Study of magnetorheological fluids at high shear rates (original) (raw)

Rheometry on magnetorheological (MR) fluids

Rheologica Acta, 1996

Test fixtures of a commercial concentric cylinder rheometer (Physica Rheolab MC 20) were modified to enable measurements under magnetic inductions up to 0.5 Tesla in a shear rate range of 0.1 up to 1000 s-1 and temperatures 0 ° to 150°C. In the 2x90°-cups only two 90 ° sectors of the stationary part of the double concentric cylinder arrangement are submitted to the magnetic field which is created outside the test tools by an electromagnet. A prototype of a 360~-cup contains the electromagnet within the cup and avoids the correction necessary for the sector geometry. Measurements are shown for a carbonyl iron MR fluid and two nano MR fluids. An encouraging comparison of the viscosity function and MR effect (shear stress changes due to the field) measured by using the various cups is presented. The detailed investigation of the magnetic field distribution in the tools yields a distinct radial field gradient and also stray fields that make the quantification of the effective field in the gap difficult. The change of the field when the gap is filled with MR fluid is addressed. MR effects up to 13000 Pa have been found, the limited torque range of the rheometer making it necessary to use relatively small gap dimensions which introduce errors due to edge effects. Shear rates up to 40000 s-1 as typical for the application in dampers were investigated by a piston-driven capillary rheometer making use of a thermostated rectangular slit with superimposed magnetic field. A satisfactory agreement of the magnetorheological data with the concentric cylinder results is found in the overlapping shear rate range.

Magnetorheological fluids: a review

Soft Matter, 2011

Magnetorheological (MR) materials are a kind of smart materials whose mechanical properties can be altered in a controlled fashion by an external magnetic field. They traditionally include fluids, elastomers and foams. In this review paper we revisit the most outstanding advances on the rheological performance of MR fluids. Special emphasis is paid to the understanding of their yielding, flow and viscoelastic behaviour under shearing flows.

Viscoelastic properties of magnetorheological fluids

Rheologica Acta, 2004

We have studied the rheological properties of some magnetorheological fluids (MRF). MRF are known to exhibit original rheological properties when an external magnetic field is applied, useful in many applications such as clutches, damping devices, pumps, antiseismic protections, etc. While exploiting parameters such as magnetic field intensity, particle concentration and the viscosity of the suspending fluid, we highlighted the importance of each one of these parameters on rheology in the presence of a magnetic field. We made this study by conducting rheological experiments in dynamic mode at very low strain which facilitates the comprehension of the influence of the structure on MRF rheology. Our results confirmed the link between the magnetic forces which ensure the cohesion of the particles in aggregates, and the elastic modulus. Moreover, we found that the loss modulus varies with the frequency in a similar manner than the elastic modulus. The system, even with the smallest deformations, was thus not purely elastic but dissipates also much energy. Moreover, we demonstrated that this dissipation of energy was not due to the matrix viscosity. Actually, we attributed viscous losses to particle movements within aggregates.

Properties and applications of Magnetorheological fluids

This brief introduction describes the mechanical, rheological and magnetic properties of the magnetorheological (MR) fluids for feasible engineering applications. The typical modes of exploiting this technology are shown and discussed. An increasing number of industrial applications illustrate how the MR fluids peculiar properties may be used to provide optimal performance in semi active damping and dissipative devices.

Dynamic rheology of sphere-and rod-based magnetorheological fluids

The Journal of chemical …, 2009

The effect of particle shape in the small amplitude oscillatory shear behavior of magnetorheological ͑MR͒ fluids is investigated from zero magnetic field strengths up to 800 kA/m. Two types of MR fluids are studied: the first system is prepared with spherical particles and a second system is prepared with rodlike particles. Both types of particles are fabricated following practically the same precipitation technique and have the same intrinsic magnetic and crystallographic properties. Furthermore, the distribution of sphere diameters is very similar to that of rod thicknesses. Rod-based MR fluids show an enhanced MR performance under oscillatory shear in the viscoelastic linear regime. A lower magnetic field strength is needed for the structuration of the colloid and, once saturation is fully achieved, a larger storage modulus is observed. Existing sphere-and rod-based models usually underestimate experimental results regarding the magnetic field strength and particle volume fraction dependences of both storage modulus and yield stress. A simple model is proposed here to explain the behavior of microrod-based MR fluids at low, medium and saturating magnetic fields in the viscoelastic linear regime in terms of magnetic interaction forces between particles. These results are further completed with rheomicroscopic and dynamic yield stress observations.

