Magnetorheological Fluids

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.

Most current seatbelt load limiter technologies could only offer three or fewer predetermined patterns of seatbelt restraint force. However, researches have shown that, to better realize adaptive protection to different occupants under different crash severities, a continuously and real-time adjustable load limiter may be one step further. This concept could be especially favorable to vulnerable occupants such as small stature females and elderly people. Ideas have emerged suggesting possibility of using magnetorheological fluid (MRF) to realize such load limiter (MR-LL). This paper presents a concept study of MR-LL, aiming at evaluating its feasibility and establishing basic guidelines for prototype development. Configuration of an MR damper integrated with seatbelt retractor is selected in the study, in which the seatbelt force can be controlled by varying the strength of magnetic field exerted on the MRF inside the damper. The MR damper is numerically modeled and validated against experimental data found in the literature. Then by merging the MR damper model with a simplified occupant and seatbelt model subjected to sled impact loading, the performance of MR-LL under different parameter settings is studied and optimized. The simulation results demonstrate proof of the concept, indicating that the proposed MR-LL can generate various seatbelt force patterns with a wide adjusting range, thus to meet the requirement of both occupant adaptability and crash severity adaptability. Possible limitations of the proposed MR-LL are also discussed.

The steady-state magneto-mechanical response of a magnetorheological fluid (MRF), prepared by dispersing 40 wt % of magnetically soft, lightweight coral-network-shaped yttrium iron garnet (YIG; Y 3 Fe 5 O 12) powder in silicone oil (140 cSt) is studied as a function of shear rate, under different applied magnetic fields (B). The results show that the yield strength (τ Y) and viscosity (η) of the MRF increase with B, and are strongly influenced by the physical parameters of the particles such as morphology and saturation magnetization. The low density of the YIG-particles, leading to higher volume fraction for equal mass loading, results in a higher viscosity in the absence of a magnetic field, in comparison to that of conventional metallic Fe-particle-based MRFs. Due to this, there is a relatively smaller increase in τ Y and η when the magnetic field is switched on. The YIG-particles-based MRF has the advantages of high chemical stability, thermo-oxidative resistance and low-cost.

This paper presents a novel design
of multi-disks Magnetorheological braking
system (MR brake) for automotive application.
Magnetic saturation in both electromagnetic
core and MR fluid is considered in this
paper. The electromagnetic analysis of the
proposed configuration is carried out using
Finite Element based COMSOL multiphysics
software (AC/DC module). The system geometry,
created using AutoCAD software, is
discretized using a finite number of triangular
elements with a higher concentration of
elements near the internal boundaries. Post
processing option of COMSOL multiphysics
software is utilized to calculate the magnetic
field distribution and magnetic flux density
inside the MR fluid and electromagnetic core.
A one dimensional analytical model is developed
to calculate the braking torque of
the proposed system. The performance of
the proposed design shows improvement over
the designs available in the existing literature
considering the same dimensional restrictions.

The mitigation of seismic-induced vibrations is essential for the effective protection of buildings and occupants during earthquakes. This especially applies to slender buildings with metallic frames; in this case, the structure’s geometrical layout and relatively low damping properties favor an excessive and potentially catastrophic oscillatory response to a seismic event. Semiactive systems for energy dissipation are among the most commonly used strategies to control this oscillatory response. They offer the right balance between the reliability of passive devices and the versatility and adaptability of fully active systems. In this work, a vibration-suppression system based on dissipative bracings that integrate commercial magnetorheological fluid dampers (MRDs) was designed and validated through experimental tests on a true-scale structural model that was representative of a five-story slender building with a metallic frame. A practical and robust approach was proposed for: (1) The definition of the MRD type in compliance with a predefined mitigation target for seismic-induced accelerations on each floor of the structure; (2) The modeling of the MRDs, contribute to the dynamic response of the structural system. The approach involves a linearized formulation of the characteristic damping curves of the MRDs at different values of the activating current. By relying upon this linearization, a rapidly converging iterative process was set up to simulate the seismic response of the structure in the case of activated or deactivated dampers. The reference structure and the vibration-suppression system were then manufactured and tested on a sliding table, which provided realistic seismic excitation. The good correlation levels between the numerical predictions and the experimental measurements proved the effectiveness of the conceived system and of the approaches that were used for its design and simulation.

We report a systematic experimental investigation on the use of nanofibers to enhance the magnetorheological (MR) effect in conventional (microsphere-based) MR fluids formulated in polyalphaolefin oil/1-octanol. Two kinds of nanofibers are employed that have very similar morphology but very different magnetic properties. On the one hand we use non-magnetic goethite nanofibers. On the other hand we employ magnetic chromium dioxide nanofibers. For appropriate concentrations the on-state relative yield stress increases up to 80% when incorporating the nanofibers in the formulation. A similar yield stress enhancement is found for both nanofibers investigated (magnetic and non-magnetic) suggesting that the main factor behind this MR enhancement is the particle shape anisotropy. The relative yield stresses obtained by partial substitution of carbonyl iron particles with nanofibers are significantly larger than those measured in previous works on MR fluids formulated by partial substitution with non-magnetic micronsized spherical particles. We also demonstrate that these dimorphic MR fluids also exhibit remarkably larger long-term sedimentation stability while keeping the same penetration and redispersibility characteristics.

