热磁耦合作用下磁流变脂剪切稳定性及其机理

磁流变器件内部介质均面临热磁耦合、频繁剪切等复杂工况，剪切稳定性是磁流变介质实现持久服役的重要指标。本文以实验室制备的磁流变脂为研究对象，基于流变学、磁学性能分析结果探究了热磁耦合作用下磁流变脂剪切稳定性变化规律及其机理。研究结果表明，温度和磁场强度发生变化时，磁流变脂流变性能也发生了较为显著的变化。触变性分析与连续剪切结果显示热磁耦合作用下磁流变脂总体保持着较好的剪切稳定性，基载液润滑脂皂纤维结构和磁链的交互作用将会对磁流变脂剪切稳定性产生影响。在较低温度、较弱磁场强度下，皂纤维结构是磁流变脂流变学性能影响的主导因素，剪切稳定性良好；在较高温度、较强磁场强度下，皂纤维缠结程度降低而磁链强度增强，磁链结构在磁流变脂流变学性能影响中占主导因素，剪切稳定性良好；在从皂纤维影响占主导变化为磁链影响占主导过程中，皂纤维剪切破坏时磁性颗粒被释放出来，因磁场的影响，磁性颗粒无法及时分散至皂纤维内部，最终致使磁流变脂剪切稳定性变弱。

Shear stability and mechanism of magnetorheological grease under thermo-magnetic coupling

The internal media of magnetorheological (MR) devices are faced with complex working conditions, such as thermo-magnetic coupling, frequent shearing and so on. Shear stability is an important indicator to evaluate the durable service of MR medium. In this work, an experimental study was conducted to investigate the change law and mechanism of the shear stability of the MR grease prepared in the laboratory under the thermo-magnetic coupling by analyzing the rheology and magnetic properties. The results showed that the rheological properties of MR grease changed significantly when the temperature and magnetic field intensity change. The results of thixotropy analysis and continuous shear indicated that MR grease maintained favorable shear stability under the thermo-magnetic coupling effect. The interaction of the soap fiber structure of carrier grease and magnetic linkage affected the shear stability of MR grease significantly. At relative low temperature and comparative weak magnetic field, the structure of soap fiber was the main factor affecting the rheological properties of MR grease. At higher temperature and stronger magnetic field strength, the entanglement degree of soap fiber decreased and the magnetic linkage became strengthened. The magnetic linkage structure played a dominant role in the rheological properties of MR grease. Besides, the MR grease represented favorable shear stability under above both conditions in this work. The shear stability of MR grease finally became weaken during the process of dominant factor converted from the soap fiber to the magnetic linkage for two reasons: the magnetic particles were released while the shear failure of soap fiber and they cannot be dispersed in time due to the influence of magnetic field.