Comparison of Hardness, FRF, Compressibility, and Ultra ... Hardness, FRF... · Pass/Light Truck...

1Copyright © Akebono Brake Corporation. All Rights Reserved.

Scott Severnak, Jill Thomas, Andrew Visser

Comparison of Hardness, FRF, Compressibility, and Ultra-sonic

Modulus Measurements2017 SAE Presentation 17BC-0074

Akebono Brake CorporationFriction Material Design


Friction Quality MeasurementsPass/Light Truck Brake Pad Quality

•There are diverse opinions within the brake community for determining ongoing production quality of a finished brake pad

•This presentation compares several industry methods

•There are two underlying common characteristics assessed across all manufacturers

– Dimensions» Overall thickness, abutment height/length, friction/plate flatness,

parallelism, and topography/shape– Friction Modulus

» All use some type of measurement in attempt to assess raw materials and processing consistency for modulus


Friction Quality MeasurementsMatrix of Main Quality Measurement Types

Compressibility FRF RockwellHardness

Direct Modulus(Ultrasound) Dimensions Comment

Primary Characatersic Desired Modulus Modulus Modulus Modulus Dimensions --

What is it measuring

Approximation of friction modulus and dimensional

effects

Primarily plate modulus &

secondary friction modulus

Friction surface approximation of friction modulus

Approximation of friction modulus

Friction flatness, plate flatness,

parallelism, abutments, etc.

--

Independent instrinsic quality/engineering measurement

of friction materialsNo No Yes Yes Yes

Can one compare quality independent of shape, friction formulation, chamfers/slots etc.?

In Process Correlation No No Poor/Moderate Excellent --Can I determine how a part was processed by correlating to previous process measurements?

Reference SAEJ2468

SAEJ2598

SAEJ2654

SAE Paper2010-01-1701 -- --

Equipment Used for this presentation

Link

1620-H

Zonicbook

618E

Instron Wilson/Rockwell

Series 600

Industrial Measurement

Systems

iETEK

-- --


Friction Quality MeasurementsCompressibility

• Pad compressibility is made up of two primary components

– Friction Modulus» Reciprocal of compressibility without dimensional

influence is an approximate measurement of Young’s modulus.

– Dimensions» Any friction flatness, plate flatness, parallelism, and

topography beyond being “zero” typically contribute to compressibility (i.e. will be part of the deflection in the compressibility). Typical friction flatness, plate flatness, parallelism specifications are in the 100-200 µm (0.10 mm – 0.20 mm) range.


Friction Quality MeasurementsFRF, Hardness, Ultrasound

FRF is made up of two main components but in general is attempting to detect changes in friction modulus

– Pressure Plate (primary)• Material Properties (Modulus)• Plate thickness

– Friction Material (secondary)• Material Properties (Modulus)• Geometric Properties (slots, chamfers, variation within geometric

properties)Rockwell hardness

– Uses a small scale surface approximation of modulus which is then extrapolated to characterize the entire pad

Ultrasound – Yields approximation of modulus based on the fundamental relationship

between the ultrasonic velocity and the material elastic constants


Friction Quality MeasurementsAssessing Friction Modulus

Compressibility FRF Rockwell Hardness Ultrasound

Acquiring Friction

Modulus

Requires machining pads close to ‘zero’ for dimensions

or using small coupon size pieces. Commonly referred to as "Specific" Compressibility

Need to account for other geometric variables (pressure

plate thickness, friction thickness, slot depth, chamfer

size, etc.)

