Magneto-Rheological (MR) Fluids

Harish HiraniAssociate ProfessorDepartment of Mechanical EngineeringIndian Institute of Technology DELHI

Lubrication & Bearings http://web.iitd.ac.in/~hirani/

MagnetoRheological Fluids

Dr. H. HiraniMechanical Engnieering, IIT Delhi

Used in Japan's National Museum of Emerging Science & China's Dong Ting Lake Bridge to counteract vibrations caused by earthquakes and gusts of wind

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

RheoLOGY= Science of material flow under external load conditions

MAGNETOrheological FLUID= Fluid, whose apparent viscosity increases, with application of MAGNETIC field.

Liquids that harden or change shape when they feel a magnetic field

Carrier liquid

Soft magnetic particles

Application of magnetic field, polarizes and align magnetic particles. Particle chain formation limits particle movement, which in turn limits the movement of the fluid.

Particle Sizes !!!!!

Consist micron (1-10 μm) sized, magnetically polarizable (soft magnets) dispersed in a carrier liquid such as mineral, silicone oils, kerosene, water.Particles > 10 μm~ unstable against settling

MR Fluids:

( )ηρρ

92

velocitysettling sStoke'2

P if ga−=

Consist micron (1-10 μm) sized, magnetically polarizable (soft magnets) dispersed in a carrier liquid such as mineral, silicone oils, kerosene, water.Particles > 10 μm~ unstable against settling

MR Fluids:

( )ηρρ

92

velocitysettling sStoke'2

P grf−=

Particles < 1 μm destabilizing effect of Brownian motion dominates

Required Particles’ propertiesPermeability: degree of magnetization of a material that responds linearly to an applied magnetic field.

μ0 (=4π×10−7 N/A2) is known as permeability of free space.

Required Particles’ properties….Relative Permeability

Iron 2000

Nickel 100

Permalloy (78.5% nickel, 21.5% iron) 8000-25,000

Mu metal (75% nickel, 2% chromium, 5% copper, 18% iron)

20,000-100,000

Required Particles’ properties….

Coercivities of soft and hard magnetsMaterial Coercivity

Permalloy, Ni81Fe19 0.5-1

Co 20

Ni 150

Alnico, a common refrigerator magnet 1500-2000

NdFeB 10,000

SmCo5 40,000

The applied field where the data (called a magnetization curve) crosses zero is the coercivity.Saturation Limit: The limit of applied field at which all the magnetic domains align with the field, and the magnetic-curve flattens out.

Material

Approx % Composition

Maximum permeability

Saturation flux density B gauss

Fe Ni Co Mo Other

Iron 99.91 --- --- --- --- 2,000 21,500

Purified iron 99.95 --- --- --- --- 10,000 21,500

Permalloy 21.2 78.5 --- --- 0.3 Mn 100,000 10,700

Mu metal 18 --- --- --- --- 100,000 6,500

Particle sizePermeabilitySaturationNon-magnetic carrier fluid

How many particles ???????

MR Fluids:

20-50% by vol. Magnetic particles (higher vol. Increase “off state” viscosity).

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120 140

Yie

ld S

tress

(kPa

) at

100

(1/s

)

Magnetic Field, H (kA/m)

MRF36L

MRF36S

MRF36M1

MRF36M2

MR Fluid Properties

)/( viscosityelastic , viscosityplastic oaddition tIn fluid,Newtonian -non

0 γτγηττ

&

&+= o

viscosityplastic is fluid,Newtonian ηγητ &=

Fluids do not flow until the applied shear stress crosses a threshold value called the “yield stress”.

γτη &=′iscosity Apparent v

0

10

20

30

40

50

60

70

80

90

0 250 500 750 1000

Off

-sta

te v

isco

sity

of M

R fl

uids

(Pas

)

Shear Rate (1/s)

10% by Volume Iron particle

36% by Volume Iron particle

γτη &=′iscosity Apparent vSpecial consideration for

high shear rate application

MR-FLUID…………..Make device smart by changing system’s properties( stiffness, damping, viscosity, shear modulus) in a desirable manner. Sy ~ 0-100 kpa

Useful in active control of vibration & motion, i.e. engine mount, shock absorbers, seat dampers, variable resistance equipment, etc.

