SIMULATION OF ON-HIGHWAY FATIGUE TEST ( CHUCKER ) FOR · PDF file1 simulation of on-highway fatigue test ( chucker ) for the heavy vehicle brakes by using fea method by s. hilda pektas

1

SIMULATION OF ON-HIGHWAY FATIGUE TEST

( CHUCKER ) FOR THE HEAVY VEHICLE

BRAKES BY USING FEA METHOD

by

S. Hilda PEKTAS

November, 2006

IZMIR

SIMULATION OF ON-HIGWAY FATIGUE TEST ( CHUCKER )

FOR THE HEAVY VEHICLE BRAKES BY USING FEA METHOD

ABSTRACT

The aim of this study is to carry a long-term test into computer environment where it

will take just a few day by using finite element method to solve. As being usual in

designing, the results of the test are used in re-design the components or acceptance of the

parts coming from the new suppliers for supplier changes.

The brakes of a heavy vehicle run into serial experiments to see its validity according

to customer conditions. The most important and the longest one of those tests, Brake

Components On-Highway Fatigue Test: Chucker Test, was chosen as a model for

simulation. The test is done under similar conditions very close to real one to see the

deformation on brake components after a few hundred thousand of cycles where one cycle

is simply described such as braking and releasing the brake in certain of time.

During the thesis, firstly the working principle of air wedge brake was studied to find

the maximum forces acting on the components to use them as boundary conditions in the

following section. Then the model of brake was made on Ansys WB 9.0 and found the

most critical areas in respect of its stress distribution. According to this data and by the

lead of past experiences, the strain gages were sticked and the test run. The data was

recorded just to observe the changes in gages at any cycle during the test as elongation and

converted to stress at the end of experiment to compare the results with the model.

Key words: brake, fatigue, heavy vehicle, Ansys, cycle.

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FREN MEKAN�ZMASI YORULMA TEST�N�N FEA METODUYLA

S�MULASYONU

ÖZ

Çalı�manın amacı, sonuçlanması birkaç ay süren bir testi bilgisayar ortamında simüle

ederek birkaç gün gibi kısa bir sürede sonuca gidebilmektir. Birçok tasarımda da oldu�u

gibi bu test sonuçları, ürünü olu�turan alt parçalar yeniden tasarlanırken veya tedarikçi

de�i�ikliklerinde parça uygunlukları belirlenirken esas girdileri olu�turacaklardır.

A�ır vasıta frenlerinin, mü�teri tarafından tayin edilen kullanım �artlarına uygunlu�unu

onaylamak için bir seri test yapılmaktadır ve bunlardan en önemli ve uzun süreli olanı bu

çalı�mada simüle edilmeye çalı�ılan test olmu�tur ki literatürde A�ır Vasıta Frenlerinin Yol

�artlarında Yorulma Testi: Chucker Test olarak bilinir. Test, aracın çalı�ma ko�ullarındaki

frenleme biçimini yansıtan �artlar altında yüz binlerce kez frenleme yapılıp frenlerdeki

deformasyonun belirlenmesi amacını ta�ımaktadır.

Çalı�ma boyunca öncelikle havalı bir frenin çalı�ma prensibi incelenerek maksimum

kuvvet de�erleri belirlenmi� ardından bu veriler sınır �artı kabul edilerek Ansys WB 9.0 da

fren modeli olu�turulmu�tur. Geçmi� tecrübelerden ve fren modelinden elde edilen

sonuçlarla test düzene�i üzerindeki frenin en riskli noktaları belirlenerek o noktalara strain

gageler yapı�tırılmı� ve test ekipmanı çalı�tırılmı�tır. Strain gagelerdeki istikrarı

gözlemleyebilmek adına belirli döngülerde veriler alınmı� ve hedef döngüye ula�ıldıktan

sonra testen elde edilen uzama verileri gerilim de�erine çevrilerek modeldeki de�erlerle

kar�ıla�tırılmı�tır.

Anahtar sözcükler : Fren, yorulma, a�ır vasıta, Ansys, döngü.

1. Introduction

Even the simplest stress analysis of a product that occurs from combination of more

than twenty component working to each other dependently, is rarely complex a test of an

air brake for heavy vehicles was tried to done on computer and the steps of this effort can

be witnessed at the following sections.

2. Stopping : As a Matter of Action

A vehicle in motion may be though as a point mass in its center of gravity and the

motion shows that it has a kinetic energy. Stopping is the change of this kinetic energy into

another form of energy by creating an opposite force in the direction of motion. The

simplest way of creation of this opposite force can be done by using friction. Due to that all

kind of brakes with a few exceptions work with using this method for years.

2.1 The Principle of Friction

The friction that has tried to be minimized nearly all engineering problems, forms the

base of working principle of a brake. The kinetic energy of the vehicles turns to thermal

energy by rubbing two main components called pad and disk for disk brakes and called

lining and drum for the drum brakes. These two combination can be seen in Figure 2.1.

