Conclusions Morphology differences - correlation for the last contact phase

Thermo-mechanical and tribological analysis of pad-disc contact in a braking tribometer

david.tumbajoy-spinel@insa-lyon.fr yannick.desplanques@centralelille.fr

anne-lise.cristol@centralelille.fr yves.berthier@insa-lyon.fr

sylvie.descartes@insa-lyon.fr

Mechanical features

Surface evolution after contact: common aspects for both case scenarios

Introduction

Contacts

Heat evolution: pad measurements

D. Tumbajoy-Spinel1, Y. Desplanques2, A. L. Cristol2, A. Beaurain2, Y. Berthier1, S. Descartes1

1. Univ Lyon, CNRS, INSA-Lyon, UMR5259 – LaMCoS, F-69621 Villeurbanne, France 2. Univ Lille, CNRS, Centrale Lille, FRE 3723 – LML, F-59000 Lille, France

Test 1 Test 2

Short cooling period between tests

Pad

Disc

TDo

T [ºC]

t [s]Test 3 Test 4

WITH CUMULATIVE HEAT

Test 1 Test 2

Cooling until initial disc temperature threshold (TDo)

Pad

Disc

TDo

T [ºC]

t [s]

WITHOUT CUMULATIVE HEAT

50 mm

The main issue of this work is to understand the material behavior in a disc-pad interaction under similar mechanical conditions but different thermal backward histories. In this project, experimental tests are performed in a braking tribometer set-up [1] using a steel disc (C45) and a metallic composite pad (70 % matrix Fe/Cu, 20 % graphite and 10 % ceramics SiC/ZrSiO4) [2]. Two different sequences are carried out using slowdown braking tests: (i) without and (ii) with cumulative heat. At the end of each cycle, a hold-braking test is done to restore the pad surface for both case scenarios. The surface tribological evolutions are correlated with the thermo-mechanical measurements. A comparison between both cases (i, ii) is carried out as well.

Pad temperatures are measured by thermocouples at 2 mm from the near-surface. This data permits to point out a contour map of pad temperature gradients. Despite of the thermal fluctuations, the global mechanical conditions remain the same for both cases (mean friction coefficient of 0.4).

Braking test sequences are composed by 5 main phases:

Specific braking test sequences were developed in order to produce fairly recurrent mechanical states and to compare two different thermal backward histories for the same disc-pad contact.

During the phase #3 (Tests), the temperature gradient reveals some contact alternation between the external regions and the central region of the pad. The IR thermography of the disc reveals that the contact starts in the outer radius and it migrates to the inner regions.

For the phase #5 (hold-braking), the thermal gradient shows that the mechanical contact settle on the external radius of the pad.

Effect of local temperature: The surface of the pad evolves differently according to the local temperature level at each region. Homogeneous 3rd body plateaus appear in zones of higher temperatures (higher power dissipation) for the last mechanical phase: hold-braking. Third body morphologies: third body in the case of “cumulative heat” sequence is compacted and fully mixed, while it is powdery in the case of “without cumulative heat” sequence.

Δr

[m

m]

θ [deg] InOut

Int

Ext

TEST 17 – WITH cumulative heat Temp.

Δr

[m

m]

θ [deg] InOut

Int

Ext

TEST 3 – WITH cumulative heat Temp.

1 2 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 1911 20

TP1 XTP4 XTP7 X

Inner radius – 20 tests WITHOUT cumulative heat

Inner radius – 20 tests WITH cumulative heat

1 2 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 1911 20

Δr

[m

m]

θ [deg] InOut

Int

Ext

TEST 6 – WITHOUT cumulative heat Temp.