Only rough relationship can be established to modulus Direct measurement

Challenges

Lead time to make parts

Still will have dimensional contributions

Sensitivity to changes to friction modulus lower than

other factors (plate thickness, dimensions)

Have to know relationship to modulus and can be highly

influenced if part is scorched

Hardness measurement on a single pad is highly variable

Newer technology

BenefitsYields combined measurement that gives insites into modulus and fluid displacement

Relatively quick measurement

Can correlate to previous measurements taken in the

process (post hot press, post cure, post grind)

Can correlate to previous measurements taken in the

process (post hot press, post cure, post grind)

ReferenceSAE Presenation BC201-3

SAE Paper 2008-01-2572---- ----- SAE Paper 2010-01-1701


Friction Quality MeasurementsRepeatability/Environmental/Pressure Plate Sensitivity

• N=10 different pad shapes all current OE production• N=9 NAO’s, N=1 Semi-Met• N=6 Akebono, N=4 non Akebono• Measurements:

• Compressibility SAE J2468 T3/100 bar [microns]• FRF SAE J2598 [Hz] (1st bending mode)• Rockwell Hardness SAE J2654 [HRR or HRS]• Ultrasound Modulus [MPa] (note density = 1.00, reference SAE Paper– 2010-01-1701)

• Run 1 - Pads were dried out 2 hours @ 110OC then measured• Run 2 - Pads subjected to 25OC @ 80% RH for 24 hours then measured• Run 3 - Pads were dried out again 2 hours @ 110OC then measured• Run 4 - 0.40 mm ground off pressure plate, dried 2 hours @ 110OC then

measured (simulation of typical min to max plate thickness tolerance and pressure plate flatness almost zero)


3000250020001500

3000

2500

2000

1500

1 - FRF Initial Dry

3 -

FRF

Dry

AkebonoNon Akebono

Friction

FRF - Run 3 vs. Run 1

140120100806040

140

120

100

80

60

40

1 - Comp. Initial Dry

3 -

Com

p. D

ry

AkebonoNon Akebono

Friction

Compressibility - Run 3 vs. Run 1

18001600140012001000800

1800

1600

1400

1200

1000

800

1 - Modulus Initial Dry

3 -

Mod

ulus

Dry

AkebonoNon Akebono

Friction

Modulus - Run 3 vs. Run 1

1009080706050

100

90

80

70

60

50

1 - Hardness Initial Dry

3 -

Har

dnes

s D

ry

AkebonoNon Akebono

Friction

Hardness - Run 3 vs. Run 1

R²=0.99

R²=0.99

R²=1.00

R²=0.81

Friction Quality MeasurementsRepeatability - Run 3 vs. Run 1

• Run 1 - Pads were dried out 2 hours @ 110OC then measured• Run 3 - Pads were dried out again 2 hours @ 110OC then measured

Note: X &Y scales are

same on each respective plot


Friction Quality MeasurementsAbsolute % Change - Repeatability

ModulusHardnessFRFCompressibility

25

20

15

10

5

0

% A

bsol

ute

Chan

ge

1.795390.297067

4.11681

1.79527

% Absolute Change - Repeatability


Friction Quality MeasurementsEnvironmental Sensitivity - Run 2 vs. Run 1• Run 1 - Pads were dried out 2 hours @ 110OC then measured• Run 2 - Pads subjected to 25OC @ 80% RH for 24 hours then measured

Note: X &Y scales are same on each respective plot

3000250020001500

3000

2500

2000

1500

1 - FRF Initial Dry

2 -

FRF

1st H

umid

AkebonoNon Akebono

Friction

FRF - Post Humidity Soak vs. Run 1

1009080706050

100

90

80

70

60

50


2 -

Har

dnes

s 1s

t Hum

id

AkebonoNon Akebono

Friction

Hardness - Post Humidity Soak vs. Run 1

18001600140012001000800

1800

1600

1400

1200

1000

800


2 -

Mod

ulus

1st

Hum

id

AkebonoNon Akebono

Friction

Modulus - Post Humidity Soak vs. Run 1

140120100806040

140

120

100

80

60

40


2 -

Com

p. 1

st H

umid

AkebonoNon Akebono

Friction

Compressibility - Post Humidity Soak vs. Run 1

R²=0.98

R²=0.98

R²=1.00

R²=0.78


Friction Quality MeasurementsAbsolute % Change - Humidity

Modulus - HumidityHardness - HumidityFRF - HumidityComp. - Humidity

25

20

15

10

5

0

% A

bsol

ute

Chan

ge

3.11794

0.752171

5.69179

2.01584

% Absolute Change - Humidity


Friction Quality MeasurementsPressure Plate Thickness/Flatness Sensitivity - Run 4 vs. Run 1

