disc break

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WELCOME

U.URBAN KUMAR

M.E CAD/CAMIV Sem 2006

A.U

Under the guidanceof

Prof.B.S.K.SUNDARASIVARAO

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Transient thermalanalysis of a disc brakerotor using F.E.A

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AbstractThe present investigation is aimed to study.The given disc brake rotor for its stability andrigidity (for this Thermal analysis and coupledstructural analysis is carried out on a given discbrake rotor).Best combination of parameters of disc brakerotor like Flange width, wall thickness andmaterial there by a best combination is

suggested. (for this three differentcombinations in each case is analyzed)The correlation between Ansys results andexperimental results

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Introduction When a brake is working, the transformation of kinetic energy of moving

masses into thermal energy takes place. Brake elements are heated, whichleads to the deterioration of work conditions of a brake pad, increasing its, wearand decreasing the coefficient of friction. Therefore, the limitation of brakeheating is one of the important problems in the calculation and constructionbrake blocks, and in certain cases the thermal calculation defines the choice of

a brake. When the construction of brake systems is being designed, it is

necessary to know the temperature and the thermal distortion of the interface inthe frictional contact region. The analytical definition of heating parametersmust take into account the condition under which the mechanism must work.Thus, in intensive momentary braking the radiation of heat into thesurroundings may be neglected. Then since the brake pads are made ofmaterials with low thermal conductivity, almost all the heat generated in friction

is directed inside the disk. In view of the short duration of the braking process,the heat generated has no time to heat all the disk and, hence, the temperatureof the disk working surface is considerably higher than the mean value of thevolume temperature.

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BRAKE A brake is a device by means of which artificial frictional

resistance is applied to moving machine member, inorder to stop the motion of a machine.

In the process of performing this function, thebrakes absorb either kinetic energy of the movingmember or the potential energy given up by objects beinglowered by hoists, elevators etc., the energy absorbed bybrakes is dissipated in the form of heat. This heat isdissipated in the surrounding atmosphere.

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DISC BREAK

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Working of Disc brake The principle used is the applied force (pressure) acts on the brake pads, which comes in tocontact with the moving disc. At this point of time due to friction the relative motion isconstrained.

A moving car has a certain amount of Kinetic energy and the brakes have to remove this energyfrom the car in order to stop it.

Each time the car is stopped, the brakes convert Kinetic energy to heat generated by the frictionbetween the pads and the disc slows the disc down.

When the brakes are applied, hydraulically actuated pistons move the friction pads in to contactwith the disc , applying equal and opposite forces on the later. On releasing the brakes therubber-sealing ring acts as return spring and retract the pistons and the friction pads away fromthe disc

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ail Following

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Definition of problem: Due to the application of brakes on the car disc brake rotor, heat generation

takes place due to friction and this temperature so generated has to beconducted and dispersed across the disc rotor cross section. The condition ofbraking is very much severe and thus the thermal analysis has to be carriedout.

Linear thermal analysis is performed to obtain the temperature field since

conductivity and specific heat of the material considered here are independentof temperature. The analysis performed here is transient thermal analysis astemperature distribution varies with time. (The time for thermal analysis istaken as 4.8 seconds of braking)

An Ansys thermal model was developed to predict temperatures throughthe brake corner. The model includes the brake disc, pads, caliper, wheel,spindle and axle in order to accurately predict brake system temperaturesduring long braking and heat soaking conditions. In addition, the model can be

used to predict the brake fluid temperature rise. Various aspects of the brakethermal analysis process are schematically summarized in fig below.

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Brake Thermal Analysis Process fora Vehicle Under a Given BrakingSchedule

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Boundary conditions Geometry boundary conditions: The temperature 250 C is fixed at the hub bore grinds as the

boundary conditions. The standard convection law is used. Thermal Boundary conditions:

i) A convection boundary condition is applied on all sides ofthe axis symmetric model except in the region of tread and thehub. The heat transfer coefficient of 50 W/m2k is considered.

ii) The thermal load is applied axis symmetrically on thetread of the wheel is a heat flux (q) of value 75e4 W/m2 and isanalyzed for 4.8 seconds of braking i.e. the heat generate is

going to be distributed along the profile after the application ofthe brakes .

