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Benchtop Brake Material Screening:
Can we correlate with full scale AK Master?
Patrick Markus,Bruker Nano Surfaces
Tribology Days 2017, Vattenfall, Älvkarleby
This is why we all need good brakes ……
2
Bruker Confidential 3
The standard in predicting vehicle stopping
performance is a full-scale Dynamometer test
– COF can be measured under a given set of
conditions
– This information is key in evaluating brake pad
materials
– Equipment and tests are expensive and time-
consuming
– Protocol follows AK Master (SAE J2522)
standards
Development phase before release
Bruker Confidential 4
Dynamometer output data
Bruker Confidential 5
A benchtop developmentUMT Tribolab - Brake Material Tester
Collaboration with Greening Inc, ITT and Southern Illionois University
Bruker Confidential
Replicating the Dyno Conditions
6
5 Key Tribology-elements:
• Materials
• Contact Geometry
• Loading
• Motion
• Environment
UMT Tribolab - Brake Material Tester
Bruker Confidential
• Use same Materials as used in Dyno Test
7
1. Materials
Bruker Confidential 8
Minimum Contact Size due to Non Homogenous Nature of Material
0.5 mm
Choose button sample size to be 25x
larger than area shown in this image, to
capture inhomogeneous mixture
Use three buttons from each pad
to further get “average”
representation of material
<- Finish rotor to 320 grit, as in Dyno testing
2. Contact Geometry
Bruker Confidential 9
• Calculate same contact stress on pads as from Dyno, by
using:
• Hydraulic line pressure = most sequences run at 3 MPa
• Piston size (48 mm diameter), and
• Pad area (~ 300 mm2)
• Gives 1MPa contact pressure
• With the UMT TriboLab sample dimensions: 1 MPa = 380 N
3. Loading
Bruker Confidential
Need to replicate car brake pad sliding speed on UMT TL test pads
Wheel
Diameter
Rotor Effective
Radius
UMT
radius
4. Motion - Velocity
Vehicle velocity (km/h)
π x tire diameter (m/rev) Wheel rpm = x (103 m/km) x (h/60 min)
Wheel rpm x π x rotor diameter (m/rev) x (min/60 sec)Sliding Velocity
at Brake Rotor
(m/sec)
= =
Sliding Velocity
at button sample
(m/sec)
sliding velocity at button (m/sec)
π x button path diameter (m/rev) UMT rpm = x (60 sec/min)
Bruker Confidential 11
• Provide artificial “deceleration” based on that from Dyno
tests
• Benchtop test has no inertial flywheels, only drive motor, so a
full brake application would stop test immediately
• Calculate stopping time (or time to final, lower velocity in
snub tests) from deceleration and initial velocity
• Program this deceleration into benchtop tester
• Example: Dynamometer simulating a vehicle stop of:
• 120 km/hr -> 40 km/hr @ 0.4g decel
• Sliding speed of 15.6 m/s -> 5.25 m/s
• Assume constant deceleration
• Time required: 5.7 seconds
4. motion c’td – Velocity Profile
Bruker Confidential 12
• Dry, Humidity
• Temperature of pad measured
• Temperature of rotor measured
• Test initiation dictated by rotor temperature
• Test sequences 6.3, 6.4, 6.5 and 6.8 are all
conducted using Initial Braking Temperature (IBT) of
100 C or less
• Benchtop tester programmed to begin each
measurement in these sequences with IBT < 100 C
5. Environment
Bruker Confidential 13
How does it look like and what do you get …
0 2 4 6 8 10 12 140
100
200
300
400
500F
z: F
orc
e (
N)
Fz
V
Tpad
Trotor
Tz0
500
1000
1500
2000
2500
Deceleration
V: S
pee
d (
rpm
)
0
20
40
60
80
100
120
140
Tpad (
°C)
0
20
40
60
80
100
120
140
Tro
tor (°
C)
0
2
4
6
Tz: T
orq
ue
(N
*m)
Varying the speed from 2089 to 787 rpm (80-30 km/h) in 5.5
s, under an applied force of 300N (0.75 MPa contact
pressure). Force and speed are controlled, while torque and
temperatures are monitored. Typically, torque increases
while speed is reduced at constant contact pressure
Bruker Confidential 14
UMT TriboLAB - Brake Material Tester
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Co
eff
icie
nt o
f F
rictio
n
0
50
100
150
200
250
300
350
400
Ro
tor
Tem
pe
ratu
re (
°C)
1 2 3 4 5 6
Dynamometer
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Co
eff
icie
nt o
f F
rictio
n0
50
100
150
200
250
300
350
400
Ro
tor
Tem
pe
ratu
re (
°C)
1 2 3 4 5 6
UMT-TL
The data collected during the tests show good correlation between the full-scale and the
benchtop tests, not only from the calculated average coefficient of friction (CoF), but also
in the behavior of the torque that has similar trend and shape.
