Disc Brake Assembly

8/10/2019 Disc Brake Assembly

1/10

Belhocine, A., Bakar, A.R.A.B. & Bouchetara, M. / Mechanica Confab ISSN: 23202!"#

$ol. 3, no. 2, A%rila' 20#! "

Structural An( Contact Anal')i) *f +i)c Brake A))ebl' +urin Sinle

Sto% Brakin -ent

Ali Belhocine#, +r.Ab( Rahi Abu Bakar2an( r.Mo)tefa.Bouchetara3

1PhD Student, Faculty of Mechanical Engineering,

University of Sciences and the Technology of OranL.P 1! El " M#$OUE%, USTO &1!!! Oran '$lgeria(

)Senior Lecturer, De*art+ent of $uto+otive Engineering,Faculty of Mechanical Engineering,Universiti Tenologi Malaysia

-1&1! UTM Sudai, 'Malaysia(

&Professor,Faculty of Mechanical Engineering,

University of Sciences and the Technology of OranL.P 1! El " M#$OUE%, USTO &1!!! Oran '$lgeria(

$stractAn automobile disc brake system is used to perform three basic functions, i.e. to reduce speed of a vehicle,to maintain its speed when travelling downhill and to completely stop the vehicle. During these braking

events, the disc brake may suffer of structural and wear issues. It is quite sometimes that the disc brakecomponents fail structurally and/or having severe wear on the pad. Thus, this paper aims to eamine stressconcentration, structural deformation and contact pressure of brake disc and pads during single brakingstop event by employing commercial finite element software, A!"#". The paper also highlights the effects of

using a fied calliper, different friction coefficients and different speeds of the disc on the stressconcentration, structural deformation and contact pressure of brake disc and pads, respectively./ey0ordsDisc $rake, %on &ises "tress, "tructural Deformation, 'ontact (ressure, )inite *lement.

#. Intro(uctionPassenger car disc brakes are safety-critical components whose

performance depends strongly on the contact conditions at the pad-to-rotorinterface. When the driver steps on the brake pedal, hydraulic fluid is pushedagainst the piston, which in turn forces the brake pads into contact with therotor. The frictional forces at the sliding interfaces between the pads and therotor retard the rotational movement of the rotor and the axle on which it ismounted [!. The kinetic energy of the vehicle is transformed into heat that ismainly absorbed by the rotor and the brake pad.

The frictional heat generated on the interface of the disc and the padscan cause high temperature. Particularly, the temperature may exceed thecritical value for a given material, which leads to undesirable effects, such asbrake fade, local scoring, thermo elastic instability, premature wear, brakefluid vapori"ation, bearing failure, thermal cracks, and thermally excitedvibration as referred to [#,$!. %ao and &in [#! stated that there was considerableevidence to show that the contact temperature is an integral factor reflectingthe specific power friction influence of combined effect of load, speed, frictioncoefficient, and the thermo physical and durability properties of the materials


2/10


$ol. 3, no. 2, A%rila' 20#! #0

of a frictional couple. &ee and 'eo [$! reported that uneven distribution of

temperature at the surfaces of the disc and friction pads brings about thermaldistortion, which is known as coning and found to be the main cause of (udderand disc thickness variation )*T+. buakar et al [/! in their recent workfound that temperature could also affect vibration level in a disc brakeassembly. +alvano and &ee [0! simulated thermal analysis on a disc brake witha combination of computer-based thermal model and finite element-basedtechni1ues to provide a reliable method to calculate the temperature rise,thermal stress and distortion under a given brake schedule. Wole(s"a et al [2!performed analysis on the thermo-mechanical behavior of airplane carboncomposite brakes using 34563arc finite element software which allowsaccurate simulation of the transient heat transfer phenomenon coupled to disc

deformations caused by frictional sliding contact. There are three types ofmechanical stresses sub(ected by the disc brake. The first one is the tractionforce created by the centrifugal effect due to the rotational of the disc brakewhen the wheel is rotating and no braking force is applied to the disc. *uringbraking operation, there are another two additional forces experienced by thedisc brake. 7irstly, compression force is created as the result of the forceexerted by the brake pad pressing perpendicular onto the surface of the disc toslow it down. 4econdly, the braking action due to the rubbing of the brake padagainst the surface of the disc brake is translated into frictional or tractionforce on the disc surface which acts in the opposite direction of the discrotation.

disc brake of floating caliper design typically consists of pads, caliper,carrier, rotor )disc, piston, and guide pins. 8ne of the ma(or re1uirements ofthe caliper is to press the pads against the rotor and should ideally achieve asuniform interface pressure as possible. uniform pressure between the padsand rotor leads to uniform pad wear and brake temperature, and more evenfriction coefficients as cited in [9!. :nevenness of the pressure distributioncould cause uneven wear and shorter life of pads. ;t has also speculated thatthey may promote disc brake s1ueal. The interface pressure distributions havebeen investigated by a number of people. Tirovic and *ay [

not validated, three-dimensional model of the disc brake. Tamari et al. [=!presented a method of predicting disc brake pad contact pressure for certainoperating condition by means of experimental and numerical method. Theydeveloped a 1uite detailed model and validated the model by fitting thenumerical deformations of the disc brake components with experimentalresults. >ohmann et al. [?! also presented a method of contact analysis forthe drum and disc brakes of simple three-dimensional models using *;@software package. They showed a sticking and shifting contact area in theirresults. &ike [


