Study of the Effect of Continuous Thermal Effects on the Shear Stability of Magnetorheological Grease

Abstract

Magnetorheological dampers in the service of the medium in a project experience continuous thermal effects, frequent reciprocating shear and other complex conditions. Shear stability is an important indicator of the reliability of a magnetorheological media service. Magnetorheological grease (MRG) was prepared using hydroxy iron powder with a mass fraction of 30% and lithium grease of different consistency grades as a continuous phase. The results of magnetic and rheological properties analysis were combined to investigate the mechanism of the continuous thermal effect on the shear stability of MRG. The results show that changes in the temperature field and magnetic field cause significant changes in the magnetic and rheological properties of MRG. At low temperatures and low magnetic fields, the soap fiber structure unique to MRG can effectively inhibit the movement of magnetic particles, with slight changes in the rheological properties and excellent shear stability. When the temperature increases to 80 °C, 00#MRG is damaged by the high temperature. The soap fiber structure is fractured and reorganized, and the rheological properties change significantly. However, the rheological properties of 1#MRG remain largely unchanged during the magnetic field enhancement to saturation, showing better shear stability. The higher consistency continuous phase has excellent heat resistance and better shear performance stability in the face of thermomagnetic coupling conditions, but the fiber breakage caused by continuous reciprocating shear poses a challenge to the service stability of MRG.

1. Introduction

Magnetorheological fluid (MRF) is a kind of intelligent material that can achieve millisecond-level, solid–liquid reversible changes by adjusting the magnetic field strength, and full lubrication in the working area can be achieved by controlling the magnetic field, overcoming the problem of insufficient adhesion with the cavity wall when the conventional grease encounters a temperature rise. It has great prospects in magnetorheological apparatus applications, such as vibration dampers, clutches, and transmission mechanisms [1]. However, the magnetorheological grease (MRG) device has a settling problem during service, which restricts the application and development of related magnetorheological devices. Magnetorheological grease uses grease as a continuous phase matrix, and grease is a structured colloidal dispersion system with a unique soap fiber structure that can greatly improve the settlement problem of magnetic particles [2,3]. Additionally, magnetorheological devices are subject to temperature increases due to internal friction during frequent shearing, and changes in the operating temperature have a great impact on the rheological properties of magnetorheological grease.

At present, the domestic and international research on magnetorheological grease mainly focuses on the study of its rheological properties by focusing on its components, additives and preparation methods. Wang et al. [4] found by employing steady-state shear test experiments on the content of carbonyl iron powder in magnetorheological grease that, within a certain range, the higher the content of hydroxy iron powder in magnetorheological grease, the wider the adjustable range of shear viscosity and shear stress in the steady-state shear mode. Sahin et al. [5] found that temperature had a significant effect on the field-induced yield stress of magnetorheological grease based on the temperature-sensitive properties of the grease components in magnetorheological grease by analyzing the rheological properties of magnetorheological grease with different temperatures and magnetic fields. Kim et al. [6] investigated the rheological properties of soft carbonyl iron particles by adding additives to magnetorheological grease and found that the shear viscosity versus shear rate profile of magnetorheological grease was greatly reduced with the addition of 5 wt% kerosene at the same magnetic field strength. Hu et al. [7] found that by adjusting the thickener content in magnetorheological grease, the magnetorheological effect could be effectively improved and its magnetic properties could be enhanced through experiments on the magnetorheological properties of magnetorheological grease. He et al. [8] analyzed the magnetic particle size in magnetorheological grease by building a body-centered columnar model and found that the magnetorheological grease shear yield stress increased faster with increasing particle size when the particle size was within a certain range. Mohamad et al. [9,10,11] investigated the magnetic field-dependent rheological properties of magnetorheological grease in continuous shear and oscillatory shear modes by means of platelike carbonyl iron particles and found that platelike particles have higher apparent viscosity relative to spherical particles due to the larger surface contact area of the particles, which resulted in a strong magnetic moment interaction between the particles. Magnetorheological grease consisting of platelike magnetic particles had a lower energy storage modulus relative to spherical particles. Wang et al. [12] found through experiments on the magnetic particle content of magnetorheological grease that the yield stress of magnetorheological grease was highly correlated with the particle content, and the magnetic field greatly weakened the shear rate correlation at the maximum yield stress of magnetorheological grease as the content of magnetic particles increased. Magnetorheological devices in the service process experience continuous shear, continuous thermal effects, and other aspects that impact the magnetorheological media during the long-term service process for shear stability.

