Shear flow behavior of confined magnetorheological fluids at low magnetic field strengths

Magnetorheological (MR) fluids are field-responsive suspensions of magnetizable particles which rheological properties can be dramatically altered by applying external magnetic fields (Phulé and Ginder 1998). Under the presence of a magnetic field, anisotropic chainlike structures result from field-induced particle magnetization as a consequence of the permeability mismatch between particle and solvent. The flow behavior of MR fluids is typically described as that of a classical Bingham plastic. Central to the Bingham model is the yield stress, which is a measure of the strength of the material. For applied stresses greater than this value, the material is able to flow, usually, as a Newtonian liquid (Rankin et al. 1998). Many investigations have been done in relation to the non-linear properties (yield and flow behavior) of field-responsive fluids. Marshall et al. (1989) studied the electrorheological response of hydrated poly(methacrylate) particles in a chlorinated hydrocarbon as a function of electric field strength, shear rate, volume fraction, and temperature. The response was analyzed considering the fundamental forces acting on the particles. As a result, it was found that at a given volume fraction, all of the dependencies of the relative viscosity on shear rate, field strength and temperature can be collapsed into a single function of the Mason number, Mn, (proportional to the ratio between hydrodynamic and magnetostatic forces). More studies confirm this finding: Klingenberg and Zukoski (1990) and Goodwin et al. (1997). Although an increasing number of applications has been developed, like control of torquetransfer in clutches and rotary brakes, studies to unravel the correlation between the macroscopic behavior and microscopic structure of these systems are still necessary. When performing a rheological measurement, there are always solid boundaries against which fluid is intended to adhere, while neighboring fluid is set in Juan de Vicente Modesto T. López-López Juan D. G. Durán Fernando González-Caballero Shear flow behavior of confined magnetorheological fluids at low magnetic field strengths