Temperature dependency of magnetorheological fluids' properties under varying strain amplitude and rate

The temperature dependencies of the rheological and viscoelastic properties of magnetorheological (MR) fluids were investigated experimentally using a rotary rheometer. The shear flow and oscillatory shear strain experiments were conducted over a wide temperature range (-5 to 50 degrees C) for different levels of magnetic flux density, and strain amplitude and rate. The temperature effect is also investigated considering three different MR fluids with varying solid particles concentration. The measured shear stress-strain data were used to evaluate the effects of temperature and magnetic field on the pre- and post-yield properties of the MR fluids. The acquired data under harmonic strain excitations swept in the 0.005-100% strain amplitude and different levels of steady temperatures in the -5 degrees C to 50 degrees C range were analyzed to identify storage and loss moduli as functions of the temperature, shear strain amplitude and frequency. The results suggested strong influence of temperature on the mechanical properties of the fluids in the absence of the magnetic field, especially at temperatures below 10 degrees C. The magnetic field, however, constituted the dominant effect. In the presence of a magnetic field, the temperature effect could be observed only at low strain levels. The temperature dependency of the mechanical properties also varied considerably with the iron particle fraction of the MR fluid. The critical strain amplitude also increased with increasing magnetic field density, while the linear storage modulus approached saturation with magnetic flux density above 0.2 T.