Based on this, magnetorheological greases with different consistency grades were experimentally prepared. MCR–301 was used to conduct experiments on the magnetic and rheological properties, aiming to investigate the influence of a continuous thermal effect on the shear stability of the magnetorheological grease. By combining the magnetic results and the rheological results, the influence law of the thermal effect on the magnetorheological grease was analyzed. We conducted a detailed examination of the performance variations of magnetorheological grease when subjected to thermomagnetic coupling conditions, which involves integrating the magnetorheological effect with the soap fiber structure system of the grease. Our aim is to establish a theoretical foundation and gather experimental data to aid in the design and advancement of magnetorheological grease devices.

2. Materials and Methods

2.1. Experimental Materials

The magnetic particles used in the experiment were MRF–15 carbonyl iron powder with an average diameter of 3–5 mm, which were from Jiangsu Tianyi Ultrafine Metal Powder Co. (Huai’an, China). The grease was general lithium grease from Sinopec Lubricants Co., Ltd., Tianjin Branch (Tianjin, China), and the magnetorheological grease was prepared using the consistency grades of 00, 0, and 1, and its main contents are shown in

Table 1. Main elements of magnetorheological grease (MRG) in different continuous phases.

Properties	Details
Numbering	00#MRG	0#MRG	1#MRG
Types of thickeners	Lithium 12–hydroxystearate
Base oil	Mineral oils
Consistency grade	00	0	1
Working taper/0.1 mm	400–430	355–385	310–340
Appearance at room temperature	Fluid	Semi–fluid	Soft–solid

. The specific preparation method was combined with the method proposed by Mohamad et al. [11]; first, the grease was preheated for a certain period of time, and then carbonyl iron powder with a mass fraction of 30% was added; stirring continued at a constant temperature, and the magnetorheological grease samples were obtained after cooling.

2.2. Rheological Property Testing

The rotational rheometer Physica MCR–301 from Anton Paar, Berlin, Germany (Figure 1), was used to conduct experiments on the rheological properties of magnetorheological grease in rotational shear mode and oscillatory shear mode. The test rotor of the rheometer was PP20/MRD, and the clearance between the rotor and the test platform was 1 mm; the magnetic field control module was PS–MRD, and the temperature control module was VISCOTHERMVT2.

We conducted magnetic field scanning tests, thixotropy tests, and apparent viscosity tests using rotary shear mode. The specific test parameters were as follows: for the magnetic field scanning test, the shear rate was set to 10 s⁻¹, and the magnetic induction strength ranged linearly from 0 mT to 1100 mT (1 A current in the rheometer equaled 220 mT magnetic induction strength); in the thixotropy test, the shear rate initially increased from 0.01 s⁻¹ to 100 s⁻¹ and then decreased from 100 s⁻¹ to 0.01 s⁻¹; and for the apparent viscosity test, the shear rate was fixed at 100 s⁻¹.

In the oscillatory shear mode, experiments were conducted to examine the effects of frequency and strain amplitude. The frequency scanning test involved controlling the shear frequency from 1 rad/s to 100 rad/s with a fixed strain amplitude of 0.1%. Conversely, the strain scanning test maintained a constant shear frequency of 1 Hz while varying the strain amplitude from 0.01% to 100%. The experiments were conducted under different magnetic induction strengths (55, 110, 220, and 440 mT) and temperatures (20, 40, 60, and 80 °C).

3. Results and Discussion

3.1. Analysis of Magnetic Properties

Figure 2 shows the magnetic field scanning curves of the magnetorheological grease at different temperatures. It was evident that the shear stress of each magnetorheological grease sample rose as the magnetic induction strength was increased and gradually stabilized after the magnetic field strength reached 440 mT, at which point the magnetorheological grease achieved magnetization saturation. The magnetic field strength at magnetization saturation of the magnetorheological grease varied less with increasing the continuous phase consistency grade, indicating that the consistency of the continuous phase has a limited effect on the magnetic properties of magnetorheological grease.

In addition, the magnetic field scanning curves of 00#MRG and 0#MRG were more discrete because the soap fibers of the continuous phase consistency grades are less entangled and the high temperature promotes the disentanglement of the soap fiber structure [13,14,15], which greatly mitigates the behavior of the soap fiber structure that impedes the motion of the magnetic particles. It is shown that the sustained thermal effect has a large influence on the rheological properties of magnetorheological grease. Sample 1#MRG had a smaller dispersion, which may indicate that the magnetorheological grease with higher-consistency grease as the continuous phase has better thermal stability. Therefore, in order to further investigate the mechanism through which magnetorheological grease is affected by the continuous thermal effect, it is necessary to discuss it in conjunction with the rheological experiments under a constant magnetic field.

Figure 2. Magnetic scanning curves of MRG at different temperatures.

