A Comparative Analysis of Measured and Calculated Compressive Stresses of Magnetorheological Fluids under Unidirectional Compression and Constant Area

Abstract

Unidirectional compressive properties of magnetorheological (MR) fluids have been investigated under slow compression and constant area with different magnetic fields and different initial gap distances. Experimental tests of unidirectional compression were firstly carried out by using a commercial plate–plate rheometer. The theoretical model based on the continuous squeeze flow theory was developed to calculate the compressive stress. The comparisons between the measured and calculated compressive stresses of MR fluids were made. It showed that the compression resistance of the MR fluid in the magnetic field was much higher than that predicted by the theory. With the increasing magnetic flux density, the deviation between measured and calculated curves accelerated. Characteristics of the compressive stress variation with the reduction in gap distance have been analyzed. The structure strengthening effect induced by the chain structure aggregation in squeeze mode has been used to explain this deviation.

An experimental study on mechanical properties of a magnetorheological fluid under slow compression

“…In addition, the experimental values of compressive stress also show a clear inflection point about at ε =0.026 under B = 0.28 T, at ε =0.021 under B = 0.45 T at ε =0.016 under B = 0.63 T and at ε =0.012 under B = 0.81 T, respectively, as shown in Figure 4. The region from ε =0 to the inflection point is often called the elastic deformation region (Bi et al, 2022), where MR fluids withstand the load without breaking during compression. The region after the inflection point is often called the plastic flow region (Bi et al, 2022), where the structures of MR fluids go through the repeated formation/breakdown process.…”

“…Also, the normal force/compressive stress has been predicted to vary as F/N ∝ H X /(1- ε ) Y in the plastic flow region according to continuum media theories and the magnetic energy approaches, where the index X is around well in the range (1.5, 2) and the index Y is around well in the range (2, 2.5) (Bi et al, 2022; Vicente et al, 2011; Zhang et al, 2004). Ruiz-López et al have proposed a micromechanical model that predicts a power law scaling of the normal force with the magnetic field strength and the compressive strain squared F ∝ H 2 /(1- ε ) 2 .…”

“…A power law relationships between the compressive force/stress and 1− ε with exponent −2.5 have been predicted based on this theory, where ε is the compressive strain (Guo et al, 2013b; Ruiz-López et al, 2016). However, there is still an argument about whether the continuous media theory is suitable to deal with the slow compression because this theory is found to be not always valid to the low compressive strain and high particle concentration (Bi et al, 2022; Guo et al, 2013b; Ruiz-López et al, 2012). The deviations have been found in the curves of normal force versus compressive strain at low compressive strains (Ruiz-López et al, 2012, 2016).…”

“…Subsequently, it has been proved that the squeeze-strengthen effect improves the yield stress of MR fluids because of thick columns with solid ends (Zhang et al, 2004). A great deal of researches have been done on the compressive characteristics of MR fluids in squeeze mode (Bi et al, 2022;Liu et al, 2021;Mazlan et al, 2007Mazlan et al, , 2008Ruiz-Lo´pez et al, 2012;Vicente et al, 2011;Wang et al, 2021b). To predict the compressive resistance of MR fluids, several models have been proposed (Covey and Stanmore, 1981;Gartling and Phan-Thien, 1984;Guo et al, 2013b;Ruiz-Lo´pez et al, 2016).…”

“…And the compressive speed is often limited to a low constant value so that the particles of MR fluids can find a minimum energy configuration in a more or less static condition, which is the so-called slow compression (Vicente et al, 2011). The compressive speeds were found to present in the range of 1-680 mm/s for most of the literature ( Bi et al, 2022;Mazlan et al, 2007Mazlan et al, , 2008Ruiz-Lo´pez et al, 2012;Wang et al, 2021b).…”