‘WEAR ANALYSIS OF A DISC BRAKE

ASSEMBLY’

MOHD DZULFA BIN ABDUL RASHID830920-03-5613

SUPERVISOR:DR. AB RAHIM BIN ABU BAKAR

OUTLINE

INTRODUCTIONOVERALL SCHEME OF THE PROJECTWEAR EQUATION CONTACT PRESSURESIMULATION APPROACHSIMULATION RESULTSCONCLUSIONSFUTURE WORKS

– Pads work with a very thin layer of its own material and generate a semi-liquid friction boundary that creates the actual braking force. (Tamari et al, 2000)

– The needs of high durability and high kinetic friction coefficient must been balanced to make sure the brake pad operating at a desirable condition.

Hard lining material can caused damage to the rotor.

Soft lining material can reduced pad life span

High kinetic friction coefficient can increase squeal propensity.

INTRODUCTION

INTRODUCTION

"Metal-to-Metal" contact is a condition where the shoe rubs directly against the rotor when the lining wears down to the metal brake of pad. Its cause severe damage and loss of braking efficiency (Liu et al, 1979).

Pad completely worn out

BRAKE PAD LINING LIFE SPANCan be determined in two common ways: mileage or year

Driving PatternA highway or motorway-brakes pad last up to 60,000 milesBusy traffic or city-between 25,000 to 30,000 miles

Load TransferredFront brakes pad-last between 30,000 and 60,000 milesrear brakes pad last between 40,000 to 70,000 miles.

INTRODUCTION

List of the minimum thickness allowed of brake pad:

1. ‘Brake pads should typically be replaced when approximately 1/8" to of lining remains on the steel backing plate’.

2. ‘Brake pad should be replaced at least 2mm lining left on the pad’.

3. ‘If the lining appears to be 25% from it original thickness, replacement is needed’.

4. ‘Pad lining should be replaced if the friction material has worndown to a thickness of 1.6mm above the shoe platform.

5. ‘Pad material must be replaced when the pad lining not be less than 1.5mm thick at any point’.

BRAKE PAD LINING LIFE SPAN

INTRODUCTION

INTRODUCTION

(a) Two surface rubbing each other(b) Harder surface cut material away from second surface(c) Debris (removed material) changes to three body abrasion(d) Wear debris then acts as an abrasive between the two

surfaces.

(a) (b) (c) (d)

Abrasive Wear

INTRODUCTION

Objective:To determine wear behaviour of a front disc brake assembly using the finite element method.

PROJECT SCOPE:Literature study of various wear equation. Literature study of brake pad which related to the wear.Write a program code to determine the wear rate. Run a simulation of a simple disc brake model.

Run a simulation of an existing finite element model.Study on the wear behaviour of a brake pad.

INTRODUCTION

PSM I

PSM II

OVERALL SCHEME OF THE PROJECT

Study on wear equation and brake pad in term of wear

Write a program code using

MATLAB software

Set-up an existing finite element model (brake line pressure,

rotational velocity, etc)

Data analysis and discussion

Run a simulation

Conclusion and recommendation for

future work

WEAR EQUATIONArchard (1953):

KPvth =∆

cba tVKPh =∆Rhee (1970) :

∆h = wear displacement (m)

K = specific wear rate coefficient (m3/Nm)

P = contact pressure (Pa)

v = slide rate (m/s)

t = running time (sec)

•The exponents, a, b and c depend upon the material combinations and sliding conditions.

•a, b and c is close to unity (Abu Bakar, 2003)

WEAR EQUATIONPavalescu et al (1973):

( )dcvabu FKFKvI 21 +=

The constant K1, K2, a, b, c, and d is the influence of material composition in the composite material.

Iu = h/L, wear intensity (m/m)

F = load (N)

WEAR EQUATION

Ho et al (1971) :

TTTKh−

=∆ ∗

321

PP tLPT =where,

T = melting Temperature

T = near surface temperature

L = load (N)

t = time (s)

P1, P2 and P3 is a constant and it’s difficult to interpret.

CONTACT PRESSURE

Contact pressure should be kept as uniform as possible in order to minimize tapered wearTopography of a brake pad show the contact plateaus rising typically a few microns above the rest of the surface.