Figure 2. Magnetic scanning curves of MRG at different temperatures.

Figure 3 shows a schematic diagram of the variation of magnetic domains of magnetic particles with the magnetic field. The highly entangled soap fiber structure, which is unique to lubricating magnetorheological grease, can effectively inhibit the settlement of magnetic particles, which is conducive to maintaining the stability of magnetorheological grease colloids [16,17,18]. According to the results of magnetic property analysis, the magnetic particles had a great influence on the rotational shear stress of the magnetorheological grease. In the absence of magnetic field excitation, magnetic particles mixed in lithium grease, the magnetic domain direction is nonisotropic [19]. The rheological properties of magnetorheological grease are mainly affected by the temperature change; under a lower magnetic field strength, the magnetic particles experience a rotational shear external force and the magnetic field, the magnetic particles move violently, and the direction of the magnetic domain changes; with the gradual increase in magnetic field strength to the saturated magnetic field strength, the magnetic domain direction and the magnetic field direction are the same, and the magnetic particles break through the soap fiber structure of the block to form a magnetic chain. Although the soap fibers in the continuous phase of 1#MRG have a higher degree of entanglement, the magnetic particles encounter great resistance to movement, resulting in better shear stability of the magnetorheological grease colloids.

3.2. Rheological Properties in Rotational Shear Mode

Figure 4 shows the thixotropy curves of magnetorheological grease at different magnetic field strengths and temperatures. Thixotropy was a reversible solvation phenomenon, and the shear stability of the magnetorheological grease could be characterized by the dispersion of the thixotropy curves. The shear stress of each magnetorheological grease sample increased slowly at low shear rates, exhibiting a platform region, because the external force at low rates is not sufficient to overcome the composite structure composed of a soap fiber structure and magnetic chains.

Meanwhile, the shear stresses in the 00#MRG platform region varied greatly at different magnetic field strengths and reached a maximum at 80 °C, indicating that the magnetic chains greatly increase the shear resistance of the magnetorheological grease, and that the high temperature further unravels the structure of the soap fibers and accelerates the formation of magnetic chains. The dispersion of the thixotropy curves of 1#MRG under different magnetic field strengths and temperatures was lower compared with that of 00#MRG, indicating that the continuous phase with higher consistency provides better stability to the continuous shear condition. In order to deeply investigate the shear stability of magnetorheological grease at elevated temperatures, the effect of the continuous phase consistency grade on the shear thixotropy of magnetorheological grease is analyzed in conjunction with the thixotropic ring area.

Figure 4. Thixotropy curves of MRG: (a) 00#MRG, (b) 0#MRG, (c) 1#MRG.

Figure 4. Thixotropy curves of MRG: (a) 00#MRG, (b) 0#MRG, (c) 1#MRG.

Figure 5 shows the thixotropic ring area of the magnetorheological grease under different magnetic field strengths and temperatures. The area of the thixotropic ring was the area surrounded by the shear rate rise curve and the fall curve; the higher the overlap between the shear rate rise curve and the fall curve, the smaller the area of the thixotropic ring, which indicates that the material’s shear stability is better, and the material is stable under the complex working conditions. At the same temperature, the thixotropic ring area of 00#MRG showed a nonlinear increase with the increase in the magnetic field strength [20] because the degree of entanglement of the soap fibers of NLGI 00 lubricating grease is low, and the formation of the magnetic chain is less impeded, and the composite structure, which is gradually dominated by the magnetic field, has a greater effect on the shear resistance of the magnetorheological grease with the increase in the magnetic field strength. Under 440 mT, the thixotropic ring area of 00#MRG increased nonlinearly with temperature because the high temperature promotes the untangling of soap fibers and enhances the dominant role of the magnetic chain in the composite structure, which is manifested in the great size of the thixotropic ring area of 00#MRG under 440 mT and 80 °C. The fracture and reorganization of soap fibers are closely related to the shear motion of the magnetorheological apparatus. The degree of entanglement of soap fibers in the continuous phase of low consistency is low, and its soap fiber structure is less resistant to the magnetic chains that are gathered in large quantities due to the magnetic field, which is manifested as the destruction of the soap fiber structure due to the movement of the magnetic chains. Additionally, the medium in the mineral oil accounted for a high proportion, and a high temperature will cause the precipitation of mineral oil to a certain extent, causing great damage to the soap fiber structure, which in turn caused the soap fiber fracturing and reorganization.

In addition, the thixotropic ring area of 1#MRG was smaller under all experimental conditions because the soap fiber entanglement of NLGI 1 grease was high, the composite structure was dominated by the soap fiber structure during shear, and its operating temperature reached 120 °C. Therefore, the higher the consistency grade of the continuous phase in magnetorheological grease, the better the shear stability under complex working conditions involving continuous shear and continuous thermal effects.

