# Study of the Effect of Continuous Thermal Effects on the Shear Stability of Magnetheological Grease
## 3 Results and Discussion
### Rheological Properties in Oscillatory Shear Mode  
Figure 7 shows the strain scanning curves of magnetorheological grease at different magnetic field strengths and temperatures. At low shear strain, the energy storage modulus G' of the magnetorheological grease was higher than the loss modulus G\({}^{\prime\prime}\) at all magnetic fields and temperatures, which indicates that the external force at low shear strain is insufficient to overcome its own solid properties [23]. With the increase in the shear strain, the energy storage and loss modulus curves of the samples under different experimental conditions gradually converged, which indicates that the solid properties of the magnetorheological grease change under high shear strain, and the flow properties become better. The energy storage modulus of 00#MRG changed significantly with the increase in the magnetic field strength at different temperatures, which implies that the magnetic field can effectively enhance the self-resistance of the magnetorheological grease, namely, a larger external shear strain is needed to change its solid properties. Sample 1#MRG had a close amplitude of change in the shear strain curve at each temperature gradient, indicating that the higher-consistency magnetorheological grease is less affected by magnetic field changes and more resistant to temperature changes. Figure 8 shows the frequency scanning curves of the magnetorheological grease at different magnetic field strengths and temperatures. Smaller changes in energy storage and loss modulus of 00#MRG at lower experimental temperatures indicates that the external force applied to the magnetorheological grease is insufficient to overcome its own solid properties within the test frequency range, and higher shear strain is required in order to improve the fluidic properties of the magnetorheological grease. At 80 \({}^{\circ}\)C, the storage energy and loss modulus changed more drastically at low shear frequency because the high temperature induces the disentanglement and reorganization of the soap fiber structure in the magnetorheological grease [24; 25] and some of the magnetic particles can be released to  
Figure 7: Strain scanning curves of MRG: (**a**) 00#MRG, (**b**) 0#MRG, (**c**) 1#MRG. form a columnar or cluster structure under the action of the magnetic field, which in turn enhances the strength of the composite structure of the magnetorheological grease [26]. Moreover, the variation of energy storage and loss modulus of 1#MRG under each magnetic field and temperature gradient in the shear frequency scan is small, which is similar to the experimental results of shear strain in the dynamic mode, indicating that the continuous phase with a high consistency has great application prospects under severe working conditions with large temperature rise variations, and it can effectively reduce the problem of inadequate lubrication caused by high temperatures. Combined with the analytical results of steady state experiments, the magnetorheological grease with a higher degree of entanglement possesses better shear stability under the complex working condition of thermomagnetic coupling. According to the research of [PERSON] et al. [27], the entanglement degree of magnetorheological grease can be characterized by the platform modulus (\(\mathrm{G}_{\mathrm{N}}^{0}\),Pa). Furthermore, the platform modulus of magnetorheological grease can be derived directly from frequency scanning experimental data through extrapolation, as shown in Equation (2):  
\[\mathrm{G}_{\mathrm{N}}^{0}=\left[\mathrm{G}^{\prime}\right]_{\tan\delta\to \mathrm{minimum}} \tag{2}\]  
where \(\tan\delta\) is the loss factor. Equation (2) indicates that the value of the platform modulus of the magnetorheological grease is equal to the value of the energy storage modulus of the magnetorheological grease when the loss factor is minimized. Figure 9 shows the variation curves of the platform modulus of each sample under different magnetic fields.