# Study of Magnetorheological Grease's Thermomagnetic Coupling Rheology
## 1 Introduction  
Magnorheological grease is a colloidal dispersion system composed of magnetic particles and a lubricating grease matrix. Currently, the most commonly used magnetic particles are micron-sized carbonyl iron powders. Lubricating greases with different viscosity grades are selected as the matrix based on the viscosity requirements of practical working conditions. The base carrier fluid in the grease can prevent the sedimentation of magnetic particles [1, 2]. Under the action of an external magnetic field, the magnetic particles arrange themselves into a chain-like structure along the direction of the magnetic field due to the magnetic torque, giving rise to a magnetorheological effect in the magnetorheological grease. The thickening agent in the grease causes the magnetorheological grease to exhibit non-Newtonian flow characteristics [3]. Owing to its remarkable sedimentation stability and magnetorheological effect, magnetorheological grease holds significant research value and promising application prospects. Researchers both domestically and internationally have primarily focused on the preparation and rheological properties of magnetorheological grease. [PERSON] et al. [4, 5, 6, 7] investigated the influence of differently shaped magnetic particles on the rheological properties of magnetorheological grease and found that plate-like particles exhibited superior yield stress and magnetorheological effects. [PERSON] et al. [8, 9] studied the effects of different timings of magnetic particle addition and cooling conditions on the performance of magnetorheological grease. The research results indicated that adding magnetic particles duringthe dilution stage improved the stability and flowability of magnetorheological grease, and faster cooling rates resulted in lower grease consistency. [PERSON] et al. [10] investigated the effect of temperature and magnetic field on the rheological properties of magneto-rheological grease and showed that the apparent viscosity of magneto-rheological grease became less affected by temperature after the application of the magnetic field. [PERSON] et al. [11] proposed a simulation model based on machine learning methods, which was then compared with experimental results. The comparison between rheological data and experimental data demonstrated good accuracy. [PERSON] et al. [12] prepared magnetorheological grease with different mass fractions of hydroxyl iron powder and studied the variation in rheological parameters with shear rate and magnetic field intensity. The results showed that the magnetorheological grease prepared with hydroxyl iron powder exhibited excellent settling stability, and MRG-70 had an outstanding magnetorheological effect at a saturated magnetization intensity. [PERSON] et al. [13] investigated the normal force characteristics of a prepared magnetorheological grease and found that the normal force gradually increased with increasing temperature, mass fraction of the magnetic particles, and magnetic field intensity. [PERSON] et al. [14; 15] studied the thermal-magnetic coupling shear stability of prepared magnetorheological grease and observed that as the magnetic field intensity increased, the formation of magnetic chains among the magnetic particles in the magnetorheological grease affected its rheological performance, resulting in good shear stability. In addition, foreign scholars have carried out some research on the thermal effect of nanofluids. [PERSON] et al. [16] proposed a Cu-Al\({}_{2}\)O\({}_{3}\)/water hybrid nanofluid with the Darcy-Forchheimer effect and studied the local Nusselt number and skin friction, which were predicted by an artificial neural network under different temperatures and speed conditions. [PERSON] et al. [17] proposed a numerical study on the heat and mass transfer characteristics of a non-Newtonian Williamson nanofluid over a stretching/shrinking sheet, considering thermophoresis and Brownian effects.