Motion damping is perhaps the most practical use for MR technology today

Property MR fluids ER fluidsMax. yield stress τ0 50-100 kpa 2-5 kpa

Maximum field ~250 kA/m ~4 kV/mm

Apparent plastic viscosity η 0.1-10 pa-s 0.1-10 pa-s

Operable temp. range -40-150 oC +10-90 oC

Stability Unaffected by most impurities

Cannot tolerate impurities

Density 3-4 g/cm3 1-2 g/cm3

Maximum energy density 0.1 Joules/cm3 0.001 Joules/cm3

Power supply (typical) 2-50 V, 1-2 A 2000-5000 V, 1-10 mA

MR Fluids:20-50 times stronger than ER fluids, lower

sensitivity to impurities.

MR fluid MRF-132LD MRF-240BS

MRF-336AG

Fluid base Synthetic oil Water Silicone oil

Operable temp. range oC -40-150 0-70 -40-150

Density (g/cc) 3.055 3.818 3.446

Weight percent solids 80.74% 83.54% 82.02%

Coefficient of thermal expansion 0.55-0.67×10-3 0.223×10-3 0.58×10-3

Specific heat @ 25oC(J/g oC)

0.80 0.98 0.68

Thermal conductivity (w/w oC) 0.25-1.06 0.83-3.68 0.20-1.88

Flash point (oC) > 150 >93 > 200

Viscosity @ 10s-1/50s-1

(Pa-sec)0.94/0.33 13.6/5.0 8.5

Properties of three different types of MR fluids

Geometries for MR Fluid• Most devices that use MR fluids can be

classified as having:– Fixed poles (Pressure driven flow mode)

• Servo-valves, dampers and shock absorbers

– Relatively moveable poles (Direct-shear/sliding mode). • Clutches, brakes, chucking and locking devices.

Both of these configurations can be described by assuming MR fluidis dispersed between two parallel plates. In the sliding plate (orshear) mode the MRF is stationary and the walls/electrodes move. Inthe fixed plate (or flow) mode the walls/electrodes are stationary andthe fluid moves.

Squeeze-film mode Low motion and high force applications

dzdxdzdydxxppdzdxdy

ydzpdy .... :balance Force τττ +⎟

⎠⎞

⎜⎝⎛

∂∂

+=⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

++

Small element ofFluid with sides

dx, dy, and dz

xP∂∂

=∂∂

=∂∂

y mode flow Pressure

0y

mode flowShear

τ

τ

In friction brakes, two surfaces are pressed together with a normal force to create a friction torque.

• Disk brake: Flat surface ⊥ to axis of rotation, and normal force is axial.

• Drum brake: Cylindrical surface with normal force in radial direction

Application of MR Fluid in Brakes?

Maximum contact pressure,b

pmax

Maximum bulk temperature,tm, max

Friction materialaCoefficient of

friction, µ psi kPa °F °CMoldedWovenSintered MetalCorkWoodCast iron; hard steel

0.25-.0450.25-0.450.15-0.450.30-0.500.20-0.300.15-0.25

150-30050-100150-300

8-1450-90

100-250

1030-2070345-690

1030-207055-95

345-620390-1720

400-500400-500

400-1250180200500

204-260204-260232-677

8293260

aWhen rubbing against smooth cast iron or steel.bUse of lower value will give longer life.

At least one the friction surface is metal (cast iron or steel) and other is usually a high friction material, referred to as lining. Sacrificial.

Properties of Braking materials Operating in Oil

Friction materiala Coefficient of friction, µMoldedWovenSintered MetalPaperGraphiticPolymericCorkWoodCast iron; hard steels

0.06-0.090.08-0.100.05-0.080.10-0.140.12 (avg)0.11 (avg)0.15-0.250.12-0.160.03-0.16

aWhen rubbing against smooth steel or cast iron.

