Shear rheology of magnetorheological fluids under triaxial fields*

Magnetorheological (MR) fluids are suspensions of magnetizable microparticles in a Newtonian fluid. In an external magnetic field, these particles polarize and the resulting forces cause structure to form on short time scales. The microstructure translates to a sharp change in the rheological properties of the sample. In particular, the MR fluids show a pronounced shear-thinning behavior.

Traditionally, MR is studied under steady uniaxial DC fields. In this scenario, the microstructure consists of (1D) chain-like aggregates aligned with the field. However, it has been shown that more complex structures, e.g. 3D networks of sheets, can be generated by simply applying AC triaxial fields of high frequency [1].

In this work, the rheological response of MR fluids under shear flow and triaxial fields is evaluated through particle level simulations. Several field configurations and shear rates are tested to ascertain the interplay among them, focusing on their effect on the microstructure and viscosity. Finally, we seek to collapse those results in terms of the Mason number (ratio between disrupting shear and magnetic attractive forces).

References

[1] Martin et al. (2004). Physical Review E, 69(2), 021508