Fig. 2.1 a) A simple drum brake showing the lining and its drum (Meritor RD410 / Egefren )

b) Air type disk brake with pads and caliper ( Meritor ELSA225 / Egefren )

2.2 The Inner Parts Of A Wedge Type Air Drum Brake

The most important parts are shown in the following figures, Figure 2.2 and 2.3,

while translating the force. Stopping will occur because of friction between lining and

drum where the drum is turning with the effect of tires while the brake so the lining is

stationary. The rest of the inner parts just help to supply a touch between these two

components when the driver push the brake pedal. That is, air chamber diaphram, wedge,

roller, anchor plunger and shoe assembly move forward to close the gap between the

linings and drum when the brake pedal is pushed and the shoe return spring is used to cut

this contact when it is released. In Figure 2.3, the transmission of this force is shown.

Fig. 2.2 The inner parts of Meritor–RD410 brake (Meritor-Egefren Service Booklet )

Fig. 2.3 Force transmission of brake ( Meritor -Egefren Service Booklet )

2.3 The Calculation Of The Brake Force

Air Chamber :

F1 = p1 x A1 ............................................ ( eq.1 )

At the full braking:

1. Pressure on air chamber diaphram (p1 ) : 7.5 bar

2. Area for T12 Air chamber ( A1 ) : 12 inch2

So;

F1 = 7.5 x 12 x (2.542 x 9.81) = 5700 N

Wedge :

�Fx = 0 ; F1 = 2 x F2 x sin (6°) ................... ( eq. 2 )

For F1 = 5700 N;

F2 = 5700 / (2 x sin ( 6°) ) = 27265.4 N

Roller :

Anchor Plunger:

�Fy = 0 ; F3 x cos (12°) = F2 x cos (6°) ....................... ( eq. 3 )

For F2 = 27265.4 N;

F3 = F2 x cos (6°) / cos (12°) = 27721.8 N

Adjustable Screw Assy :

�Fy = 0 ; F2 x cos ( 6°) = F4 ............................................... ( eq. 4 )

For F2 = 27,265.4 N;

F4 = F2 x cos (6°) = 27,116.4 N

Lining Shoe Assy :

Drum

��Fy = 0 ; F3 x cos ( 12°) + F4 = ��

dbp **cos*3/2

0� ................... ( eq. 5 )

��M = F4 x L – L x ��

dbp **cos*3/2

0� ......... (eq. 6 )

For F3 = 27,721.8 N and F4 = 27,116.4 N;

M = 40,000 Nm

3. Maximum Stress Value on Brake

When the force F2 found in previous section was applied to the anchor plungers of the

model of wedge brake RD410 the results can be shown in Figure 3.1. Here the model has

approximately 150,000 nodes and the contact between drum and lining has chosen

frictional type with the coefficient of 0.36. The other contacts between the inner parts were

chosen as frictionless due to the usage of grease. The area colored orange in figure 3.1

shows the most critical locations on brake under these boundary conditions.

Fig. 3.1 Ansys analysis of RD410 Wedge Type Brake

In previous section, the other forces acting on inner parts were calculated. They were

calculated to show how a brake works and also, to have some datas to check the validity of

brake model or to see the whole brake model is under control. The method for self-control

is;

1- Select any part to apply the related forces on its model and apply the conditions

2- Run the part model in Ansys and get the results

3- Take a section in the model of brake that includes the details of selected part

stress analysis results

4- Compare the both stress values. If they are close to each other then one can say

that the applied conditions and some assumptions done for the model and parts

are valid.

The anchor plunger was chosen for this control method and the stress values can be

seen in figure 3.2 and 3.3.

Fig. 3.2 The forces that act on anchor plunger alone and its stress analysis

Fig. 3.3. The value of stress analysis of anchor plunger while working in brake assembly.

4. Test Equipment and Its Working Principle

The aim of the test is to investigate the deformation of a brake in any step of regular

usage. A real couple of brake and drum works at its real condition except the high speed

and temperature. However, the torque is always applied at its maximum in forward

direction. In figure 4.1 some photos of the test equipment was shown.

Fig. 4.1 Shown test equipment while it is working

The procedure of test may be divided into two. First is forward direction of the piston

that turns the drum in clockwise direction. This step takes nearly 3 seconds while braking

at maximum torque first 1 second and then decreasing in torque to 30% of its maximum.

Following 1 second passes with this less torque. After 3 seconds, whole system stops and

drum starts to turn in counter-clockwise direction. Then braking starts with torque of 30%

of its maxium. During 3 seconds the braking occurs and then whole system stops again.

Apropriate Wheel Ends

Cylinder and Torquemeter

Hydrolic Power Unit

Brake Assy

Electronic

Computer for datas

Hydrolic Power Unit Hydrolic Power Unit Hydrolic Power Unit

This movement calls as one cycle. The procedure can be shown in Figure 4.2

schematically.

