saturation of the particles at sufficiently high deformations and magnetic fields, respectively. It will be shown that particle rotations can be used to produce relatively large field-induced strains and actuation stresses, as well as to control the instantaneous stiffness of the material.