Mechanical properties of magnetorheological fluids under squeeze-shear mode

Abstract

Magnetorheological (MR) fluids is very promising intelligent materials and it can rapidly by changed from a liquid state to a solid state in a magnetic field. Various industries are full of potential MR fluids applications, but current MR fluids have the limitation that their yield stresses are not strong enough to meet some industrial requirements. The crucial problem is how to enhance the yield stress of MR fluids. Electrorheological (ER) fluids, similar to MR fluids, can be achieved high strength under squeeze mode, which proposed a method to achieve high-efficiency MR fluids by study of shear after compression. The performance of MR fluids under squeeze-shear mode was inveatigated. Magnetic fields being generated by two coils carrying different magnitudes of DC electrical current were applied on the MR fluids when shearing after compression were carried out on a self-constructed test system. For each trail the current in the coil and the compressive force were kept constant and the instantaneous yield stress was recorded. The relations of compression stress versus compression strain, yield stress versus compression stress were studied under different applied currents. The ploting of compressive stress against compressive strain has been observed to have three regions: the first and third regions has a linear relationship and the second region has a zero increasing. The slope of the curve was found to be larger when the applied current was larger. The SG MRF2035 without compression process has a yield stress about 53kPa at most even if increasing the applied current. But after compression, the yield stress increase with the increasing compressive stress under the different applied currents. And some promising results are obtained, for example, when the applied current is 2.5A and the compressive stress is 2.0MPa, the yield stress exceeds 1100kPa. It showed that the yield stress of MR fluids after compression was much stronger than that of uncompressed MR fluids under the same applied current. The enhanced yield stress of MR fluids can be utilized to design the MR clutch and brake for new structure and will make MR fluids technology attractive for many applications.