CoF
Bruker Confidential 15
UMT TriboLAB - Brake Material Tester
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Coe
ffic
ient of F
riction
0
50
100
150
200
250
300
350
400
Roto
r T
em
pera
ture
(°C
)
0.3
3
0.6
6
0.9
9
1.3
2
1.6
5
1.9
8
2.3
1
2.6
4
Contact Pressure [MPa]
Dynamometer
0.0
0.1
0.2
0.3
0.4
0.5
0.6
300
0 k
Pa
flu
id
200
0 k
Pa
flu
id
Coe
ffic
ient of F
riction
400
0 k
Pa
flu
id
* * *
0
50
100
150
200
250
300
350
400
Roto
r T
em
pera
ture
(°C
)
0.3
9
0.5
2
0.6
5
0.7
8
0.9
1
1.0
4
1.1
7
1.3
0
Contact Pressure [MPa]
UMT-TL
Contact Pressure
shows step 6.4.2 aimed to measure the sensitivity to applied brake pressure when
testing the system at snubs of 80-40kmh
Bruker Confidential 16
UMT Tribolab - Brake Material Tester
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Coeffic
ient of F
riction
0
50
100
150
200
250
300
Roto
r T
em
pe
ratu
re (
°C)
1 2 3 4 5 6
Dynamometer
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Coeffic
ient of F
riction
0
50
100
150
200
250
300
Roto
r T
em
pe
ratu
re (
°C)
1 2 3 4 5 6
UMT-TL
CoF Cold Application
Good correlation between dyno and UMT-TL results testing materials at 40°C (“Cold
Application”, step 6.6), the values of CoF were very close
Bruker Confidential 17
UMT Tribolab - Brake Material Tester
0.0
0.1
0.2
0.3
0.4
0.5Rec. 1 (µF1)
Fade 1 (µF1)
Cold (µT40)
Char. 2 (µ0P61)
µ120 120-80
80-40
40-5
Char. 1 (µ0P61)
Burnish 1
Green µ
Dynamometer Material A
UMT Material A
Most of the values are within 10% difference – Good correlation according to industry experts
Comparison in the CoF for each step
Bruker Confidential
Can UMT-Tribolab do more then only brakes?
18
Bruker Confidential 19
UMT-Tribolab Lower Drive Types
Linear & Reciprocating Drives
Max. Stroke 25 mm
Min. Stroke 0.1 mm
Position resolution 1µm
Speed 0.1 to 60 Hz
Max. Load 2,000 N
Stroke vs Frequency60 Hz @ 2 mm
20 Hz @ 25 mm
Reciprocating Drive Technical Specifications
Bruker Confidential 20
UMT-Tribolab Lower Drive Types
Rotary & Block-on-Ring Drives
Speed 0.1 to 5,000 rpm
Max. Torque >5 Nm @ 100 rpm, 2.5 Nm @ 5,000 rpm
Max. Load 2,000 N
Rotary Drive Technical Specifications
Speed 0.1 to 5,000 rpm
Max. Torque >5 Nm @ 100 rpm, 2.5 Nm @ 5,000 rpm
Max. Load 2,000 N
Block-on-Ring Drive Technical Specifications
Bruker Confidential
UMT-Tribolab Force Sensors
21
Fz
Fx
SPECS\MODEL FVL-G FL-G DFM-0.5-G DFM-1-G DFM-2-G DFH-5-G DFH-10-G DFH-20-G DFH-50-G DFH-100-G DFH-200-G
Low 1mN 5mN 0.05N 0.1N 0.2N 0.5N 1N 2N 5N 10N 20N
High 100mN 500mN 5N 10N 20N 50N 100N 200N 500N 1,000N 2,000N
Resolution 10µN 50µN 0.25mN 0.5mN 1mN 2.5mN 5mN 10mN 25mN 50mN 100mN
FL series DFM series DFH series
Bruker Confidential 22
Wide Range of Advanced Sensors for Environmental
and Test Characterization
• Advanced Sensors are field-installable, and easy to configure to add increased test characterization and accuracy of the UMT-Tribolab system.
• Advanced Sensors available include:
• Acoustic Emission
• Electrical Contact Resistance
• Temperature
• Humidity
• Micro-Wear, Deformation
Acoustic Emission Sensor Used to Detect Coating Delamination
Bruker Confidential
UMT-Tribolab Product Selector Guide
Main Unit and Lower Drive Accessories
L-DRIVE
23
ROT-DRIVE
ROT-400
ROT-1000
ROT-HUMID/COOL
REC-350
REC-1000
REC-HUMID/COOL
REC-DRIVEBOR-DRIVE
BOR-150
April 11-13, 2017 24Bruker Confidential18. Dezember 2017 24© Copyright Bruker Corporation. All rights reserved