Fabrication and Characterisation of Magnetorheological Shear Thickening Fluids

Frontiers in Materials, 2020

In this article, a magnetorheological shear thickening fluid (MRSTF) was fabricated based on magnetorheological (MR) material and shear thickening fluid (STF). The STF was firstly fabricated as the liquid phase, and carbonyl iron particles were then mixed with the prefabricated STF to synthesise a series of MRSTFs with various iron concentrations. Then, a rheometer was used to measure their viscosities by varying the shear rate under various magnetic fields. Both static and dynamic tests were conducted to study the rheology of MRSTFs under different magnetic fields. The tested results revealed that the MRSTF showed shear thickening under zero magnetic field and MR effect with increasing applied magnetic field. It was also noted that the viscosity of the MRSTFs can be controlled by both shear rate and the applied magnetic field. The concentration of iron particles played an important role in the MRSTFs’ rheological properties. The MRSTFs with higher iron particle concentrations revea...

A Study on Properties and Selection Criteria for Magneto- Rheological (MR) Fluid Components

2014

Magneto rheological (MR) fluid technology has been proven for many industrial applications like shock absorbers, actuators, seat dampers, etc. However, MR fluids can only exhibit a yield stress of 50-100 kPa at a magnetic field of 150-280 kA/m. Hence, the proper selection of various MR fluid components like carrier fluid, magnetic particles and additives to satisfy the high yield stress applications remained a challenge. Basically, MR fluid is the colloidal suspension of micron sized, polarizable magnetic particles in the magnetically neutral carrier fluid whose viscosity can be varied from liquid to semisolid with the help of magnetic field. This paper presents basic properties of the MR fluids and their developments during recent years. This paper discusses the possible candidates of carrier fluid like mineral oil, synthetic oil, silicone oil, etc.; magnetic particles like electrolytic iron particles, carbonyl iron particles, iron/cobalt alloys, etc.; various additives and surfact...

An improved properties of bidispersed magneto-rheological fluids

RSC Adv., 2014

We have investigated the influence of nanosized particle concentration on rheological properties when mixed with a magnetorheological (MR) fluid. We have also studied the structural, morphological and magnetic properties of ferrofluid-based MR fluids (F-MRFs). Field-induced rheological and viscoelastic properties of F-MRFs with varying shear rate and strain amplitude have been investigated. The Herschel-Bulkley model was found to fit well with the flow behaviour of F-MRFs. In the oscillatory strain sweep test, F-MRFs show linear viscoelasticity at low strain and the storage modulus (G 0) is higher than the viscous modulus (G 00), which indicates the existence of strong links among the particles that form the microscopic structures. The storage modulus increases with increasing weight fraction of nanosized particles. Furthermore, the loss factor (ratio of G 00 and G 0) was also investigated as a function of magnetic field strength. In addition, time-dependent relaxation behaviour of magnetically induced chain-like structures has also been described. The study reveals that the addition of nanoparticles to MR fluids increases the viscosity as well as the fluid stability under a magnetic field.

A Study of Properties, Preparation and Testing of Magneto-Rheological (MR) Fluid

Magneto rheological (MR) fluids have been investigated to be of much importance due to their magneto rheological dependant properties. Magneto Rheological is a branch of rheology that deals with the flow and deformation of the materials under an applied magnetic field. These types of materials change their rheological properties under the application of magnetic field applied and turn from liquid to solid in just few seconds. MR fluid is the colloidal suspension of micron sized, polarizable magnetic particles (iron metal particle) in the magnetically neutral carrier fluid (low viscosity paraffin oil / silicon oil) whose viscosity can be varied from liquid to semisolid with the help of magnetic field. Magneto rheological (MR) fluid technology has been proven for many industrial applications like shock absorbers, actuators, seat dampers, etc. This paper presents basic properties, preparation, testing and implementation of MR fluid in conventional damper.

Transient rheology of a magnetorheological fluid under shearing

2011

Transient behaviour of a magnetorheological (MR) fluid under constant long lasting shearing is studied using Anton Paar MCR 301 rheometer and MRD180/1T magneto-cell. Effect of the shear rate, magnetic flux density and surface material and texture of the plate-plate measuring geometry are investigated by a series of time sweep measurements. In addition to the original titanium Anton Paar rotor two custom made aluminum rotors with different plate surface textures are used. It is found that the shear stress of MR fluid typically has either a steadily decreasing or increasing trend as a function of time depending about measuring parameters, mostly shear rate. The results also show that the rotor plate texture and material can have a significant effect to the measurement.