Influence of Kinematic Viscosity of Base Oil on Magnetorheological Grease

doi:10.1007/s12204-022-2438-1

Abstract

Abstract: In order to explore the effect of kinematic viscosity of base oil on the rheological properties of magnetorheological (MR) grease, MR grease samples containing 70% (mass fraction) carbonyl iron powder and carrier liquid separately with kinematic viscosity of 10 mm2/s, 100 mm2/s, 350 mm2/s and 500 mm2/s were prepared. The influence of kinematic viscosity of carrier liquid on the settlement performance of MR grease was analyzed. The rheological properties of MR grease were tested and analyzed under steady-state shear and oscillatory shear modes. The results show that the kinematic viscosity of base oil has a significant effect on the settling stability of MR grease. The zero-field viscosity of MR grease increases with the increase of the kinematic viscosity of the base oil, and the sedimentation performance is better. The colloid stability of MR grease is poor after the kinematic viscosity of base oil is lower than a threshold, and static oil bleed will occur immediately. In addition, the shear stress of MR grease increases with the increase of magnetic induction. When the shear rate is less than 10 s?1, the shear stress increases rapidly with the increase of shear rate. When the shear rate further increases, the shear stress tends to a stable value. The reason is that the thickener fibers in MR grease are subjected to the shear stress between laminar flows, the entanglement occurs, which makes MR grease exhibit shear thinning, and its rheological properties conform to the Herschel-Bulkley constitutive model. In the process of preparation, some carbonyl iron powder will be embedded into the thickener fiber, which shows different magnetic saturation phenomena due to shear thinning under steady-state shear and oscillatory shear.

Key words: magnetorheological (MR) grease, Herschel-Bulkley, steady shear, oscillatory shear

摘要： 为了获得低零场黏度且抗沉降性能优异的磁流变脂，制备了羰基铁粉质量分数为70%，基础油运动黏度分别为10 mm2/s、100 mm2/s、350 mm2/s和500 mm2/s的复合锂基磁流变脂（MR grease）。研究了基础油运动黏度对MR grease沉降稳定性的影响，并在稳态剪切和振荡剪切的模式下测试分析了MR grease的流变特性。结果表明，基础油的运动黏度对MR grease的沉降稳定性有明显影响，即基础油的运动黏度越大，所制备的MR grease的零场黏度越大，沉降稳定性越好。此外，MR grease的剪切应力随磁感应强度的增强而增大；当剪切速率小于10 s-1，MR grease的剪切应力随剪切速率的增加而迅速增大，进一步增大剪切速率时，剪切应力趋于一稳定值。由于MR grease中稠化剂纤维受到层流间剪切应力的作用，发生解纠缠使得MR grease表现出剪切稀化现象，其流变特性符合赫谢尔-巴尔克莱本构模型。制备过程中部分羰基铁粉会嵌入到稠化剂纤维中，在稳态剪切和振荡剪切状态下由于剪切稀化的作用显示出不同的磁饱和现象。

关键词: 磁流变脂，赫谢尔-巴尔克莱模式，稳态剪切，振荡剪切

CLC Number:

O373

WANG Wenchao (王文超), ZHANG Guang (张广),WANG Huiaing (汪辉兴)，YEXudan(叶绪丹)，WANG Jiong*(王炅). Influence of Kinematic Viscosity of Base Oil on Magnetorheological Grease[J]. J Shanghai Jiaotong Univ Sci, 2023, 28(5): 676-685.

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