magneto rheological fluid MD TARIQUE JILANI

MAGNETO RHEOLOGICAL FLUIDS

Dept. of Mechanical Engineering, AITM-Bhatkal Page 1

ANJUMAN INSTITUTE OF TECHNOLOGY AND

MANAGEMENT

(AFFLIATED TO VISVESVARAYA TECHNOLOGICAL UNIVERSITY, BELGAUM

RECOGNISED BY AICTE, NEW DELHI)

A SEMINAR REPORT ON

“MAGNETO RHEOLOGICAL FLUID”

Presented by

MD TARIQUE JILANI :+919986704192 : [email protected]

mailto:[email protected]



ABSTRACT

Magneto rheological fluids commonly known as MR fluids sometimes referred to as Ferro

fluids are suspensions of solid in liquid whose properties changes drastically when exposed

to magnetic field. Magneto rheological (MR) fluids are materials that respond to an applied

field with a dramatic change in their rheological behavior. The essential characteristic of

these fluids is their ability to reversibly change from a free-flowing, linear, viscous liquid

to a semi-solid with controllable yield strength in milliseconds when exposed to a magnetic

field. MR fluids find a variety of applications in almost all the vibration control systems. It

is now widely used in automobile suspensions, seat suspensions, clutches, robotics, design

of buildings and bridges, home appliances like washing machines etc. The key to success

in all of these implementations is the ability of MR fluid to rapidly change its rheological

properties upon exposure to an applied magnetic field. Magneto rheological (MR) fluids

offer solutions to many engineering challenges. The success of MR fluid is apparent in

many disciplines, ranging from the automotive and civil engineering communities to the

biomedical engineering community. This well documented success of MR fluids continues

to motivate current and future applications of MR fluid.



Chapter 1

INTRODUCTION

A Magneto Rheological fluid (MR fluid) is a type of smart fluid in a carrier fluid, usually

a type of oil. When subjected to a magnetic field, the fluid greatly increases its apparent

viscosity, to the point of becoming a viscoelastic solid. Importantly, the yield stress of the

fluid when in its active (“on”) state can be controlled very accurately by varying the

magnetic field intensity. It is this property which makes it desirable to use in different

vibration controlling systems. The upshot is that the fluid’s ability to transmit force can be

controlled with an electromagnet, which gives rise to its many possible control-based

applications. MR fluid is different from a Ferro fluid which has smaller particles. MR fluid

particles are primarily on the micrometer-scale and are too dense for Brownian motion to

keep them suspended (in the lower density carrier fluid). Ferro fluid particles are primarily

nanoparticles that are suspended by Brownian motion and generally will not settle under

normal conditions. As a result, these two fluids have very different applications. Magneto

rheological fluid (MRF) is a smart fluid whose properties can be controlled with the help

of metal particles and magnetic field. These fluids have the ability to transmit force in a

controlled manner with the help of Magnetic field, thus improving their performance

especially in areas where controlled fluid motion is required. Some applications of

Magneto rheological fluid technology are in dampers, brakes, journal bearings, pneumatic

artificial muscles, optics finishing, fluid clutches, aerospace etc. where we give electrical

inputs and get the mechanical output comparatively faster and in a controlled manner.



Chapter 2.

RECENT ADVANCES

Recent studies which explore the effect of varying the aspect ratio of the ferromagnetic

particles have shown several improvements over conventional MR fluids. Nano wire based

fluids show no sedimentation after qualitative observation over a period of three months.

This observation has been attributed to a lower close-packing density due to decreased

symmetry of the wires compared to spheres, as well as the structurally supportive nature

of a Nano wire lattice held together by remnant magnetization. Further, they show a

different range of loading of particles (typically measured in either volume or weight

fraction) than conventional sphere- or ellipsoid-based fluids. Conventional commercial

fluids exhibit a typical loading of 30 to 90 wt. %, while Nano wire-based fluids show a

percolation threshold of ~0.5 wt. % (depending on the aspect ratio).They also show a

maximum loading of ~35 wt. %, since high aspect ratio particles exhibit a larger per particle

excluded volume as well as inter-particle tangling as they attempt to rotate end-over-end,

resulting in a limit imposed by high off-state apparent viscosity of the fluids. This new

range of loadings suggests a new set of applications are possible which may have not been

possible with conventional sphere-based fluids.

