Magnetorheological fluid is a type of smart fluid that can quickly change its viscosity and yield stress when exposed to a magnetic field. It consists of micrometer-sized iron particles suspended in a carrier fluid. When a magnetic field is applied, the iron particles form chains that link together and act like a solid. MR fluid is currently used in vehicle dampers, clutches, washing machine dampers, prosthetic limbs, and seismic dampers in buildings. It offers fast response time, precise control, and high force output. While costly, MR fluid is advantageous over other smart fluids due to its higher yield stress, lower power needs, and insensitivity to environmental factors.
2. ◈ Discovered by Rabinow in 1940s at US National Bureau of Standards
◈ MR Dampers currently being used in Dongting bridge, China
◈ Famously used in suspension of the 2002 model of the Cadillac Seville STS
automobile and more recently, in the suspension of the second-generation Audi
TT.
Background
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3. Smart Fluids
◈ By using magnetic or electric field, it is possible to change properties of fluid
◈ The most developed smart fluids today are fluids whose viscosity increases when a
magnetic field is applied.
◈ Electrorheological or ER fluids are another type of smart fluid in which the
resistance to flow can be changed quickly and drastically by an applied electric
field.
◈ In the presence of an electric field, other smart fluids modify their surface tension.
This technique has been used to create extremely small, controlled lenses.
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5. Introduction
◈ A Magneto-Rheological fluid (MR
Fluid) is a type of smart fluid in a
carrier fluid, usually a type of oil.
◈ Viscosity increases, with application
of magnetic field, and thus becomes a
viscoelastic solid
◈ It is a Newtonian fluid in off state and
Non-Newtonian fluid in on state
◈ By adjusting the magnetic field
intensity, the yield stress of the fluid
in its active ("on") state may be
regulated very precisely.
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6. Composition
◈ Carbonyl Iron Particles: These soft iron particles, which are only 3 to 5 micrometers
in diameter, make up 20 to 40% of the fluid(different from Ferro particles).
◈ Carrier Liquid: The iron flakes are suspended in a liquid, most often hydrocarbon
oil.
◈ Proprietary Additives: These chemicals are used to prevent the iron particles from
settling due to gravity.
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7. Working of MR Fluid
◈ These are the fluids that change their
properties when we apply a magnetic
field to them
◈ When the magnet is in place of MR
fluid, it turns into a solid
◈ When the magnet is removed from
the solid, it instantly reverses into
liquid
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8. Working
Fig a) shows the random distribution of
magnetic particles in MR fluid.
Fig b) shows the behaviour of magnetic
particles in a magnetic field
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9. Characteristics of MR Fluid
Properties of MR Fluid Typical Value
Initial Viscosity 0.2 – 0.3 [Pa-s] (at 25°C)
Density 3 – 4 [g/cm3 ]
Magnetic Field Strength 150 – 250 [kA/m]
Yield Point 50 – 100 [kPa]
Reaction Time Few milliseconds
Supply Voltage and Current Intensity 2– 25 V, 1–2 A
Work Temperature Range -50 to 150 [°C]
The rheological characteristics of MR fluids are primarily determined by particle size,
concentration, density, and additives. Magnetic properties can also be used to assess the nature
and creation of particle structure within the fluid.
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10. Bingham plastics
◈ Bingham plastics is used to describe
fundamental field dependent fluid
characteristics in most engineering
applications. Shear stress is directly
proportional to shear strain in a
Bingham plastic, which is a Non-
Newtonian fluid whose yield stress
must grow before flow can
commence. The overall yield stress is
calculated as follows:
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12. Flow Mode
◈ Both plates are stationary
◈ Fluid is located between these stationary plates
◈ Magnetic field is perpendicular to the direction of flow
◈ Application: Dampers, MR Valve and shock absorbers
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13. Shear Mode
◈ In this mode, one plate is stationary and the other plate is moving
◈ In this mode also, magnetic field is perpendicular to direction of flow of fluid
◈ Shear mode is generally used to control rotational motion
◈ Applications: Clutches and Brakes
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14. Squeeze Mode
◈ In this mode, one plate is moving relative to other, perpendicular to its plate
◈ In this mode also magnetic field is perpendicular to direction of flow of fluid
◈ This mode is used in controlling small, millimetre-order movement but involving
heavy force
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16. Vehicle Suspension Damper
◈ The MR fluid is driven across a built-
in MR valve in the MR damper.
