Abstract
The increase of the yield stress versus the magnetic field is the most important quantity characterizing the efficiency of a magnetorheological suspension. The theory based on the formation of columnar aggregates predicts a linear variation with the volume fraction of magnetic particles. We shall review previous models for the calculation of forces and yield stress and will introduce a new one based on rupture at zero strain. The predictions of these models are compared with the experimental data obtained for carbonyl iron particles by different authors. Whereas previous analytical prediction strongly overestimates experimental yield stress, the one calculated from Finite Element Method (FEM) used with affine trajectories well reproduce the experiments and show a linear dependence with the volume fraction and a H3/2 behavior between 50 and 200kA/m. Nevertheless, at very high volume fractions (>55%) where the suspension can only flow in the presence of specific additives, the dependence of the yield stress versus the volume fraction and the magnetic field is dramatically changed. We observe a jamming transition which is triggered by the application of a low magnetic field and which depends strongly of the volume fraction. We will discuss the new perspectives arising by the use of these very high volume fractions.
Highlights
Magnetorheological (MR) suspensions are smart fluids made of magnetizable particles, with a typical size varying between 100 nm and a few microns dispersed in a carrier liquid, which can be mineral oil, silicone oil, ethylene glycol, etc
In order to obtain a high yield stress and a reversible magnetization, Magnetorheology and Jamming Transition very few materials are available, and in practice industrial MR fluids are based on carbonyl iron particles as they present a high saturation magnetization and are synthesized in large quantities to produce sintered magnetic circuits
We have found one paper (Lacis and Gosko, 2009) using an expression similar to Equation (1), with some tables derived from Finite Element Method (FEM) simulations for two particles and another based on FEM simulations between several particles in a single chain (Kang et al, 2012)
Summary
Magnetorheological (MR) suspensions are smart fluids made of magnetizable particles, with a typical size varying between 100 nm and a few microns dispersed in a carrier liquid, which can be mineral oil, silicone oil, ethylene glycol, etc. In the affine model, the predictions related to the 3 different approximations of forces: Equations (1, 3, 4),we recover the fact that the multipolar model gives a rather good prediction for low fields but, due to the linear magnetization hypothesis, highly overestimates the yield stress at high fields.
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