Newer studies have focused on dimorphic magneto rheological fluids, which are

conventional sphere-based fluids in which a fraction of the spheres, typically 2 to 8 wt. %,

are replaced with Nano wire. These fluids exhibit a much lower sedimentation rate than

conventional fluids, yet exhibit a similar range of loading as conventional commercial

fluids, making them also useful in existing high-force applications such as damping.

Another way to increase the performance of magneto rheological fluids is to apply a

pressure to them. In particular the properties in term of yield strength can be increased up

to ten times in shear mode and up five times in flow mode.



Chapter 3.

WHAT ARE MR FLUIDS?

MRFT stands for Magneto-rheological fluid technology. The essential components of

MRFT are MR fluid and a magnetic field to control the viscous property of the fluid. The

basic principle of MRFT is that very small suspended particles having magnetizing

properties are introduced in the base fluid. When a magnetic fluid is applied to this fluid,

these particles form a chain aligned in the direction of the field which creates a resistance

to the fluid flow. Resulting, an increase in the fluid viscosity takes place. Thus in the

presence of magnetic field the MR fluid converts into a semi solid with an increase in its

yield strength. This work phenomenon takes only milliseconds to occur. MR fluids thus

act similar to Bingham fluids used in many engineering applications. In the absence of

magnetic field, the MR fluid behaves like Newtonian fluids.

Another Definition of MR Fluid given by:

Dr. H. Hirani Mechanical Engnieering Department, IIT Delhi

RHEOS (Greek Word) = to FLOW (English Word)

RheoLOGY=Science of Material flow under external load condition.

MAGNETOrheological FLUID= Fluid whose apparent viscosity increases with the

application of Magnetic Field.



3.1 Components/Ingredients

Magneto rheological (MR) fluids are basically non colloidal suspensions of micro sized

magnetisable particles in an inert base fluid along with some additives. Thus there are

basically three components in an MR fluid:

A. Base fluid,

B. Metal particles and

C. Stabilizing additives.

A. Base fluid

The base fluid is an inert or non-magnetic carrier fluid in which the metal particles are

suspended. The base fluid should have natural lubrication and damping features. For better

implementation of MRF technology the base fluid should have a low viscosity and it should

not vary with temperature. This is necessary so that MRF effect i.e. variation of viscosity

due to magnetic field becomes dominant as compared to the natural viscosity variation.

Due to the presence of suspended particles base fluid becomes thicker. Commonly used

base fluids are Hydrocarbon oils, mineral oils and Silicon oils.

B. Metal particles

For proper utilization of this technology we need such type of particles which can

magnetized easily and quickly therefore we use metal particles. Metal particles used in the

MR-technology are very small. Size of the particle is approximate of the order of 1μm to

7μm. Commonly used metal particles are carbonyl iron, powder iron and iron cobalt alloys.

Metal particles of these materials have the property to achieve high magnetic saturation

due to which they are able to form a strong magnetizing chain. The concentration of

magnetic particles in base fluid can go up to 50%. (approx.)



C. Additives

It is necessary to add certain additives to MR fluid for controlling its properties. These

additives include stabilizers and surfactants. Surfactants serve to decrease the rate of

settling of the metal particles. While the functions of additives are to control the viscosity

of the fluid, maintain friction between the metal particles and to reduce the rate of

thickening of the fluid due to long term use of the fluid thus additives also increase the life

of the MR fluid. Commonly used additives are ferrous oleate and lithium stearate. All the

three components of an MR fluid define its magneto rheological behavior. Changing any

one component will result in change in the Rheological and Magneto rheological properties

of the MR fluid. An optimum combination of all the three components is necessary to

achieve the desirable properties of an MR fluid.



3.2 Modes of Operation.

An MR fluid is used in one of three main modes of operation, these being

a) Flow mode,

b) Shear mode and

c) Squeeze flow Mode.

3.2.1 Flow mode.

These modes involve, respectively, fluid flowing as a result of pressure gradient between

two stationary plates as shown in Fig.