◈ The MR damper's piston functions as
an electromagnet with the needed
number of coils to generate the
required magnetic field.
◈ The MR damper also incorporates a
run-through shaft to eliminate the
need for an accumulator.
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17. MR Transmission Clutches
◈ They are used to transmit torque from
the engine to the transmission and
the car in the automobile power train.
◈ The MR sponge clutch can be utilized
to offer vehicle launch control,
resulting in a smooth vehicle launch.
◈ As a result, the MRF clutch may be
used to replace conventional torque
converters, resulting in improved fuel
economy.
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18. MR Damping in Washing Machine
◈ During the spin cycle of a household
washing machine, a variable damping
system based on magnetorheological
fluid sponges can help manage the
vibratory motion.
◈ Damping is turned on as the drum
approaches resonance and turned off at
the fastest speeds for the best vibration
isolation.
◈ The method allows the drum to rotate at
high enough speeds to act as a
centrifuge, but without the violent
shaking that every user is accustomed
with.
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19. MR Technology used in Prosthetic Limbs
◈ Biedermann Motech, a German maker of prosthetic
components, collaborated with design engineers to
create a device that increases the mobility of above-
the-knee leg amputees.
◈ The ProliteTM Smart MagnetixTM Above-the-Knee
(AK) Prosthetic uses controlled MR technology
developed from the LORD Motion MasterTM Ride
Management System truck seat damper to improve
gait balance, stability, and energy efficiency.
◈ IoT makes it even more effective
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20. MR Fluid in Seismic and Wind Mitigation
◈ Civil engineers are applying MR Technology into the structural engineering of
buildings and bridges in the construction sector.
◈ A dampening system using MR fluid dampers protects the structure against
earthquakes and windstorms in the same way as an automotive shock absorber
does.
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21. Other Applications
◈ Military and Defense: The Army Research Office in the United States is now
financing research into the use of MR fluid to improve body armor. Researchers
estimated that making the fluid bullet resistant would take five to ten years in 2003.
Dynamic MR shock absorbers and/or dampers are also used in HMMWVs and
other all-terrain vehicles.
◈ Optics: Magnetorheological finishing, a magnetorheological fluid-based optical
polishing technology, has shown to be extremely accurate. It was utilized to make
the corrective lens for the Hubble Space Telescope.
◈ Aerospace: In the case of a crash, magnetorheological dampers are being
developed for use in military and commercial helicopter cockpit seats as safety
mechanisms. They would be used to reduce the amount of stress imparted to a
passenger's spinal column, lowering the risk of lasting harm in the event of a
collision.
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22. MR Fluid vs ER Fluid?
◈ MR Fluids can change their rheological properties far easily than ER Fluids
◈ MR fluids can be used in dirty or humid atmosphere since they are less sensitive to
moisture and contaminants
◈ Power and voltage required as compare to ER fluid are less for MR fluid
◈ MR fluid does not affected by surface chemistry of surfactant used.
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23. Advantages
◈ Easy to control
◈ It is a high quality fluid
◈ Higher magnitude of yield stress
◈ Fast response
◈ Low power requirement
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24. Disadvantages
◈ They are heavy due to their high density, which is caused by the presence of iron.
However, because operational quantities are minimal, this is not an
insurmountable barrier.
◈ High quality fluids are costly.
◈ After a long period of use, fluids thicken and must be replaced.
◈ For some applications, Ferro-particle settling can be an issue.
◈ Extremely high/low temperatures make it impossible to operate.
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25. Conclusion
◈ The MR Fluid, will replace the conventional based mechanisms, and it also
improves in cost reduction and functionality of the system.
◈ MR Fluid has a wide range of applications and there is a lot of future scope for
these technology.
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26. References
◈ Emerging Trends in Mechatronics: Edition-1 Wiley Publications(Aydin Azizi) (Published-
2020)
◈ Magnetorheological Fluid- A review on characteristics devices and applications- Gaurish A
Walke & Amol Patil(Published-2019)
◈ Magnetorheological Fluid and its Applications by Pranav Gadekar , V.S.Kanthale and N.D.Khaire
(Released-2017)
◈ https://www.researchgate.net/publication/322077004_Magnetorheological_Fluids_and_Its_Applic
ations_Current_Scenario_and_Future_Prospects- Hanmanth Saluke & Surendra Thikane (Released
in 2017)
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