Yield dimensionless magnetic effect and shear thinning for magnetorheological grease

Abstract

The effects of silicone oil viscosity (SOV), carbonyl iron particles (CIPs) weight fraction and size on the yield dimensionless magnetic effect (DME) and shear-thinning behavior for magnetorheological (MR) grease were experimentally investigated in this study. Nine MR greases were prepared using Taguchi L9 orthogonal array based on an unconventional synthesis technique. The yield DME, namely the controllability of magnetic effect relative to viscous effect under the on-state magnetic fields and zero shear rate, was observed to be closely related to CIPs fraction based upon significance assessment and percent contribution (PC) comparison, whereas the shear-thinning behavior of suspension was dependent on the CIPs fraction and SOV. According to the analysis of discrepancy direction at the presence of magnetic fields, there was a negative linear correlation between yield DME and CIPs fraction, but the shear thinning had positive linear correlation with the CIPs fraction and SOV. Furthermore, the PC and the corresponding actual contribution values (ACV) of SOV and CIPs fraction towards the shear thinning showed distinct characteristics which were relevant to the critical magnetic fields. This study presented a hypothesis in which the difference of relative evolution rate between fiber structures and magnetic constructions under shearing and different magnetic fields caused the differences of PC and ACV of SOV and CIPs fraction to suspensions-viscosity attenuation.