Fig 3.2.1 Flow mode

The magnetic field is perpendicular to the planes of the plates, so as to restrict fluid in the

direction parallel to the plates.



3.2.2 Shear mode.

These modes involve, respectively, fluid flowing between two plates moving relative to one

another.

Fig 3.2.2 Shear Mode

3.2.3 Squeeze-flow mode.

These modes involve, respectively, fluid flowing between two plates moving in the

direction perpendicular to their planes.

Fig 3.2.3 Squeeze-flow mode



3.3 Working Principle of MR Fluid Technology

The MR fluid is a smart fluid whose properties can be controlled in the presence of

magnetic field. In the absence of magnetic field, the rheological properties of the MR fluid

are similar to that of base fluid except that it is slightly thicker due to the presence of metal

particles.

3.3.1 Without Magnetic Fields:

In the absence of magnetic field, these metal particles align themselves along the direction

of flow (figure 3(a))

Fig. 3.3.1 Without Magnetic Field



3.3.2 With Magnetic Fields:

When a magnetic field is applied, however, the microscopic particles (usually in the 0.1–

10 μm range) align themselves along the lines of magnetic flux. Thus a chain like structure

is formed along the line of magnetic flux which offers mechanical resistance to the flow

resulting in an increase in the viscosity of fluid.

Fig 3.3.2 With Magnetic Fluid

With increase in the intensity of the magnetic field, the shear stress increases continuously.

With the increment in shear stress, the fluid starts to behave like semi solid.



Chapter 4.

4.1 CHEMICAL COMPOSITION

A typical MR fluid consists of 20%–40% by volume of relatively pure, soft iron particles,

typically 3–5 microns, suspended in a carrier liquid such as mineral oil, synthetic oil, water,

or glycol. A variety of proprietary additives similar to those found in commercial lubricants

are commonly added to discourage gravitational settling and promote particle suspension,

enhance lubricity, modify viscosity, and inhibit wear.

4.2 PHYSICAL PROPERTIES

MR fluids made from iron particles exhibit maximum yield strengths of 30–90 KPa for

applied magnetic fields of 150–250 kA/m. MR fluids are not highly sensitive to moisture

or other contaminants that might be encountered during manufacture and use. Further,

because the magnetic polarization mechanism is not affected by the surface chemistry of

surfactants and additives, it is a relatively straightforward matter to stabilize MR fluids

against particle-liquid separation in spite of the large density mismatch. The ultimate

strength of the MR fluid depends on the square of the saturation magnetization of the

suspended particles.

4.3 WHAT MAKES A GOOD MR FLUID?

The most common response to the question of what makes a good MR fluid is likely to be

"high yield strength" or "non-settling". However, those particular features are perhaps not

the most critical when it comes to ultimate success of a magneto rheological fluid. The

most challenging barriers to the successful commercialization of MR fluids and devices

have actually been less academic concerns.



Chapter 5.

5.1 ADVANTAGES

Functionality

The damping system uses onboard electronics.

No additional operator control is required.

MR provides real-time controllability.

System Integration

Additional electronic controls are easily adaptable to the existing machine’s

electronics footprint.

Easy To Control

As magnetic field can be precisely controlled by driven Electromagnets

Have higher magnitude of Yield Stress

20-50 times stronger than ER fluids



5.2 Disadvantages /Limitations.

5.3 High density, due to presence of iron makes them heavy.

High quality fluids are expensive.

Fluids are subjected to thickening after prolonged use and need replacing.

Settling of Ferro-particles can be a problem for some application.



Chapter 6

APPLICATIONS

6.1 MR fluid as robot blood.

Astronauts onboard the International Space Station are studying MR fluids that might one

day flow in the veins of robots.MR fluids are liquids that harden or change shape when

they feel a magnetic field.

Fig 6.1 Robot with veins filled with MR fluids.



6.2 Mechanical Engineering.

Scientists and mechanical engineers are collaborating to develop stand-alone seismic

dampers which, when positioned anywhere within a building, will operate within the

building’s resonance frequency, absorbing detrimental shock waves and oscillations within

the structure, giving these dampers the ability to make any building earthquake-proof, or

at least earthquake resistant.