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ASSUMPTIONS

The analysis is done taking the disc brake efficiency as 30% (since thedistribution of the braking torque between the front and rear axle is 70:30)

Brakes are applied on all the four wheels. The analysis is based on pure thermal loading and vibrations and thus only

stress levels due to the above is done. The analysis does not determine the lifeof the disc brake. Only ambient air-cooling is taken in to account and no forced convection is

taken. The kinetic energy of the vehicle is lost through the brake discs i.e. no heat loss

between the tyres and the road surface and the deceleration is uniform. The disc brake model used is of solid type and not the ventilated one. The thermal conductivity of the material used for the analysis is uniform

throughout. The specific heat of the material used is constant throughout and does not

change with the temperature.

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CALCULATION

Given Data:Velocity of the vehicle = 96.6 k.m.p.h = 26.833 m/sTime for stopping the vehicle = 4.8 secondsMass of the vehicle = 1000 kg.Step-1:

Kinetic Energy (K.E) = * m * v2= * 1000 * 26.8332

= 360 KJThe above said is the Total Kinetic Energy induced while the vehicleis under motion.Step-2:

The total kinetic energy = The heat generated but the heatgenerated in one of the wheel of the car is 1/3rd the total kineticenergy.[2]i.e. this 28.6 K. Cal/ft2 hr.1 Cal = 1/252 Btu& 1 Btu = 1.05504 KJ

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Step-3: The area of the rubbing faces

A = (r12-r2

2) = (0.145622 0.10362)

A = 329x10-4 m2

Step-4:

The density of heat flow (Heat Flux) directed in to the disc.

Heat Flux= heat generated = 120

area of contracting surfaceXbreaking time 329X10-4 X4.8

q = 750000 w/m2

05504.1252

10006.28

Q

CALCULATION cont..

= 120 KJwhich is 1/3rd the total kinetic energy.

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Geometric Model of a Disc Brake

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CAST IRON ALUMINIUM

STEEL

Thermal Co-efficient of

expansion ( xx) /0 C

11e-6 23e-6 12e-6

Thermal Conductivity

(K)

W/mk

50 228 73

Specific Heat (Cp)

J/Kg K450 938 460

Thermal Material Properties of CI, Al & Steel

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All applied boundary conditions

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Temperature distribution forCast Iron 8mm flange width

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Temperature distributionfor Cast Iron10mm flange width

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Temperature distribution forAluminum 10mm flange width

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Temperature distribution forSteel 10mm flange width

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.Temperature Vs Distance along thecontacting surface of 10mm flangewidth of Cast Iron in X-direction.

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Temperature Vs Distance along the contactingsurface of 10mm flange width of Cast Iron in

Y-direction.

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Flange width Vs Temperaturefor CAST IRONFlange width Vs Temperature

196

198

200

202

204

206

8 10 12 14

Flange width (mm)

Temperature(degcelsius)

Max temp

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Max Temperature Vs Flange widthfor ALUMINIUMMax Temp Vs Flange width

0

50

100

150

200

8 10 12 14

Flange width (mm)

T

emperature(deg

celsius)

Max Temp

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Max Temperature Vs Flangewidth for STEEL

Max temp Vs Flange width

168170

172174176

178180182

184186

8 10 12 14

Flange width (mm)

T

emperature(deg

celsius)

Max temp

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Results of maximum

Temperatures attained

Flange widthIn mm

CAST IRON

In oCALUMINIUM

In oCSTEEL

In oC

8 198.698 171.567 183.494

10 203.912 156.701 181.062

12 202.286 143.904 176.982

14 201.407 134.689 174.470

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the maximum temperature attained

for different flange widths and for

different materials.

For Cast Iron Disc, the maximum temperature is attained for a flangewidth of 10mm, which is 203.912 C. This temperature value is nearestto the experimental value of 215 C . The temperature variation fordifferent flange width is as shown in the Graph.

For Aluminum Disc, the maximum temperature is attained for a flange

width of 8mm, which is 171.567C. The temperature variation fordifferent flange width is as shown in the Graph

For Steel Disc, the maximum temperature is attained for a flange width of8mm, which is 183.494C.

The temperature variation for different flange width is as shown in theGraph

From the above results we can conclude that the Cast Iron Disc of flangewidth 10mm nears to the experimental value, hence this isrecommended.