Fig. 4.2 Torque vs. Time diagram of chucker test ( Meritor Test Manuel – TP255 )

5. Measurement Of The Test Results

In previous section one cycle is described. According to customer need, the neccessary

amount of cycle applies on brake and then visual investigation procedure starts. During

investigation some photos are taken that shows the deformation clearly. For a purpose as

modeling a test with finite element method, however, the visual results cannot be

reasonable. So, strain gages were used in critical points to measure the amount of

deformation. The areas are shown on Figure 5.1.

Fig. 5.1. Areas where the strain gages were sticked

The strain results taken during the test in different cycles are shown in Table 5.1.

There is no any value for Gage 6 because after 50,000 cycles the gage was out of order.

Table 5.1 The values read from gages directly

Tablo 5.2 The differences of gage values according to referance value

The values of gages were used to calculate the stress values at the critical points.

While chosing the direction of gages to stick the stress distribution was concerned. For

example, if the force in y direction is much higher than the x direction at that point the

stress occurance in x direction neglected and a longutational gage sticked in the y direction

only. Similarly, the mathematical calculation of stress is done by the same way. While

finding the stress value, strain values multipled with modulus of elasticity.

Below, these calculations were done and compared with the results of brake model

done in Ansys.

Gage 1 :

Analytic Calculation :

�� = E * �� = 170 * 103 * 774 *10-6 = 131,58 MPa

Result from finite element analysis : 7,7 MPa

Fig. 5.2 ANSYS analysis result

Gage 2 için :


�� = E * �� = 170 * 103 * 528 *10-6 = 89,76 MPa



Gage 3 için :


�� = E * �� = 170 * 103 * 647 *10-6 = 109,99 MPa



Gage 4 için :


�� = E * �� = 170 * 103 * -64 *10-6 = - 10,88 MPa



Gage 5 için :


�� = E * �� = 170 * 103 * 286 *10-6 = 48,62 MPa



Gage 6 için :


�� = E * �� = hesaplama dı�ı

Result from finite element analysis : -35,28 MPa


Gage 7 için :


�� = E * �� = 170 * 103 * -203 *10-6 = - 34,51 MPa

Result from finite element analysis : - 81,12 MPa


Gage 8 için :


�� = E * �� = 170 * 103 * -248 *10-6 = - 42,16 MPa

Result from finite element analysis : -18,25 MPa


Gage 9 için :


�� = E * �� = 170 * 103 * -135 *10-6 = - 22,95 MPa

Result from finite element analysis : - 42,61 MPa


Gage 10 için :


�� = E * �� = 170 * 103 * 701 *10-6 = 119,17 MPa


�� Fig. 5.11 ANSYS analysis result��

6. In Conclusion

The results in previous section is the summary of this work. When compared, the

results don’t look like too different than expected except for Gage1 and Gage4. The finite

element result for Gage1 seems more applicable than the test results. Because in the

longitutional directional stress must be much less than value in horizantal direction that

seen in Gage2. However, the value for Gage4 must be compresion and also, must be close

to the values in Gage9 because they are both identical about the area where sticked.

To sum up, the model cannot reflect the test exactly but it converges. However, the

both results can be closer if the assumptions while modelling converges the reality more.

For example, using much more nodes, frictional contacts, adding tempurature effect,

adding some impurities in critical ares etc. Morever, more test must be done to reach

accurate analytical results.

REFERANCES

Aksoy, T. (1984). Kırılma Mekani�i. �zmir: Dokuz Eylül Uni. MM Fak. Mak. Muh. Bol.

Aksoy, T. & Onel, K. (1990). Malzeme Bilgisi-1. (3rd ed.) Izmir: Dokuz Eylul Uni. MM

Fak. MM/MAK-90 ey 086

Arvin Meritor Stopmaster Brakes Handbook ( n.d. )

Day A. J. ve Shilton B. R., (2005). Braking Of Road Vehicles. University of Bradford.

Egefren Stopmaster Brakes Handbook ( n.d. )

Ereke M, Göktan A.G. & Güney A. (1995). Ta�ıt Frenleri. Turkiye: Alliedsignal

Automotive .

Limpert, R. (1999). Brake Design and Safety (2nd ed.). SAE International

Unlu, B. S. ( 2005 ). Bazı Metal Malzemelerin Yorulma Dayanımlarının Belirlenmesi.

C. B. U. Muh. Fak. Makina Muh. Bol. Metal Makina [SAYI 156]

Documents

SIMULATION OF ON-HIGHWAY FATIGUE TEST ( CHUCKER ) FOR · PDF file1 simulation of on-highway fatigue test ( chucker ) for the heavy vehicle brakes by using fea method by s. hilda pektas