3/10


$ol. 3, no. 2, A%rila' 20#! ##

simple, validated three-dimensional finite element model of the pad, and

applied rather simple piston and finger force onto the back plate interface inhis analysis. >e studied the contact pressure distribution at the disc6padinterface, where gap elements were used to represent contact effect.;n this paper, structural analysis is performed on a simple finite element )7Bmodel of a real disc brake assembly to obtain the contact pressuredistributions on the friction pads and the +on 3ises 4tress in disc interface byutili"ing the @4'4 .? 7B software. 4ensitivity study on rotation of the disc,load pattern and coefficient of friction is also performed.

2. inite eleent o(el an( )iulation;n this work, a three dimensional 5* and 7B model consists of a

ventilated disc and two pads with single slot in the middle as illustrated infigure. and figure. #, respectively. The selected material of the disc is %raycast iron 7% 0 with high 5arbon content and the brake pad has an isotropicelastic behavior whose mechanical characteristics of the two parts arepresented in Table . The materials of the disc and the pads are homogeneousand their properties are invariable with the temperature.

1able #: Mechanical %ro%ertie) of the (i)c an( %a(

ro%ertie) +i)c a(

'oung modulus *)%Pa $< PoissonCs ratio + ?.$ ?.#0*ensity D )kg6m$ 9#0? /??

5oefficient of friction ?.# ?.#

iure #. CA+ o(el of the (i)c an( %a() iure 2. - o(el ofthe (i)c an( %a()

commercial 7B software, namely @4'4 )$* is fully utilised tosimulate structural deformation and contact pressure distributions of the discbrake during single braking stop application. oundary conditions are imposedon the models )disc-pad as shown in 7ig. $a for applied pressure on one side


4/10


$ol. 3, no. 2, A%rila' 20#! #2

of the pad and 7ig.$b for applied pressure on both sides of the pad. The disc is

rigidly constrained at the bolt holes in all directions except in its rotationaldirection. 3eanwhile, the pad is fixed at the abutment in all degrees of freedomexcept in the normal direction to allow the pads move up and down and incontact with the disc surface. ;n this study, it is assumed that 2?E of thebraking forces are supported by the front brakes )two rotors as cited in [#!.y using vehicle data as given in Table # and B1s )-)$, braking force on thedisc, rotational speed and brake pressure on the pad can be calculated,respectively.

a*ne )i(e b 14o )i(e)iure 3:Boun(ar' con(ition) an( loa(in i%o)e( on the (i)c%a()

1able 2: $ehicle (ataIte $alue

3ass of the vehicle ,3 [ kg ! $


5/10


$ol. 3, no. 2, A%rila' 20#! #3

The external pressure between the disc and the pads is calculated by the force

applied to the discH for a flat track, the hydraulic pressure is, as referred to[$!G

Where Ac is the surface of the pad in contact with the disc and thecoefficient of friction.

3. Re)ult) an( (i)cu))ion3.#. $on Mi)e) Stre)) (i)tribution

7igure / shows distributions of the e1uivalent +on 3ises stress overbraking period and it is shown that the highest stress occurs at the bolt holes

at the time t I ?.#0s. This is due to the disc having experience in torsion andshear modes. This high stress concentration can cause a rupture to the boltholes.

iure !: Stre)) concentration at the bolt hole)

3.2. Contact %re))ure (i)tribution7igure 0 illustrates contact pressure distributions of the inner pad at

different braking times. ;t shows that the contact pressure increases graduallyand reaches its maximum value of Pmax I .< 3Pa at the end of braking

period. ;t is believed that the rise in pressure on the contact surface can alsocause a rise in the temperature of the disc and wear of the pads. t the leadingside and inner radius of the pad, contact pressure is seen to be highercompared to the other regions. This is due to this area is mostly in contact withthe disc surface. 7igure 2 shows the evolution of contact pressures alongangular positions of the pad. The maximum value of the contact pressure islocated at the leading edge and at the level of the lower edge of the pad.5ontact pressure distributions of the outer pad are depicted in figure. 9. ;tshows that the maximum contact pressure is predicted in the middle of the pad


6/10


$ol. 3, no. 2, A%rila' 20#! #!

with the value of .$ 3Pa. This is much lower than that obtained on the inner

pad.

a t5 0.26 ) b t5 0.6 ) c t5 # )( t52 )

e t5 2.6 ) f t5 3 ) t5 3.6 )h t5 !6 )

iure 6: Contact %re))ure (i)tribution on the inner %a(

0 1 0 2 0 3 0 4 0 5 0 6 00 , 4

0 , 6

0 , 8

1 , 0

1 , 2

1 , 4

1 , 6

1 , 8

Contactpressure[M

Pa]

