Magnetorheology in viscoplastic media

Suspensions of iron particles in media with yield stresses were investigate d to determine the effect of the continuous phase yield stress on the magne torheological (MR) response. The steady-shear MR response was independent o f the continuous phase yield stress for yield stresses in the range 0.9-37 Pa. The field-induced suspension yield stress increased sub-quadratically w ith the flux density. The small amplitude oscillatory sheer response exhibi ted history dependence. The storage modulus depended not only on the magnit ude of the applied magnetic field. but also on its history. This history de pendence can be explained in terms of the field-dependent evolution of the suspension microstructure.