3000250020001500

3000

2500

2000

1500

1 - FRF Initial Dry

4 -

FRF

Plat

e G

ri nd

(Dry

)

AkebonoNon Akebono

Friction

FRF - Post Plate Grind vs. Run 1

• Run 1 - Pads were dried out 2 hours @ 110OC then measured• Run 4 - 0.40 mm ground off pressure plate, dried 2 hours @ 110OC then measured

140120100806040

140

120

100

80

60

40


4 -

Com

p. P

late

Grin

d (D

ry)

AkebonoNon Akebono

Friction

Compressibility - Post Plate Grind vs. Run 1

18001600140012001000800

1800

1600

1400

1200

1000

800


4 -

Mod

ulus

Pla

te G

rind

(Dry

)

AkebonoNon Akebono

Friction

Modulus - Post Plate Grind vs. Run 1

1009080706050

100

90

80

70

60

50


4 -

Har

dnes

s Pl

ate

Grin

d (D

ry)

AkebonoNon Akebono

Friction

Hardness - Post Plate Grind vs. Run 1

R²=0.87

R²=0.96

R²=0.997

R²=0.84



Friction Quality MeasurementsAbsolute % Change – Pressure Plate Thickness Sensitivity

Modulus - PlateHardness - PlateFRF - PlateComp. - Plate

25

20

15

10

5

0

% A

bsol

ute

Chan

ge

9.8989

3.550884.88762 5.20253

% Absolute Change - Plate


Friction Quality MeasurementsWith “Use” Sensitivity

• N=4 vehicle platforms• All NAO materials• Various typical OE dynamometer development tests conducted

(Performance, FMVSS, Noise, Wear, Thermal Abuse etc.)• Measurements of Compressibility, FRF, Hardness, Modulus conducted pre

and post test • Compressibility SAE J2468 T3/100 bar [microns]• FRF SAE J2598 [Hz] (1st bending mode)• Rockwell Hardness SAE J2654 [HRR or HRS]• Ultrasound Modulus [MPa] (note actual density used, reference SAE

Paper 2010-01-1701)

•Can one assess a field returned part for it’s initial quality metric?


Friction Quality MeasurementsPost Dynamometer Test vs. Initial Measurements

320030002800260024002200200018001600

3200

3000

2800

2600

2400

2200

2000

1800

1600

Pre FRF

Post

FRF

ABCD

Platform.

FRF - Post Test vs. Pre Test

140120100806040

140

120

100

80

60

40

Pre Comp

Post

Com

p

ABCD

Platform.

Compressibility - Post Test vs. Pre Test

1007550250

100

75

50

25

0

Pre Hardness

Post

Har

dnes

s

ABCD

Platform.

Hardness - Post Test vs. Pre Test

40003500300025002000

4000

3500

3000

2500

2000

Pre Modulus

Post

Mod

ulus

ABCD

Platform.

Modulus - Post Test vs. Pre Test

R²=0.56 R²=0.99

R²=0.00 R²=0.80



Friction Quality MeasurementsAbsolute % Change – Post Dynamometer vs Initial

ModulusHardnessFRFCompressibility

100

90

80

70

60

50

40

30

20

10

0

% A

bsol

ute

Chan

ge

13.5202

2.26982

16.0978

5.80811

% Absolute Change vs. Measurement Type


Friction Quality MeasurementsDetecting Small Changes Raw Material Properties

•Study was conducted to assess measurement types ability to discriminate between small changes in raw material physical properties• Passenger car NAO• A baseline mix and derivatives were made by replacing 1 raw material at a

time• The replacement raw material only differed by a small change in physical

properties

• Measurements conducted on finished pad assemblies• Compressibility T3/100 bar [microns]• FRF [Hz] (1st bending mode)• Rockwell Hardness [HRR or HRS]• Ultrasound Modulus [MPa] (note actual density used, reference SAE

