# Performance Analysis of Magnetorheological Porous Fabric Composite
## 3 Discussion  
### Viscosity Changeability  
Figure 4 shows the curve of viscosity variation with the shear rate of the test sample under zero-field conditions. As an important index to evaluate the performance of MRF, viscosity affects its output characteristics. It can be seen from Figure 4 that the apparent viscosity of different test samples decreases with the increase of shear rate, showing the phenomenon of shear thinning. The MRF at zero-field and zero shear rate behaves as a liquid state because it is not excited by the magnetic field, and its apparent viscosity is small, about 8.3 kPa-s. As the control group, the composite of untreated non-woven fabric and MRF showed an apparent enhanced viscosity compared with MRF under the zero-field and zero shear rate, and the initial viscosity of the 2 wt% sample group was about 34.2 kPa-s. The results show that the addition of non-woven fabric in the composite has a thickening effect, and the flow of suspended particles is hindered to a certain extent due to the three-dimensional mesh structure of the non-woven fabric and the lithium stearate attached to it. The peak viscosity of each test sample in the non-shearing state also indicates that each sample has high viscosity characteristics in the non-working state, which can ensure the sedimentation stability of the fluid material. With the increase in shear rate, particle clusters in the MRF composite samples were largely decomposed under the action of a high shear rate, resulting in a significant decrease in the viscosity of each sample. However, the downward trend is roughly the same, which also indicates that the addition of non-woven  
Figure 4: Variation of viscosity with shear rate under zero-field. fabric has no great influence on the controllable characteristics of MRF, which provides a certain basis for the subsequent application of this composite. As can be seen in Figure 4, the viscosity of the composite samples after pretreatment is generally larger than that without pretreatment. With the increase of a mass fraction of lithium stearate, the viscosity of the composite is also improved. Compared with the MRF sample, the viscosity of the other three groups of samples increased significantly due to the addition of non-woven fabric. The main reason is that the magnetic particle clusters without the MR effect are dispersed significantly and cannot form a chain-like structure. In this case, the viscosity is dominated by the non-woven fabric and lithium stearate. Figure 5 shows the viscosity curves of the five test samples under different magnetic flux densities. The increase of lithium stearate content cannot improve the viscosity of the composite with the increase of magnetic flux density. Moreover, the viscosity improvement rate of the composite even shows a downward trend. It can be seen from Figure 5 that when the magnetic flux density increases from 0.31 T to 0.6 T, the viscosity improvement rate of the composite obviously decreases. Further, the viscosity of some samples is even lower than that of MRF at 0.6 T. The main reason for this phenomenon was that the non-woven fabric was soaked in lithium stearate solution, and a certain amount of lithium stearate particles were adsorbed on the surface, which increased the internal viscosity of the composite, thus impeding the internal flow of the fluid and improving its viscosity. However, when the mass fraction of lithium stearate is too large, the mass fraction of magnetic particles in the composite will be relatively reduced. Moreover, the viscosity of the composite is dominated by the chain-like structure formed by the magnetic particles under the action of a strong magnetic field, which obstructs the movement of the fluid and thus exhibits certain viscosity characteristics.