Shear thickening prevents slip in magnetorheological fluids

Abstract

Magnetorheological (MR) fluids are smart fluids that solidify upon the application of a magnetic field by virtue of suspended magnetic particles forming chains. Here, the effect of shear thickening additives on the performance of MR fluids is explored and found to increase yield stress by 60% in fluids that have the same iron content. In order to explore the origin of this improvement, a series of flow-and oscillation-based rheology experiments were performed at various plate separations and the results were compared with a discrete dipole model of chain formation and breakage. Ultimately, conventional MR fluids, which are typically shear thinning, are found to yield at small strains that are consistent with slip failure where chains shear apart at one particle-particle joint. In contrast, shear thickening fluids reliably yield at high strain in a manner consistent with affine failure of the chain where each joint is pulled apart equally. The prevention of slip failure is attributed to the shear thickening additive locally increasing the effective viscosity as slip begins, thus preventing it from leading to yield. In addition to motivating the use of shear thickening agents broadly in MR fluids, these findings highlight the importance of additive choice in tuning rheological properties of MR fluids and the benefit of considering the microstructural and bulk behavior of the fluid simultaneously when synthesizing smart fluids.

Hardware Methods for Onboard Control of Fluidically Actuated Soft Robots

“…These properties can be tuned by varying the concentration of the active particles and changing the carrier fluid, balancing higher yield stress with increased density and viscosity (Wang et al, 2018). Various additives can also be added to improve the stability of the fluid and increase performance (Rendos et al, 2020a;Rendos et al, 2020b). Figure 3E depicts the working principle of a smart fluid as well as a soft robot controlled with an MR fluid.…”

Magnetorheological Fluid‐Based Flow Control for Soft Robots

“…In future work, the authors plan to exploit improvements to the composition of the MR fluid which can produce materials that achieve higher yield stresses at lower magnetic fields. [74] Experimental Section Soft actuators were molded layerwise. 1.6 mm-thick acrylic sheets were laser cut and assembled into molds using acrylic cement.…”

“…In future work, the authors plan to exploit improvements to the composition of the MR fluid which can produce materials that achieve higher yield stresses at lower magnetic fields. [ 74 ]…”

Reinforcing Magnetorheological Fluids with Highly Anisotropic 2D Materials

“…This ability to reversibly switch between a fluid‐like and solid‐like state has led them to be widely used in tunable dampers, valves, braking systems, and robotics [3–8] . One fascinating and fruitful avenue of MRF research has been the addition of particulate additives that, together with standard magnetic microparticles, add new functionality or improve MRF performance which is commonly quantified as a yield stress [9–12] . The majority of work has focused on isotropic nanoparticle additives, which have been shown to improve MRF stability and, if the particles are themselves magnetic, strengthen the MRF when solidified [13–15] .…”

“…[3][4][5][6][7][8] One fascinating and fruitful avenue of MRF research has been the addition of particulate additives that, together with standard magnetic microparticles, add new functionality or improve MRF performance which is commonly quantified as a yield stress. [9][10][11][12] The majority of work has focused on isotropic nanoparticle additives, which have been shown to improve MRF stability and, if the particles are themselves magnetic, strengthen the MRF when solidified. [13][14][15] These successes motivate the study of more specialized nanomaterials as additives, such as anisotropic nanomaterials, as anisotropy has been observed to tailor both magnetic and rheological properties.…”