A non-affine visco-elasto-plastic constitutive equation with yield stress is proposed to simulate the response of magnetorheological fluids to driving forces. The equation yields realistic flow patterns in the pressure gradient driven fully developed tube flow which combine the effects of viscoelasticity and yield stress. The interplay of yield stress and viscoelasticity results in longitudinal velocity profiles, which can be controlled by adjusting the strength of the applied magnetic field. However, for physically realistic velocity profiles to exist the material parameters of the fluid and the steady pressure gradient must satisfy certain restrictions.

In this paper a method is studied to analyze the recovering of optimal damping constant because of temperature increasing in a shock absorber. The increasing on temperature leads to decreasing that constant by mean dynamic viscosity such to modify the dynamic behavior of a 2DOF system built-up by sprung and unsprung mass.
A MagnetoRheological damper was designed according with the desired optimal damping constant once fixed temperature design. It was seen that the increasing of temperature this constant is lost. As MagnetoRheological-Fluids allows us to increase the viscosity, we use a control signal by a state feedback of reduced order to create a such magnetic induction field to recover the optimal damping constant at higher temperature than design on

Magnetorheological fluid (MRF) is a smart material whose rheological properties can be varied by a magnetic field; it has been applied in the development of semiactive dampers for a variety of applications. The material essentially consists of a suspension of magnetic particles in a nonmagnetic carrier fluid. It is important to understand the magnetic response of MRF and its dependence on several parameters for improving and designing MRF devices. The purpose of this work is to develop a constitutive model that describes the behavior of the shear yield stress of the material as function of the magnetic field and composition. Taking into account that the material changes its rheology and apparent viscosity according to magnetic field, a magnetically induced state transition is proposed; by the use of a state transition equation, a constitutive model for shear yield stress is defined, consisting of an expression that relates composition of the material and the stimulus applied, it also associates the volume fraction of particles, magnetic field and the material that composes the particles.

This study investigates the automotive magnetorheological (MR) shock absorber behaviour in conditions of changing temperature. Its temperature-dependent behaviour was quantified between ambient and maximal operating temperatures of the device. Aspects addressed include the temperature dependence of the control coil resistance in the absorber, the influence of operating current level on control coil temperature and the temperature dependence of the absorber force response and energy dissipation in the system. The results of experiments enabled us to evaluate the mechanical performance of the absorber at varied temperatures.

The braking system is among the most significant active safety systems in a vehicle application for preventing injuries and property damage. Whether for light or heavy vehicles, brakes are no longer a small issue whereas it becomes a crucial problem to maintain the safety and to avoid the unpredictable cases especially on the road. Advanced technology in automotive industry has produced a new coming design of Magnetorheological (MR) brake which a field change is triggered off by changing the current in the coils exciting the magnetic field. MR fluid is one of the members of smart material which applicable usage to achieve the standard of rotary high speed similar as the existing brake disc in hydraulic system. A new MR brake disc was proposed using the squeeze mode rather than only conventional mode at the upper and lower rotating rotor. Parameters that have been considered are the types of MR fluid, selection of magnetic material, non-magnetic material and coil configurations. Then...

Vibration has been a major constraint in the machining industries as it has catastrophic effects on the machining parameter. Though there have been several attempts made by the researchers each had their own limitations and constraints. In metal cutting, Magnetorheological fluid (MRF) has proved to be effective in vibration suppression when employed as a semi-active damper. MRF is a smart non-Newtonian fluid which has the capacity to alter its viscosity instantaneously on the application of magnetic field. Along with this property and its robust nature they have used in a wide variety of places as a damper. One major limitation is its settling of magnetic particles which are suspended in a non-magnetic fluid. The settling rate will be further aggravated when the current supplied to coil is increased. Increased current will increase the heat produced in the coil which in turn will heat the non-magnetic fluid wherein its viscosity gets reduced. This problem of settling of iron particles can be prevented by adding stabilizers, similarly the size of particles also has an immediate effect on settling. In the current investigation Titanium and Activated carbon was added as stabilizers to magnetorheological fluid and then the viscosity change brought about in the fluid was studied. Further to support and add clarity to the work variable cutting speed and feed test was also performed. From the experimental results it was evident that stabilizers (activated carbon by 0.1% of weight) in MRF has increased the viscosity and thereby aided in an effective turning process of hardened SS410 steel.

