<title>Viscoelastic properties of MR fluids under oscillatory shear</title>

Abstract

In this paper, viscoelastic properties of MR fluids under oscillatory shear were experimentally studied using a rheometer with parallel-plate geometry. The experiments were conducted with amplitude sweep mode and frequency sweep mode. For the amplitude sweep mode, the driving frequency is fixed at a given value of (omega) rad/s and the strain amplitude, (gamma) 0, is swept from 0.01% to 100$; For the frequency sweep mode, the strain amplitude is fixed at a certain strain, (gamma) 0, and driving frequency is swept from 1 to 11 Hz. Consequently, the effects of strain amplitude, frequency, magnetic field strength, and temperature on the viscoelastic properties of MR fluids were investigated. MR fluid behaves as a linear viscoelastic body for sufficiently small strain amplitude ((gamma) 0 (gamma) lin). At small strain amplitudes, the storage modulus and the loss modulus are independent of strain amplitude. At high strain amplitudes, the storage modulus is independent of the frequency and approaches plateau values at low frequencies. With increasing frequency, the storage modulus shows a decreasing trend before increasing again. The loss modulus varies slightly with frequency. MR fluid shows elastic-dominated properties in a magnetic field. Both the storage modulus and the loss modulus increase significantly with increasing field of strength. The temperature dependence of viscoelastic properties is also discussed. For the experimental temperature range of 20 degree(s)C to 60 degree(s)C, the storage modulus shows a slightly decreasing trend with temperature.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.