General view of the brake pad area and its division into contact plateaus and areas of real contact within the contact plateaus. (Eriksson et al 2001)

CONTACT PRESSUREThese plateaus are based on the more wear resistant constituents of the pad such as fibres and abrasive particles The rough surface topography will cause contact pressure between brake pad and disc did not distribute uniformly at each point.

SIMULATION APPROACH

Generate the FE model and write the program code

Create input file

Perform the simulation

Determine the contact pressure, P at sliding surface.

Calculate the nodal wear∆h = KPvt

Change the model geometry and print out the result hnew = h + ∆h

Replace the earlier geometry with the new one, hnew

End the simulation?

Yes

No

Input the initial parameters

Create new input file

Piston pad

Finger pad

Disc

+ (ve) ∆h

- (ve) ∆h

z

y

Wear displacement only affected on the z-direction.

Simulation approach is based on (Podra et al, 1999) and (Oqvist et al, 2000).

Baseline Parameters

Brake line pressure, P = 1.0 MPa

Sliding time, ∆t = 30 sec

Rotational speed, ω = 6 rad/s

Simulation duration = 600 sec

Constant

Constant specific wear rate coefficient, K = 1.78 e-13 m3/Nm (Jang et al, 2004 )

Effective pad radius, r = 0.11 m

SIMULATION APPROACH

BRAKE DISC FINITE ELEMENT MODEL

SIMULATION RESULT

1. Contact Pressure distribution

(a) New (b) After 2 minutes

•Contact pressure was focused at certain area only and it is due to rough surface of the new brake pad.

SIMULATION RESULT

(c) After 4 minutes (d) After 6 minutes

•After that when wear taking effect contact pressure distribute more uniformly.•But the pressure distribution is still focused at the upper region of pad

SIMULATION RESULT

(e) After 8 minutes (f) After 10 minutes

•Contact pressure slowly starts spreading at lower region •Effect of wear is try to make sure the sliding surface at the pad level at each point •Smooth surface topography is impossible to obtain because of the contact plateaus

SIMULATION RESULT2. Average wear rate, (for continuous

braking)

smeh / 8 57.6 −=∆

h∆

SIMULATION RESULT3. Contact Area 2.552 e-3 m2

SIMULATION RESULT4. Wear Profile (piston pad)

-1.00E-04

-5.00E-05

0.00E+00

5.00E-05

1.00E-04

1.50E-04

2.00E-04

2.50E-04

3.00E-04

3.50E-04

4.00E-04

Pad Surface

Wea

r Pro

file

(m)

new 2 mins 4 mins 6 mins 8 mins 10 mins

SIMULATION RESULT4. Wear Profile (finger pad)

-1.25E-02

-1.24E-02

-1.23E-02

-1.22E-02

-1.21E-02

-1.20E-02

-1.19E-02

Pad Surface

Wea

r Pro

file

(m)

New 2 mins 4 mins 6 mins 8 mins 10 mins

SIMULATION RESULT4. Height Distribution after 600 seconds (piston pad)

1.40E-04

1.50E-04

1.60E-04

1.70E-04

1.80E-04

1.90E-04

2.00E-04

2.10E-04

2.20E-04

Pad Surface

Hei

ght D

istr

ibut

ion

(m)

Leading edge

SIMULATION RESULT4. Height Distribution after 600 seconds (piston pad)

-1.2260E-02

-1.2240E-02

-1.2220E-02

-1.2200E-02

-1.2180E-02

-1.2160E-02

-1.2140E-02

-1.2120E-02

Pad Surface

Hei

ght D

istr

ibut

ion

(m)

Leading Edge

CONCLUSIONS

1. Contact plateaus are one of the factors that cause contact pressure cannot distribute uniformly.

2. Contact area increasing with the period of wear.

3. Wear of lining material takes place when a thin layer of surfaceis removed.

4. Brake pad profile initially scatter throughout interface but distributed uniformly after 10 minutes.

5. Leading edge experienced more wear than trailing edge.

CONCLUSIONS6. Leading edge and outer region of pad are prone to wear.

Area that prone to wearLeading edge Trailing edge

Outer region

FUTURE WORKS1. To achieve better predicted result, simulation should be

considering the temperature effect.

2. Current wear data (average wear rate, ) can be converted into pad life span by considering braking condition.

h∆

THANK YOU

Developed Program Code for Wear Simulation