6.3 Civil Engineering.

Civil engineers in the construction industry are incorporating MR Technology into the

structural engineering of buildings and bridges. The system is relatively inexpensive, needs

little maintenance and requires very little power to operate.

In giant bridges stay cables are prone to vibration due to wind and rain effects. Smart

dampers have the potential efficiency several times that of standard oil dampers. MR

Dampers are currently being used on the Dongting Bridge in China.

Fig. 6.3 Giant bridges with MR dampers in between stay cables

6.4 Optics.

Magneto-Rheological Fluid was used in the construction of the Hubble Space telescope’s

corrective lens.



6.5 MR fluid in seat suspensions.

Mainly used in heavy in heavy industries with application such as heavy motor damping,

operator seat/cab damping in construction vehicles. Seating equipped with MR dampers is

the only product that offers both safety and health benefits for drivers. Unlike standard air

suspended seats, which compromise shock and vibration control, the MR technology is the

only solution that automatically adapts to both the driver’s body weight and continually

changing levels of shock and road vibration, improving driver responsiveness and control

while reducing fatigue and risk of injury.

Fig. 6.5 Seat suspension filled with MR fluids.



6.6 MR fluid in washing machines.

A good example of unwanted vibratory motion is a washing machine in its spin cycle trying

to walk out of the room. MR damping can correct this and other problem vibrations.

Washing machine represents a standard compromise between controlling vibration

associated with the spin cycle and achieving optimum system performance and efficiency.

Fig. 6.6 Washing Machine filled with MR fluids.



6.7 MR fluid in automotive suspensions.

Shock absorber of a vehicle suspension are filled with Magneto-Rheological fluid instead

of plain oil or gas. Magneto rheological fluids to provide real-time optimization of

suspension damping characteristics that improve ride and handling.

Fig. 6.7 Automotive Suspension filled with MR fluids.



6.8 Human prosthesis

Magneto rheological dampers are utilized in semi-active human prosthetic legs. Much like

those used in military and commercial helicopters, a damper in the prosthetic leg decreases

the shock delivered to the patient’s leg when jumping, for example. This results in an

increased mobility and agility for the patient.

Fig. 6.8 Artificial Human leg filled with MR fluids.



7. CONCLUSION

MR fluids can be considered as a better way of controlling vibrations.

Magneto rheological fluids are actually amazing magnetic fluids.

MR fluid durability and life have been found to be more significant barriers to

commercial success than yield strength or stability.

Amenability of a particular MR fluid formulation to being scaled to volume

production must also be considered.

Challenges for future MR fluid development are fluids that operate in the high shear

regime of 104 to 106 sec-1.

The key to success in all of these implementations is the ability of MR fluid to

rapidly change its rheological properties upon exposure to an applied magnetic

field.



8. REFRENCES

1. “Magneto rheology of submicron diameter iron micro wires dispersed in silicone oil.”

R.C. Bell, J.O. Karli, A.N. Vavereck, D.T. Zimmerman. Smart Materials and Structures,

17 (2008) 015028.

2. “Study on the mechanism of the squeeze-strengthen effect in Magneto rheological fluids

" X. Z. Zhang, X. L. Gong, P. Q. Zhang, and Q. M. Wang, J. Appl. Phys. 96, 2359 (2004).

3. T. Simon, F. Reitich, M. R. Jolly, K. Ito, and H. T. Banks (2001) “On the Effective

Magnetic Properties of Magneto rheological Fluids,” Mathematical and Computer

Modelling.

4. M.R. Jolly (1999) “Properties and Applications of Magneto rheological Fluids,”

(Invited) Proc. of MRS Fall Meeting, Vol. 604, Boston, MA, Nov. 29-Dec. 3, 1999.

5. J. D. Carlson, “Low-Cost MR Fluid Sponge Devices,” J. Intelligent Systems and

Structures, 10 (1999) 589-594.

6. J. David Carlson, “New Cost Effective Braking, Damping, and Vibration Control

Devices Made with Magnetorheological Fluid,” Materials Technology, 13/3 (1998) 96-99.

7. A. J. Margida, K. D. Weiss and J. D. Carlson, “Magnetorheological Materials Based on

Iron Alloy Particles,” Int. J. Mod. Physics B, 10 (1996) 3335-3341.