Squeeze-strengthening of magnetorheological fluids (part 1): Effect of geometry and fluid composition

Abstract

Recent research has shown that magnetorheological fluid can undergo squeeze-strengthening when flow conditions promote filtration. While a Péclet number has been used to predict filtration in non-magnetic two-phase fluids submitted to slow compression, the approach has yet to be adapted to magnetorheological fluid behavior in order to predict the conditions leading to squeeze-strengthening behavior of magnetorheological fluid. In this article, a Péclet number is derived and adapted to the Bingham rheological model. This Péclet number is then compared to the experimental occurrence of squeeze-strengthening behavior obtained from several squeeze geometries and magnetorheological fluid compositions submitted to pure-squeeze conditions. Results show that the Péclet number well predicts the occurrence of squeeze-strengthening behavior in high-concentration magnetorheological fluid made from various particle sizes and using various squeeze geometries. Moreover, it is shown that squeeze-strengthening occurrence is increased when using annulus geometries or by increasing average particle radius. While lowering concentration increases filtration, tested conditions only led to squeeze-strengthening behavior after concentration had increased close to packing limit. Altogether, results suggest that the Péclet number derived in this study can be used to predict the occurrence of squeeze-strengthening for various magnetorheological fluids and squeeze geometries using the well-known rheological properties of magnetorheological fluids.

Magnetorheology: a review

“…201 Hegger and Maas 202 proposed a modeling approach that combined the rheological behavior with tribological effects to describe the squeezestrengthening effect. The squeeze-strengthening of MRFs was carefully investigated by Lucking-Bigué et al 203,204 They derived a Peclet number and adapted it to the Bingham rheological model. This Peclet number well predicted the occurrence of squeeze-strengthening in highly concentrated MRFs.…”

Squeeze-strengthening of magnetorheological fluids (part 2): Simultaneous squeeze–shear at high speeds

“…Using equation (8), the equivalent stress resulting from Figure 6(a) and (b) is plotted in Figure 8. These results now show that high compression speeds (1-5 mm/s) lead to constant equivalent stress (dashed line, 120 kPa), typical of a homogeneous (no squeezestrengthening) behavior (Bigue´et al, 2017). However, slow compression speeds (0.05-0.5 mm/s) lead to significant increase in the equivalent stress below the transition gap height ðhÞ (see green markers), such as expected from the squeeze-strengthening behavior.…”

“…As in this first part of this study, squeeze flows correspond to low plasticity numbers ðS\0:05Þ, which are dominated by yield stress, and thus, the compressive yield stress t 0 sq can be determined directly from the compressive force F (De Vicente et al, 2011; Meng and Filisko, 2005) where R eq = 24:4 mm is the equivalent radius of the annulus geometry. The equivalent radius is the radius that provides same compressive yield stress between annulus and disk geometries, as determined in the first part of this study (Bigue´et al, 2017).…”

“…To distinguish between advective and diffusive flow timescales, a Pe´clet number has been derived specifically for two-phase fluids exhibiting power-law rheological behavior (Collomb et al, 2004). In the first part of this work (Bigue´et al, 2017), this original Pe´clet number was adapted to MRF rheological behavior and presented in non-dimensional terms as the ratio of non-dimensional viscosity ðm Ã Þ to a modified Darcy number ðDa à ޅ”

“…MRF#1 contains 47% (by volume) of carbonyl iron particles (3-5 mm radius) dispersed in a low-viscosity silicone oil that exhibits Newtonian behavior. High-concentration MRF#1 was chosen to further the understanding provided in part 1 of this study, where it was used to demonstrate direct correlation between squeezestrengthening occurrence and the Pe´clet number in pure compression (Bigue´et al, 2017). A high-concentration MRF is also chosen for simplicity as low-concentration MRF submitted to filtration conditions was found to possibly require an increase in the concentration before squeeze-strengthening occurs (Bigue´et al, 2017).…”