Design of a yield stress characterizing platform for magnetorheological fluid magnetized by permanent magnets

In this paper we proposed a platform for measuring shear force of magnetorheological (MR) fluid by which the relationship of yield stress and magnetic flux density of specific materials can be determined. The device consisted of a rotatable center tube placed in a frame body and the magnetic field was provided by two blocks of permanent magnets placed oppositely outside the frame body. The magnitude and direction of the magnetic flux were manipulated by changing the distance of the two permanent magnets from the frame body and rotating the center tube, respectively. For determining the magnetic field of the device, we adopted an effective method by fitting the finite element method result to the measured one and then rebuilt the absent components to approximate the magnetic field, which was hardly to be measured as different device setup were required. With the proposed platform and analytical methods, the drawing shear force and the corresponding yield stress contributed by MR fluid in respect to the magnitude and direction of given magnetic flux density could be evaluated effectively for specific designing purposes without the requirement of a large, complex, and expensive instrument.