Mechanical properties analysis of magnetorheological fluids considering the stability of microstructure under squeezing shear action

Currently, squeezing strengthening is an effective approach to address the issue of inadequate transmission torque in magnetorheological transmission systems. However, during the squeezing process, the chain formation process of the magnetic particles inside magnetorheological fluids is very complex, and the mechanism by which the increase in shear yield stress occurs remains unclear. Therefore, it is very necessary to study the microstructure and macroscopic mechanical properties of the magnetorheological fluid under the combined effects of squeezing and shear. Firstly, the energy at the break position of the magnetorheological fluid’s magnetic particle chain under the action of shear is analyzed, and a simulation model of the magnetic particle chain is established to analyze the magnetic induction intensity of the magnetic particle chain and the force between magnetic particles. Subsequently, the influence of the magnetic wall effect on the magnetic particle chain under squeezing is examined, and the dynamic equation governing the behavior of magnetic particles in the presence of the magnetic wall effect is derived. Building on the preceding analysis, models for the microstructure and macroscopic mechanical properties of magnetorheological fluid under the combined effects of squeezing and shear are developed. The resulting shear yield stress is then compared with experimental results to validate the established model. The shear yield stress model under squeezing is compared with the conventional squeezing strengthening model, and the impact of the volume fraction of magnetorheological fluid on the macroscopic mechanical properties is analyzed. The results show that the shear yield stress model presented in this paper can accurately determine the position of the magnetic particle chain fracture and effectively reflect the microstructural stability of the magnetic particle chain in the presence of the magnetic wall effect. Compared to the traditional model, it aligns more closely with the experimental results. The shear yield stress of the model established in this paper is 108.8 kPa at a volume fraction of 20 %. When the volume fraction is increased to 35 %, the shear yield stress rises to 129.8 kPa, representing an increase of 19.3 %. The shear yield stress of the traditional squeezing model is 106.7 kPa at a volume fraction of 20 %. Upon increasing the volume fraction to 35 %, the shear yield stress rises to 119.9 kPa, reflecting an increase of 12.4 %. As the volume fraction of magnetic particles increases, the growth rate of shear yield stress in the model presented in this paper surpasses that of the traditional squeezing model. Furthermore, the increasing trend of shear yield stress in this model more accurately reflects actual conditions.