Figure 5. Thixotropic ring area of MRG: (a) 00#MRG, (b) 0#MRG, (c) 1#MRG.

Figure 5. Thixotropic ring area of MRG: (a) 00#MRG, (b) 0#MRG, (c) 1#MRG.

Figure 6 shows the apparent viscosity curves and the average values of the apparent viscosities of magnetorheological greases at different magnetic field strengths and temperatures. Under the rotary shear mode, a fixed shear rate of 100 s⁻¹ was applied to the magnetorheological grease, and the viscosity did not change significantly with the shear time, which indicated that the three magnetorheological greases used in the experiments had better storage performances at low shear rates. According to the theory of fluid dynamics, the apparent viscosity of the grease was generated by internal friction, and the external force required to shear the soap fibers was the resistance to flow of the grease [21]. Magnetic particles agglomerating to form a magnetic chain under the action of a magnetic field require drastic changes caused by the temperature field and sustained shear, that is to say, the soap fiber structure suffers great damage, and then the apparent viscosity rises, and the magnetic chain becomes the dominant factor in the composite strength.

At the same temperature, the apparent viscosity of 00#MRG tended to increase with increasing magnetic field strength. Because number 00 lithium grease has lower soap fiber entanglement, the response to magnetic particles subjected to magnetic fields does not provide strong resistance. The apparent viscosity of 1#MRG, on the other hand, did not change much with temperature and magnetic field, which suggests that the continuous phase with a high degree of entanglement will greatly prevent the magnetic particles from being subjected to the movement of the magnetic field, and that the rheological properties of the high-consistency magnetorheological grease will be less affected by the thermomagnetic coupling field in the steady state mode. In order to further investigate the effect of magnetorheological grease subjected to a thermomagnetic coupling field in the dynamic mode, shear strain and frequency scanning experiments will be combined to analyze their effects of on its rheological properties.

Figure 6. Apparent viscosity curves and average values of apparent viscosity of MRG: (a) 00#MRG, (b) 0#MRG, (c) 1#MRG.

Figure 6. Apparent viscosity curves and average values of apparent viscosity of MRG: (a) 00#MRG, (b) 0#MRG, (c) 1#MRG.

In order to study the viscoelastic properties of magnetorheological grease in the dynamic mode, the complex modulus (G*, Pa) is introduced, which is described through Equation (1) [22].

$${\mathrm{G}}^{*}={\mathrm{G}}^{\prime }+\mathrm{i}{\mathrm{G}}^{″}$$

(1)

where G′ is the energy storage modulus characterizing the energy stored by the elastic deformation of the magnetorheological grease, Pa; i is an imaginary number; G″ is the loss modulus characterizing the energy lost by the viscous deformation of the magnetorheological grease, Pa; in addition, the ratio of the two of them, $\tan \mathsf{\delta }=\frac{{\mathrm{G}}^{″}}{{\mathrm{G}}^{\prime }}$, is known as the loss factor, which characterizes the extent of the loss of energy of the magnetorheological grease subjected to a shear movement with the magnitude of 1.

3.3. 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′ 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 °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 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.

Figure 8. Frequency sweep curves of MRG: (a) 00#MRG, (b) 0#MRG, (c) 1#MRG.

Figure 8. Frequency sweep curves of MRG: (a) 00#MRG, (b) 0#MRG, (c) 1#MRG.

According to the research of MARTIN-ALFONSO 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):

$$\begin{array}{c}{\mathrm{G}}_{\mathrm{N}}^0={\left[{\mathrm{G}}^{\prime }\right]}_{\tan \mathsf{\delta }\to \mathrm{minimum}}\end{array}$$

(2)

where $\tan \mathsf{\delta }$ 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. At a fixed 20 °C, the degree of entanglement of 00#MRG showed a steady increase with the increase in the magnetic field strength, because the lower viscosity of number 0 Lithium grease showed signs of shear thinning under continuous shear [28], the soap fiber structure is insufficient to inhibit the movement of magnetic particles under the excitation of the magnetic field, which leads to the formation of a columnar magnetic chain, and the composite structure composed of the magnetic chain and the soap fibers effectively enhances its own strength. The platform modulus of 1#MRG at a lower magnetic field was larger than that of 00#MRG, which is due to the fact that when the magnetic field strength is weaker, the magnetic particles aggregate to form a smaller scale of magnetic chains, and the soap fiber structure with the higher degree of entanglement of number 1 lithium grease creates a great resistance to the movement of magnetic particles, and the magnetorheological grease composite strength is dominated by the continuous phase. With the increase in the magnetic field strength, the overall platform modulus of 1#MRG tended to remain unchanged, indicating that the magnetic chain has a limited influence on the composite strength of 1#MRG. Considering that the magnetorheological grease is subject to multiple influences such as temperature, magnetic field and continuous shear under actual working conditions, the evolution law of its rheological properties is analyzed in conjunction with the influence of temperature change on the platform modulus under a fixed magnetic field.

