In order to study the chain-forming process of magnetic-rheological fluid(MRF)and the influence factors of its shear stress,microscopic observations were made to the magnetic-rheological fluid prepared with carbonyl iron powders as ferromagnetic particles and dimethyl silicon oil as carrier fluid and shear stress tests were carried out by using Rheometer Physica MCR 301.The results indicate that the shear stress increases significantly with the increase of shear rate,volume ratio and magnetic field strength...