Brake wiping mechanism !!!!!

3/14/2014 27

MRF Bearing cum Brake

1

11

21

31

41

51

61

71

81

91

0 0.2 0.4 0.6 0.8 1 1.2

Current, A

Am

plifi

catio

n fa

ctor

200 RPM

1200 RPM

0=

==i

Ii

TT

AF

hr

ydωηττ +=

drh

rrwdrh

rrhTr

ryd

r

ryd ∫∫ ⎟

⎠⎞

⎜⎝⎛ ++⎟

⎠⎞

⎜⎝⎛ +=

3

2

2

1

222 ηωτπηωτπ

( ) ( ) ( ) ( )32

33

22

23

31

32

21

22 3

2342 rr

hwrrwrrrrhT ydyd −+−+−+−= ηπωτπηπωτπ

3/14/2014 29

MR BrakeTitle: Magnetorheological brake operating under shear, squeezing and valve mode.

Inventor: H. Hirani and C. Sarkar

Application number: 2530/Del/2013

Application of MR Fluid in Dampers?

• The practical necessities often require attenuation of the vibrations.– Passive Damper– Active Damper– Semi-active Damper

Application of MR Fluid in Engine Mount?

Basic Function: To connect the Engine firmly to Chassis / Frame. Vibration isolation, to reduce vibrations transmitted from the engine to the frame.

Damper IsolatorAttacks the source of vibration and reduces the movement of vibration source.

Prevents the transmission of vibration from the vibration source to another part.

Mount Advantages Disadvantages

Passive Easy to design, availability, shows better performance at tuned frequency

Can’t change response as per change in input frequency.

Active:Electromechanical actuators, piezoelectric elements along with closed loop feed back system.

Ability to adapt to varying operating conditionsOptimizing the mount effectiveness under all conditions.

Costs.Failure of any component brings system to stand still condition.

Semi-active: combination of the active and passive isolator

Even though the actuation or feed back system fails it functions as a passive mount serving the purpose.

Cost higher than the passive type of mount.

Frequency

Dyn

amic

Stif

fnes

s

Dynamic Stiffness of an ideal engine mount

Application of MR Fluid in Engine Valves• Ex: In most of engines, the valve timings and lift are

optimized for one set of operating conditions. – engine operates in various load and speed

conditions. Consequently, to optimize the engine performance in any condition and any circumstance, a need exists for a device that permits variable valve actuation.

– Variable lift/timing (VVA) to exploit benefits:• Fuel economy• Elimination of throttling • Reduction in emission.

Reference: SAE 1999-01-0329, SAE 2003-01-0029, SAE 2003-01-0036, SAE 2003-01-0052, SAE 2004-01-1386, ..

Natural frequency …. 9000 rpm

Tribo-Pairs: • Cam-pushrod• pushrod-rocker arm• rocker arm-rocker shaft• rocker arm-valve • valve-valve-guide • valve-seat• push rod – guide

3/14/2014 Total slides = 27 38

Variable Lift Valve Mechanism

Valve lift vs crank rotation

56789

1011

0 120 240 360 480 600 720 840 960 1080

Crank rotation, degrees

Valv

e lif

t, m

m

1.7 Amp current

1 Amp current

0 amp

3/14/2014 39

Delta converte

r

AC Motor4 Stroke Diesel engine

ValveDc

Power supply

Electro Magnet

Optical Displacement sensor

Computer

Maximum valve lift Vs Product of speed and Current

5.56

6.57

7.58

8.59

0 200 400 600 800

Product of Cam speed(Rpm) and Current(Amps)

Max

imum

Val

ve li

ft(m

m)

Experimental valuesLeast square fit

Valve_Lift = 0.0021(N.I) + 6.6646

Variable spring stiffness ……….

Thank U