A MICROSTRUCTURAL INVESTIGATION OF THE NONLINEAR RESPONSE OF ELECTRORHEOLOGICAL SUSPENSIONS .2. OSCILLATORY SHEAR-FLOW

In the preceding paper, Part I, the transition from linear to nonlinea r behavior for electrorheological (ER) suspensions under start-up of s teady shear flow was found to first arise from the slight rearrangemen t of unstable structures. In this paper, we investigate the transition to nonlinear behavior for ER suspensions under oscillatory shear flow , focusing on the role of the rearrangement of unstable structures, an d employing experimental and simulation results. Again, we find that n onlinear deformation first arises from these rearrangements, as oppose d to the gross rearrangement or rupture of particulate chains. The Fou rier transform of the simulated time-dependent shear stress is employe d to quantify the dependence of the critical strain on the deformation frequency and electric field strength. The predicted behavior is cons istent with experimental trends. Methods for verifying the predictions are discussed, as well as possible avenues for exploiting this inform ation in improved operating strategies and improved ER fluids.