Magneto Rheological Elastomer (MRE) have been the topic of extreme study throughout the previous hardly any decades. They show novel properties or are possible materials for the new-age devices. These elastomers are new engineering materials remembered for the class of dynamic objects its mechanical property can be limited by an exterior magnetic field [3]. They can be used in transduction and the other way around. These two significant properties of magneto rheological (MR) elastomer provide ascend to numerous possible purposes as actuators, transducer, automobile deferment systems, clutches, brakes, vibration isolators, and constraints. This is comparable to the conduct of  as MR liquid system or an electro rheological (ER) system.

ABSTRACT A magnetorheological (MR) damper is a promising appliance for semi-active suspension systems, due to its capability of damping undesired movement using an adequate control strategy. This research has been carried out a phenomenological dynamic model of two MR dampers using an adaptive-network-based fuzzy inference system (ANFIS) approach. Two kinds of Lord Corporation MR damper (a long stroke damper and a short stroke damper) were used in experiments, and then modeled using the experimental results. In addition, an investigation of the influence of the membership function selection on predicting the behavior of the MR damper and obtaining a mathematical model was conducted to realize the relationship between input current, displacement, and velocity as the inputs and force as output. The results demonstrate that the proposed models for both short stroke and long stroke MR dampers have successfully predicted the behavior of the MR damper with adequate accuracy, and an equation is presented to precisely describe the behavior of each MR damper.

ABSTRACT Magnetorheological (MR) fluid is a suspension of small iron particles, where, in the presence of a magnetic field, the solid particles arranged themselves as deformable chains. The deformation of the chain structure can be performed in three common modes known as flow mode, shear mode and squeeze mode. Among the three, the flow and shear modes have been widely investigated and used in commercial applications. Nevertheless, limited focus has been given to the combination of both modes. Furthermore, the existing combination between the flow and shear mode has been always defined at the same effective area, which is commonly known as the shear-flow mode. This paper provides a new perspective of mixed mode by arranging in series the different modes in the same MR cell. In order to manifest the theoretical model, an effective area representing the shear-flow mode is positioned separately with another effective area of the pure flow mode. The magnetic circuit design is validated by using the finite element method in 2D simulation. Moreover, the simulated results of magnetic flux density in the MR fluid are used to predict the force produced by the flow and shear-flow modes. The fabricated cell is tested under quasi-static loading and the results are compared with those that were predicted. It can be concluded that, to a certain extent, the obtained experimental results have been successfully predicted by the proposed model.

Magnetorheological (MR) fluid is a suspension of small iron particles, where, in the presence of a magnetic field, the solid particles arranged themselves as deformable chains. The deformation of the chain structure can be performed in three common modes known as flow mode, shear mode and squeeze mode. Among the three, the flow and shear modes have been widely investigated and used in commercial applications. Nevertheless, limited focus has been given to the combination of both modes. Furthermore, the existing combination between the flow and shear mode has been always defined at the same effective area, which is commonly known as the shear-flow mode. This paper provides a new perspective of mixed mode by arranging in series the different modes in the same MR cell. In order to manifest the theoretical model, an effective area representing the shear-flow mode is positioned separately with another effective area of the pure flow mode. The magnetic circuit design is validated by using ...

ABSTRACT: The fluid dynamics of dampers is investigated for the case where the damping fluid flows through passages in which a magnetic field is applied. This is a specific case of a new and promising field of applications that has emerged through the design of devices that take advantage of some properties of the so-called electrorheological fluids and magnetorheological fluids (ERF and MRF). These fluids are created when a base fluid is seed with very small dielectric or iron particles, so that it reacts to electric or magnetic fields by developing some non-Newtonian characteristics, most prominently a yield stress, viscosity change, and also viscoelasticity. These fluid properties can be controlled through control of the electric or magnetic fields’ strength. In this paper, a typical damping load is modeled and related to the required flow of a MRF inside the damper. To this end the fluid is modeled as a Bingham fluid with time-varying yield-stress. The analysis here developed makes it possible to determine the magnetic field variation necessary in order to achieve a specific displacement of the damper’s piston. The flow equations are analytically solved for any time-history of the dimensionless fluid’s yield-stress. Main results are some simplified relationships that correlate damping load and magnetic field time-variations. These results aim at providing analytical tools that may facilitate dampers’ design.

The dynamics of field-induced structures in very dilute dipolar colloidal suspensions subject to rotating magnetic fields have been experimentally studied using video microscopy. When a rotating field is imposed the chain-like aggregates rotate with the magnetic field frequency. We found that the size of the induced structures at small rotational frequencies is larger than at zero rotating frequency, i.e. when an uniaxial magnetic field is applied. At higher frequencies, the average size of the aggregates decreases with frequency following a power law with exponent −0.5 as the hydrodynamic friction forces overcome the dipolar magnetic forces, causing the chains break up. A non-thermal molecular dynamics simulations are also reported, showing good agreement with the experiments.