Δr

[m

m]

θ [deg] InOut

Int

Ext

Temp.TEST 7 – WITHOUT cumulative heat

TEST 6 TEST 7

TEST 3

TEST 17

TP7 = Tmax = 340 ºC TP4 = Tmax = 350 ºC

TP4 = Tmax = 600 ºCTP7 = Tmax = 430 ºC

Surf

ace

p

rep

arat

ion

TEST

Surf

ace

Res

tora

tio

n

1 2 43

5

Scenario 1WITHOUT

cumulativeheat

Scenario 2WITH

Cumulativeheat

T9

T8

T7

T11

T6

T5

T4

T10 T3

T2

T1

V

Sortie Entrée

θ40º

0º20º

r

ωdisc

In

PAD

Out

1000 µm

1000 µm

1000 μm

1000 μm

1000 μm

Before contact

Without cumulative heat

With cumulative heat

Sliding direction

Sliding direction

Sliding direction

3rd body(powder)

SiC

ZrSiO4

500 μm

SEM (BSE)

Graphite

Metallic matrix(Cu/Sn, Fe)

Sens du contact500 μm

3rd body -spread layer (mainly Fe, O)

3rd body - powder(mainly Fe, O)

IR Thermography of the disc

References:

……

500

1000

1500

2000

ω [rpm]

t [s]

Running-in Pre-TESTS

20 TESTS

HOLDPost-TESTS

Scenario 1 : without C. H.Scenario 2 : with C. H.1 2 4

3

5

TEST

3

Disc

Pad

ω

T

Ft

Fn

Loading Force

Phase 1. Running-in 2. Pre-TESTS 3. TESTS 4. Post-TESTS 5. Hold

Brakings (amount) 40 5 20 5 1

ωo [rpm] 1000 800 1700 800 500

ωf [rpm] 300 300 300 300 500

Inertia [kgm²] 5 10 10 10 ---

Fn [N] 1000 1000 1000 1000 1000

Dissipated Energy [kJ] 24.9 30.2 153.5 30.2 ---

Δr

[m

m]

θ [deg] InOut

Int

Ext

HOLD – WITH cumulative heat Temp.

Δr

[m

m]

θ [deg] InOut

Int

Ext

HOLD – WITHOUT cumulative heat Temp.

Tmax

Tmax

500 μm

TP9 = 170 ºC

500 μm

TP7 = 210 ºC

500 μm

TP1 = 150 ºC

500 μm

TP3 = 290 ºC

Patchy 3rd body

Powdery 3rd body

Compacted fully mixed 3rd body

Compacted patchy 3rd body

[1] Y. Desplanques, O. Roussette, G. Degallaix, R. Copin, Y. Berthier, Wear, Vol. 262, p. 582-591, 2007. [2] R. Mann, V. Magnier, J.F. Brunel, F. Brunel, P. Dufrénoy, M. Henrion, Wear, Vol. 386-387, p. 1-16, 2017.

Acknowledgement This work is supported by the French National Research Agency (ANR-12-VPTT-0006 CoMatCo). The authors would like to thank the

academic and industrial partnership with Sapienza University, Flertex Sinter and Chassis Brakes International.

500 μm10 μm 30 μm

200 μm 5 μm 5 μm

Sliding direction

Thin layer of 3rd body formed by powder agglomeration

3rd bodyplateaus

Internal flow of 3rd body

Fine layer of spread 3rd body powdercovering other

composite elements (graphite,

metallic matrix, ceramics)

3rd body powder is spread by

compacting and shearing, leading a

layer of piled up thin “Stratums”

3rd body particle size

gradient

SiC particles fragmentation

Lamellar morphology

Graphite

A

A B

B

C

C D E

D

E

Trapped 3rd body powder filling

surface valleys and hollows

C

O

Fe

Cu

Si Zr

Fe

Fe Cu0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 1 2 3 4 5 6 7 8 9 10

Co

un

t

keV

Co

un

t

EDX – ZrSiO4

keV C

O

Fe

Cu Si Mn

Fe

Fe Cu0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 1 2 3 4 5 6 7 8 9 10

Co

un

t

keV

Co

un

t

EDX - 3rd body

keV