Moreover the temperature distribution on the contacting surface alongX direction and Y direction is as shown in the Graphs

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Structural material propertiesof Ci, Al & SteelProperties Material Cast iron Aluminum Steel

1.YOUNGS MODULUS (E)Gpa

180 170 200

2. POISSONSRATIO (V)

0.25 0.25 0.25

3. COEFFICIENT OF THERMAL

EXPANSION () /oC

11e-6 23.4e-6 12e-6

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Stress in X-direction for CastIron 10mm flange width

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Stress in Y-direction for CastIron 10mm flange width

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1st Principal Stress for Cast Iron10mm flange width.

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2nd Principal Stress for CastIron 10mm flange width.

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Vonmises stress for Cast Iron10mm flange width

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Vonmises stress for CastIron 14mm flange width

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Vonmises stress for Aluminum8mm flange width

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Vonmises stress for Steel 8mmflange width

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Vonmises stress Vs Flange width forCast IronVONMISES STRESS Vs FLANGE WIDTH (CAST

IRON)

0

50

100

150

200250

8 10 12 14

FLANGE WIDTH (mm)

VO

NMISESSTRES

(MPa)

Series1

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Vonmises stress Vs Flangewidth for AluminumVONMISES STRESS Vs FLANGE WIDTH (ALUMINIUM)

0

20

40

60

80

100

8 10 12 14

FLANGE WIDTH (mm)

VON

MISESSTRESS(MPa

Series1

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Vonmises stress Vs Flangewidth for SteelVONMISES STRESS Vs FLANGE WIDTH (STEEL)

0

50

100

150

200

8 10 12 14

FLANGE WIDTH (mm)

VON

MISESSTRESS

(MPa

Series1

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Result s of various stressesobtained for CI, Al & Steel.Sl

No.Material

Flange

width in

mm

Stress in

XDirection

mpa

Stress in

Y-direction

mpa

1st

principal

stress mpa

2nd

principal

stress mpa

Vonmises

stress mpa

1. CAST IRON

8 mm 40.4 59.7 62.6 26.5 230

10 mm 80.1 69.8 81.0 68.8 222

12 mm 70.6 73.2 85.8 48.5 20614 mm 62.2 21.1 62.2 20.8 179

2. ALUMINIUM

8 mm 24.8 7.73 24.8 5.23 48.6

10 mm 31.3 7.55 31.3 7.12 63.7

12 mm 35.2 9.41 35.2 9.04 75.7

14 mm 36.6 11.9 36.6 11.7 84.2

3. STEEL

8 mm 52.0 13.3 52.0 10.6 106

10 mm 62.6 14.7 62.6 13.8 137

12 mm 66.0 17.4 66.0 16.7 157

14 mm 63.3 21.0 63.3 20.7 169

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the variation of stress for differentmaterials having different flangewidths. For Disc made of Cast Iron, maximum Vonmises stress is observed for

8mm flange width which is 230Mpa and minimum Vonmises stress isobserved for 14mm flange width which is 179 MPa.

For Disc made of Aluminum, maximum Vonmises stress is observedfor 14mm flange width which is 84.2MPa and minimum Vonmises

stress is observed for 8mm flange width which is 48.6 MPa. For Disc made of Steel, maximum Vonmises stress is observed for

14mm flange width which is 169MPa and minimum Vonmises stress isobserved for 8mm flange width which is 106 MPa.

Hence it is seen that the Vonmises stress decreases with increase inflange width for Cast Iron Disc and increases with increase in flangewidth for Steel and Aluminum Discs

Viewing the above results and the discussion made in this chapterregarding the material of the Disc Brake we can conclude that the CastIron Disc of 10mm flange width can be preferred.

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CONCLUSIONS The following conclusions are drawn from the present work. An axis-symmetric analysis of disc brake has been carried out using plane77

and plane 82 through ANSYS R 5.4 (F.E.A) software. A transient thermal analysis is carried out using the direct time integration

technique for the application of braking force due to friction for time duration of4.8 seconds.

The maximum temperature obtained in the brake disc is at the contact surfaceand is observed to be 203.912C for cast iron disc of 10mm flange width, whichvaries only by 5.16% from the experimental value.

Static structural analysis is carried out by coupling the thermal solution to thestructural analysis and the maximum Vonmises stress is observed to be 230MPa for Cast Iron Disc of 8mm flange width.

The brake disc design is safe based on the strength and rigidity criteria.

Comparing the different results obtained from the analysis, it is concluded thatdisc brake with 10 mm flange width, 6.5 mm wall thickness and of material castiron is the best possible combination for the present application.

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disc break

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