Figure 10 shows the variation curves of the platform modulus of each sample at different temperatures. At a fixed magnetic field of 55 mT, the platform modulus of 00#MRG showed a large increase with increasing temperature, indicating that the soap fiber structure in the magnetorheological grease appears to be untangled and broken and reorganized with increasing temperature [29], and the continuum phase cannot provide enough external force to bind the movement of magnetic particles. As a result, the large-scale magnetic chains formed under the action of magnetic fields can effectively enhance the composite structures. Under a low temperature field, the change in the platform modulus of 00#MRG was low, and when the experimental temperature reached 80 °C, 00#MRG showed a significant increase, indicating that the soap fiber structure was greatly damaged at 80 °C, a large number of magnetic particles could be released, and the magnetorheological grease composite strength was dominated by the discrete phase. Sample 1#MRG had a platform modulus change curve that flattens out over the entire experimental temperature range. It is shown that when considering the effect of a single temperature, the successive resistance to temperature change is also increased for higher consistency relative to temperature change.

It can be seen that the degree of soap fiber entanglement in the continuous phase is directly related to the external resistance during the movement of the magnetic chain, which has a more obvious effect on both the magnetic and rheological properties of magnetorheological grease. When the thermomagnetic coupling conditions are considered comprehensively, 00#MRG, which has a lower platform modulus, showed a large increase in apparent viscosity, a decrease in the thixotropic ring area, and a deterioration in shear stability after being subjected to external excitation by high temperature or a strong magnetic field. Sample 1#MRG, which has a higher platform modulus, did not show any obvious drastic change under external excitation during the entire experimental period and exhibited better shear stability.

Figure 10. Variation curves of platform modulus of each sample at different temperatures: (a) 00#MRG, (b) 0#MRG, (c) 1#MRG.

Figure 10. Variation curves of platform modulus of each sample at different temperatures: (a) 00#MRG, (b) 0#MRG, (c) 1#MRG.

4. Conclusions

Magnetorheological grease was prepared by using carbonyl iron powder as magnetic particles and lithium grease of different consistency grades as the continuous phase, and its rheological properties were observed using Anton Paar’s Physica MCR–301 (Berlin, Germany) rotational rheometer in the rotational and oscillatory shear modes. The results showed that:

(1)

Under the same temperature conditions, the apparent viscosity of the magnetorheological grease rose and the shear flow resistance increased as the magnetic field strength increased. The interaction between magnetic chains and the soap fiber structure had a structural enhancement effect on the magnetorheological grease composite system. On the other hand, 1#MRG showed insignificant changes in the rheological properties during the constant=temperature magnetization process, which was related to its higher degree of soap fiber entanglement, and the magnetic particles were still unable to sufficiently shear the soap fibers under the effect of a saturated magnetic field, which in turn agglomerated to form magnetic chains.

(2)

Under the same magnetic field conditions, as the temperature rose, the magnetorheological grease was affected by the temperature increase as the soap fiber structure underwent disentanglement, the strength of the continuous phase structure decreased, and the magnetic particles were released to form a columnar magnetic chain under the action of the magnetic field, which greatly enhanced the strength of the composite structure. Sample 1#MRG had good shear stability with fewer rheological property changes during temperature rising. While the continuous phase consistency of 00#MRG was lower, the degree of heat resistance was lower, the composite strength increased dramatically at 80 °C, the soap fiber structure suffered great damage due to high temperature, and the shear stability deteriorated.

(3)

Under thermomagnetic coupling conditions, magnetorheological grease was affected by a mixture of temperature increase and sustained shear. In the low temperature and low magnetic field condition, the magnetic particles were not able to break through the obstruction of the soap fiber structure to form large-scale magnetic chains under a low magnetic field, which had limited influence on the rheological properties. As the temperature rose to 80 °C, the magnetorheological grease with a lower degree of entanglement was damaged by the high temperature, and its rheological properties changed significantly with the fracture and reorganization of the soap fiber structure. However, with the increase in the the magnetic field strength, the magnetorheological grease with a higher degree of entanglement had a better temperature-increase resistance, and the higher consistency provided good containment of the magnetic chain aggregation, and the shear stability improved.