ON CONSTITUTIVE-EQUATIONS FOR ELECTRORHEOLOGICAL MATERIALS

Constitutive equations for electrorheological (ER) fluids have been ba sed on experimental results for steady shearing flows and constant ele ctric fields. The fluids have been modeled as being rigid until a yiel d stress is reached. Additional stress is then proportional to the she ar rate. Recent experimental results indicate that ER materials have a regime of solid-like response when deformed from a rest state. They b ehave in a viscoelastic-like manner under sinusoidal shearing and exhi bit time-dependent response under sudden changes in shear rate or elec tric field. In this work, a constitutive theory for ER materials is pr esented which accounts for these recent experimental observations. The stress is given by a functional of the deformation gradient history a nd the electric field vector. Using the methods of continuum mechanics , a general three-dimensional constitutive equation is obtained. A sam ple constitutive equation is introduced which is then used to determin e the response of an ER material for different shear histories. The ca lculated shear response is shown to be qualitatively similar to that o bserved experimentally.