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After long-term operation of the magnetorheological(MR) damper, wear and aging of seals are inevitable, resulting in leakage of magnetorheological fluid. Due to the small gap at the location of the leakage, the percentage of silicone oil in the leaked liquid is significantly increased. The shear stress of the concentrated MR fluid under the magnetic field will change significantly, which will directly affect the accuracy of damping. The expression of Bingham model is simple and widely used in the design of MR damper. However, when the percentage of silicone oil in MR fluid is reduced to near solid state, the Bingham model which is originally suitable for fluid will not be able to accurately describe it. The applicable boundary of Bingham model between fluid and solid state is not clear. In order to clarify the applicable boundary of the Bingham model and expand the range of application, this paper takes the percentage of silicone oil in MR fluid as the research object. The Bingham model was modified to describe the effect of silicone oil percentage on shear stress. This is even applicable to near-solid MR fluids. MR fluids with different silicone oil percentages were tested by rheometer. The test results show that the percentage of silicone oil has a significant effect on the viscosity term of the model. The Bingham model containing the percentage of silicone oil has higher accuracy and wider application range. This study contributes to the establishment of an integrated calculation model of MR damper, magnetic powder damper or magnetic powder brake.

Magnetorheological fluid,Near solid state,Viscous damping,rheology,Bingham model