Abstract
This paper investigated the effects of silicone oil viscosity (SOV) and carbonyl iron particle (CIP) weight fraction and size on dynamic yield stress for magnetorheological (MR) grease. The MR grease samples were prepared using orthogonal array L9 on the basis of a new preparation technology. The shear rheological tests were undertaken using a rotational shear rheometer and yield stress was obtained based on the Bingham fluid model. It was found that CIP fractions ranging from 65 wt% to 75 wt% and SOV varying from 50 m2·s−1 to 1000 m2·s−1 significantly affect the magnetic field-dependent yield stress of MR grease, but the CIPs with sizes of 3.2–3.9 μm hardly had any influence based on the analysis of variance (ANOVA). In addition, the yield stress of MR grease mainly depended on the CIP fraction and SOV by comparing their percent contribution (PC). It was further confirmed that there were positive effects of CIP fraction and SOV on yield stress through response surface analysis (RSA). The results showed a high dynamic yield stress. It indicated that MR grease is an intelligent material candidate which can be applied to many different areas requiring high field-induced rheological capabilities without flow for suspension. Moreover, based upon the multivariate regression equation, a constitutive model was developed to express the function of the yield stress as the SOV and fraction of CIPs under the application of magnetic fields.
Highlights
Magnetorheological (MR) fluids are smart materials whose rheological properties can be changed significantly, rapidly, and adjustably under the application of magnetic fields [1]
The results indicated the carbonyl iron particle (CIP) fraction and silicone oil viscosity (SOV) generated a synergistic effect on the yield stress in the MR grease
Experimental tests for the MR grease samples were conducted under different magnetic fields by using rotational rheometry
Summary
Magnetorheological (MR) fluids are smart materials whose rheological properties can be changed significantly, rapidly, and adjustably under the application of magnetic fields [1]. MR fluid has attained widespread attention owing to its excellent magnetic field-induced rheological performances in many applications, such as clutches, brakes, dampers, and shock absorbers requiring active intelligent control for torque transmission or vibration [2,3]. In order to solve this settling in the MR fluid, various means have been developed; adding thxiotropic agents and surfactants to form a thixotropic network and enhance antisettling hydrodynamic effects [4,7,8,9]; coating the magnetic particles with polymers to decrease density [1]; and adding magnetic nanoparticles to produce steric repulsion between the micron-scale carbonyl iron particles (CIPs) [10]. Many researchers have made great efforts in this area, the problem of settlement stability for MR fluids is not fully
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