Paper 2010-01-1701)

•



7 - Ino

rganic

Fiber

6 - Abra

sive

5 - Fil

ler

4 - In

organ

ic Fib

er

3 - Fil

ler

2 - Ino

rganic

Fiber

1 - Base

line

180

170

160

150

140

130

Raw Material

Com

pres

sibi

lity

[um

]

152.33149.335

156.78157.035154.984153.14

159.97

Interval Plot of Compressibility [um]95% CI for the Mean

Individual standard deviations are used to calculate the intervals.

Statistically different mean

(95% Confidence)



7 - In

organic

Fiber

6 - Abras

ive

5 - Fil

ler

4 - In

organ

ic Fib

er

3 - Fil

ler

2 - In

organ

ic Fib

er

1 - Ba

seline

2940

2920

2900

2880

2860

2840

Raw Material

FRF

[Hz]

2871.46

2887.662877.192880.512877.612878.692876.53

Interval Plot of FRF [Hz]95% CI for the Mean


No statistical difference in means



7 - In

organ

ic Fib

er

6 - Abra

sive

5 - Fi l

ler

4 - In

organ

ic Fib

er

3 - Fil

ler

2 - In

organic

Fiber

1 - Ba

seline

90

85

80

75

70

Raw Material

Fini

shed

Har

dnes

s [H

RR]

82.154882.612581.662581.587580.9

82.437581.25

Interval Plot of Finished Hardness [HRR]95% CI for the Mean


No statistical difference in means



7 - In

organic

Fiber

6 - Abras

ive

5 - Fil

ler

4 - In

organ

ic Fib

er

3 - Fil

ler

2 - In

organ

ic Fib

er

1 - Ba

seline

2400

2200

2000

Raw Material

Fini

shed

Mod

ulus

[MPa

]

2190.592203.532154.282149.022160.42

2202.68

2131.54

Interval Plot of Finished Modulus [MPa]95% CI for the Mean


Statistically different mean

(95% Confidence)



290028752850 858075 240022002000174

162

150

2900

2875

2850

85

80

75

Compressibility [um]

FRF [Hz]

Finished Hardness [HRR]

Finished Modulus [MPa]

Correlation Between Measurements

R²=0.25

R²=0.56

R²=0.06

R²=0.09

R²=0.13 R²=0.09


Friction Quality MeasurementsSummary Matrix

• Compressibility FRF RockwellHardness

Direct Modulus(Ultrasound)

Repeatability 1.80% 0.30% 4.11% 1.80%

Sensitivity to Humidity 3.11% 0.75% 5.69% 2.02%

Sensitivity to Plate Tolerance/Plate Flatness 9.90% 3.55% 4.89% 5.20%

Changes "with use" 13.52% 2.27% 16.10% 5.81%

Sensitivity to friction modulus Excellent w/o dimensional component Poor Poor Excellent

Independent instrinsic quality/engineering measurement

No(shape dependent)

No(shape dependent) Yes Yes

In Process Correlation No No Poor/Moderate Excellent

• Direct modulus measurements on finished brake pad needs a formal testing procedure

• Direct modulus on finished brake pads should be considered as a primary assessment of friction quality along with dimensional measurements


Friction Quality MeasurementsAcknowledgments

- Friction Team at Akebono Engineering Center- Friction Team at Akebono Brake Glasgow


Friction Quality MeasurementsEnd

Thank you

– Scott Severnak– Akebono Brake Corporation– 34385 West Twelve Mile Road, Farmington

Hills MI. 48390 – 248-489-7484– [email protected]

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