APPLICATION OF A NONLINEAR PHENOMENOLOGICAL MODEL TO THE OSCILLATORY BEHAVIOR OF ER MATERIALS

Electrorheological fluids can exhibit highly nonlinear behavior for la rge electric-field strengths and strains. Oscillatory rheometry of the se activated suspensions can, in some cases, result in the dynamics of the rheometer contributing to the measured shear stress within the ER material. Some experimental results are presented for an activated el ectrorheological fluid for a range of experimental conditions. These r esults show how the material behaves under an increasing electric fiel d, for certain levels of strain and oscillatory frequencies. The resul ts also show the effects of the inertia of the viscometer on the obser ved characteristic behavior of the material, and a method of removing this component from the data is discussed. A three element mechanical analogy of the ER material is presented, which together with the intro duction of an inertial term models well the behavior seen in the exper imental results. By taking into account some of the influences of the experimental apparatus, the proposed model is used to put forward some hypotheses for the characteristic physical response of an activated E R material. (C) 1995 Society of Rheology.