# Study of Magnetorheological Grease's Thermomagnetic Coupling Rheology
## 4 Results and Discussion
The reduction in the viscosity of magnetorheological grease after reaching saturation magnetization was attributed to its shear thinning effect. In Figure 5, the change in the viscosity of magnetorheological grease with the shear rate at different temperatures is depicted. It is observed from the graph that the viscosity of magnetorheological grease decreased gradually with the increase in shear rate, indicating a shear thinning phenomenon. Without a magnetic field, the viscosity of magnetorheological grease decreased gradually with increasing temperature. This could be attributed to the decrease in the entanglement degree of soap fibers within the magnetorheological grease, allowing the base oil to flow out more easily and resulting in viscosity reduction. At the same temperature, with the enhancement of magnetic field intensity, the apparent viscosity of the magnetorheological grease increased progressively. At 60 \({}^{\circ}\)C, the apparent viscosity of the magnetorheological fluid showed a relatively small increase with increasing magnetic field strength. It was observed that at 440 mT, the apparent viscosity of the magnetorheological fluid was the lowest compared to 20 \({}^{\circ}\)C, 40 \({}^{\circ}\)C, and 80 \({}^{\circ}\)C. This phenomenon can be primarily attributed to the reduced entanglement of soap fibers within the magnetorheological fluid at 60 \({}^{\circ}\)C due to the elevated temperature, resulting in a decrease in apparent viscosity compared to 20 \({}^{\circ}\)C and 40 \({}^{\circ}\)C. Furthermore, although the entanglement degree of soap fibers within the magnetorheological fluid decreased at 60 \({}^{\circ}\)C compared to 80 \({}^{\circ}\)C, the residual entanglement structure inhibited the chain formation behavior of magnetic particles, leading to a reduction in apparent viscosity. Conversely, at 80 \({}^{\circ}\)C, the entanglement degree of soap fibers within the magnetorheological fluid reduced significantly, resulting in a significant increase in the quantity of chain-formed magnetic particles, and consequently, an increase in apparent viscosity [15]. Figure 5: Magnetorheological grease apparent viscosity curve. The flow characteristics of magnetorheological grease under varying temperatures and magnetic fields are shown in Figure 6. The graph indicates a gradual decrease in shear stress during the pre-shear stage as the temperature increased. This behavior can be attributed to the non-Newtonian properties of the grease, which result in a nonlinear increase in shear stress with higher shear rates. Notably, increasing magnetic field intensity led to a more pronounced increase in shear stress within the magnetorheological grease. It can be noted from the figure that the shear stress at 60 \({}^{\circ}\)C was disorganized as the shear rate changed. This was because the degree of entanglement of soap fibers in magnetorheological grease decreased at 60 \({}^{\circ}\)C. The shear stress was supported by soap fibers and magnetic chains, and the disorganization phenomenon occurred due to the obstruction of soap fibers in the chain formation process [26]. At elevated temperatures (80 \({}^{\circ}\)C), the disruption phenomenon of shear stress within the grease became less evident. This observation can be primarily attributed to the comparatively higher concentration of magnetic particles. When subjected to an external magnetic field, numerous magnetic chains were formed, exhibiting a certain level of structural strength. As the magnetic field intensity strengthened, the clustered magnetic chains progressively increased in structural integrity, reaching maximum strength at the saturation magnetization intensity. Consequently, this resulted in an increasing damping force throughout the shearing process, peaking at the saturation magnetization intensity. The graph further reveals that within a specific range of shear rates, the shear stress of the grease remained relatively constant.