A n g u l a r p o s i t i o n

L o w e r e d g e

C e n t e r

H i g h e r e d g e

iure 7: $ariation of contact %re))ure) accor(in to the anular

%o)ition in the inner %a(


7/10


$ol. 3, no. 2, A%rila' 20#! #6

a t5 0.26 ) b t5 0.6 ) c t5 # )

( t52 )

e t5 2.6 ) f t5 3 ) t5 3.6 )h t5 !6 )

iure8: Contact %re))ure (i)tribution on the outer %a(

3.!. -ffect of a fi9e( cali%er7or a comparative study, the effect of a fixed caliper )disc with double

pressure is also simulated where it maintains the same boundary conditionsused in the case of a single-piston caliper. 7igure


8/10


$ol. 3, no. 2, A%rila' 20#! #7

different configurations of the total deformation of the model in the final stage

of braking. ;t is clearly seen that the total deformation is slightly decreasedwith the increase of friction coefficient. ;ndeed, the high mechanical advantageof hydraulic and mechanical disc brakes allows a small lever input force at thehandlebar to be converted into a large clamp force at the wheel. This largeclamp force pinches the rotor with friction material pads and generates brakepower. The higher the coefficient of friction for the pad, the more brake powerwill be generated coefficient of friction can vary depending on the type ofmaterial used for the brake rotor. ;f the value of the coefficient of friction isincreased, the disc is slowed down by friction forces which are opposed to itsmovement, and the maximum deformation that it undergoes is less significant.

a 50.26 b 50.30 c 50.36

iure ": 1otal (eforation at the en( of brakin %erio(3.7. -ffect of (i)c )%ee(

7igure ? shows prediction of contact pressure distributions at threedifferent speeds of the disc. ;t is found that contact pressure distribution isalmost identical in all three cases and its value increases with the increase ofthe angular velocity of the disc. This was also confirmed by bu akar et al.[/!. ;t is believed that this increase can create the wear of the pads as they canleave deposits on the disc, giving rise to what is called Jthe third body.J ;t is

noted that the maximum contact pressure is produced on the pad at theleading edge.


9/10


$ol. 3, no. 2, A%rila' 20#! #8

a ; 570 ra(/) b ; 5"0 ra(/) c ; 5#20 ra(/)

iure #0: Contact %re))ure (i)tribution)

!. Conclu)ionThis paper presents structural and contact analysis of a reduced brake

model without considering thermal effects. The analysis is performed usingcommercial 7B software package, @4'4 where the 7B model only consists of adisc and two pads. 7rom the single stop braking simulation it is found thatG

the bolt holes and outer side of the fins could first damage due to highstress concentration for single and double piston case, respectively

contact pressure is predicted higher at the leading side compared to the

trailing side and its value slightly increases with the increase of discrotation speeds

there is no significant change in disc-pad deformation with respect to thevariation of friction coefficient

Reference)[! . A.bu akar, >.8uyang and K.5ao L Interface (ressure Distribution through "tructural

&odificationsM"A* Technical (aper, --01-21000[#! .A. buakar, >. 8uyang, , and &. &i. LA combined analysis of heat conduction, contact pressure

and transient vibration of a disc brake, ;nt. N. +ehicle *esign, 0)6#, )#??= =?-#?2.[$! .4Oderberg, 4.ndersson. L"imulation of wear and contact pressure distribution at the pad1to1rotor

interface in a disc brake using general purpose finite element analysis software, Wear #29 )#??=

##/$F##0.[/! 5.>. %ao and .Q. &in. LTransient temperature field analysis of a brake in a non-axisymmetricthreedimensional modelM, N. 3aterials Processing Technology, #= )#??# 0$-09.

[0! 5.>ohmann, R.4chiffner, R.8erter, and >.Aeese. L'ontact analysis for drum brakes and diskbrakes using ADI!AM. 5omputers and 4tructures,9#,


10/10


$ol. 3, no. 2, A%rila' 20#! #

[?!4. &ee and T. 'eo. LTemperature and coning analysis of brake rotor using an aisymmetric finiteelement techniqueM, Proc. /th Rorea-Aussia ;nt. 4ymp. 8n 4cience U Technology, $)#??? 9-##.

[!

T. +alvano and R. &ee. LAn analytical method to predict thermal distortion of a brake rotorM, 4BTechnicalPaper, )#??? #???-?-?//0.

[#!T.T.3ackin, 4.5.@oe, R.N.all, .5.edell, *.P.im-3erle, 3.5.ingaman, *.3.omleny,%.N.5hemlir, *..5layton. and >..Bvans, LThermal cracking in disc brakesM. Bng. 7ailurenalysis, =)#??# 2$V92.

[$!Q. Wole(s"a, . *acko, T. Qawistowki, and N. 8sinski. LThermo1&echanical Analysis of Airplane'arbon1'arbon 'omposite $rakes 3sing &"'. &arcM, Warsaw :niversity of Technology, )#??,Paper #??-0

Documents

Disc Brake Assembly