Stribeck Curve of Magnetorheological Fluid within Pin-on-Disc Configuration: An Experimental Investigation

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Magnetorheological (MR) fluids are suspensions of fine, low-coercivity, high-magnetizable particles in a continuous liquid phase. When subjected to magnetic field, the material exhibits a rapid change in the apparent viscosity of several orders of magnitude. This unique capability has been successfully exploited in automotive semi-active suspensions systems or systems for manufacturing high quality optics. In a majority of the existing systems the rheology of MR fluids is controlled by an external uniform field oriented perpendicularly to the fluid flow direction. In general, it is an inherent feature of MR systems operating in flow, shear or squeeze modes, respectively. There is an experimental evidence that the behavior of MR fluids in the so-called pinch-mode (in which the fluid is subjected to non-uniform magnetic field distributions ) clearly stands out against the remaining three operating modes. With the predecessors, the flow through the channel occurs once a pressure across it exceeds the field-dependent threshold pressure. For comparison, in pinch mode valves the magnetic flux energizes mostly the layers of the materials near the channel walls. The outcome is a change in the channel’s effective diameter achieved solely via material means without changing its geometry. To study the fluid’s unique behaviour in the mode the authors designed a prototype valve assembly and examined several fluid formulations of various particle concentration levels across a wide range of external (velocity, magnetic field density) stimuli in an organized effort to further comprehend the phenomenon. The obtained data indicate that the magnitude of the particular effect does not only depend on the magnitudes of the magnetic stimuli but also on the particle concentration. In general, the authors believe that the study may provide guidelines as to the selection of fluid formulations for developing novel valveless actuators utilizing MR fluids operating in pinch mode.

Section: Mr Pinch Valve Prototypementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Magnetorheological fluids subjected to non-uniform magnetic fields: experimental characterization

Kubík¹,

Gołdasz²,

Macháček³

et al. 2023

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“…The particles are spherical and average size (diameter) is 2.1 µm. The particle distribution is according Q3 [35]. The particle material is carbonyl iron.…”

Section: Test Samplementioning

confidence: 99%

Hydrodynamic response time of magnetorheological fluid in valve mode: model and experimental verification

Kubík¹,

Šebesta²,

Strecker³

et al. 2021

The transient behaviour of magnetorheological (MR) actuators affects their performance in progressive semiactive control suspension systems. The two sources of the time delay between the control signal and damping force are (a) dynamics of MR damper hardware and (b) the MR fluid dynamics. The significant part of the MR fluid response time is the so-called hydrodynamic response time which is connected with the transient flow. Due to the above, the main aim of this paper is to experimentally determine the hydrodynamic response time of MR fluid and present systematic means for characterizing it via computational fluid dynamics (CFD) or analytical tools. The unique measurement method using an in-house patented slit flow rheometer is presented. The essence of the method relies on determining the pressure drop variation with the time spent by the fluid in the MR gap. The experimental determined hydrodynamic response time of MR fluid ranges from 0.4 to 1 ms for a selected gap size and a range of magnetic field stimuli. The results show that the higher the magnetic field, the lower the hydrodynamic response time is. Both CFD and analytical models exhibit similar trends as the experimental data. Moreover, the impact of temperature and gap size was determined. Here, the higher the gap size and temperature of MR fluid, the longer the response time is.

“…All the experiments were performed at room temperature (25 • C). Some studies have tested the Stribeck curves of some commercial MRFs, and found that MRF is mainly in the boundary lubrication state [45]. Therefore, the lubrication performance of base oil was also studied based on Stribeck curve…”

Section: Friction Experimentsmentioning

confidence: 99%

Effect of base oil lubrication properties on magnetorheological fluids

Zhang

Jiang

Ouyang

et al. 2021

The effects of the lubricating properties of the base oil on the rheological properties of magnetorheological fluid (MRF) are studied. The results from three base oils with different lubricating performances show that an MRF with poor boundary lubricity has a higher yield stress and is more likely to exhibit shear thickening. The shear stresses and normal force in the MRF and the shear-thickening phenomenon mainly affect by the friction state between the ferromagnetic particles and the plates. The evolution mechanism of the MRF particle structure explain from the perspective of tribology using a normalization method based on the friction coefficient and the Stribeck curve.