bruker-slidingfriction-presentation-07262013.pdf

8/14/2019 Bruker-SlidingFriction-presentation-07262013.pdf

1/44

1

The Connection between Surface Texture and Sliding Frict ion

by

Donald K. Cohen, Ph.D.

Gwidon W. Stachowiak and Andrew W. Batchelor (2005), Engineering Tribology, Elsevier Butterworth-Heinemann, UK

Bharat Bhushan, (2002), Introduction to Tribology, John Wiley & Sons, New York.

Duncan Dowson, (1998), History of Tribology, Bookcraft (Bath) Ltd. Great Britain.

Peter J. Blau Friction Science and Technology, 1996, Marcel Decker, Inc. New York, NY 10016

Kenneth C. Ludema, Friction, Wear and Lubrication, 1996, CRC Press, Boca Raton, FLA 33431

Ernest Rabinowicz, Friction and Wear of Materials, John Wiley & Sons, 1995, New York, NY

Frank Phillip Bowden and David Tabor (1982), Friction, An Introduction to Tribology, Robert E. Kreiger. Floriday, USA.

Key References:


2/44

2

Surface Texture - Basics

Surface: The boundary that separates an object from another object,

substance, or space

Texture: The composite of certain deviations that are typical

of the real surface. It includes roughness and waviness

X

YZ

Surface Roughness, Ra (2D), Sa (3D) is the average of the absolute

value of profile heights over a given length (area).

dxdyyxZA

S

LxLy

a =00

),(1

LR

LZ x dxa

L

= 1

0

( )

2D

3D

ASME B46.1 2009

X

Z


3/44

3

dxdyLyLx

yxZAq

S =0 0

2)),((1Sq: The Root-mean-square deviation of the

surface

X

YZ

Height Parameters

Ssk:Skewness of surface height distributiondxdy

LyLxyxZ

ASqskS =

0 0

3)),((3

1

Sku:Kurtosis of surface height distribution dxdyLyLx

yxZASqku

S =0 0

4)),((4

1

Sa: The average deviation of the surfacedxdy

LyLxyxZ

ASa =

0 0),(1

ASME B46.1 / ISO 25178-2

Ssk 0.0 Sku< 3.0 Sku> 3.0


4/44

4

What is Friction?

Friction is the resistance to motion during sliding or rolling that is

experienced when one solid body moves tangentially over another withwhich it is in contact. The resistive tangential force, which acts in a direction

directly opposite to the direction of motion is called the friction force

(Bhushan)

Ff= W is the coefficient of friction

Friction is NOT strictly a property of the material

its a system response

Sliding Friction and Surface Texture Introduction

F

Ff

W

F

Ff

W

Sliding Friction Rolling Friction


5/44

5

Friction Good or Bad?


Application Specific: Sometimes need friction

sometimes want it to be zero

www.animationfactory.com
http://www.animationfactory.com/en/search/close-up.mc?&oid=4953579&s=1&sc=1&st=7&q=friction&spage=1&hoid=886b7abc58e4bdfa271cb4080c9131bc


6/44

6

Sliding Friction and Surface Texture

Ernest Rabinowicz, Friction and Wear of Materials, John Wiley & Sons, 1995, New York, NY


7/44

7 Sliding Friction and Surface Texture Introduction

History

1452-1519

1. The areas in contact have no effect on friction.

2. If the load (weight) of an object is doubled, its friction will also be doubled

Leonardo da Vinci


8/44

8

No Picture Exists!! It is impossible that these irregularities shall not be partly convex and partly

concave, and when the former enter upon the latter they shall produce a certain

resistance when there is an attempt to move them.

Considered the fundamental cause of friction being

surface roughness

force required to lift interlocking asperities

1663-1705

Guillaume Amontons


History
http://images.google.com/imgres?imgurl=http://www.parkour.org.uk/images36/news/smiley_face.gif&imgrefurl=http://www.parkour.org.uk/parkour_old_news.html&h=75&w=75&sz=2&tbnid=teoFrWvC_VEJ:&tbnh=68&tbnw=68&start=10&prev=/images%3Fq%3Dsmiley%2Bface%2Bfrench%26hl%3Den%26lr%3Dlang_en%26safe%3Dactive


9/44

9Sliding Friction and Surface Texture Introduction - History

Does friction primarily comes from surface roughness..?

1683-1744

John Theophilus Desagulier

yet it is found by experience that the flat surface of metals or other

bodies may be so far polished as to increase the friction

Introduces the concept of cohesion (today we call it adhesion)

Trouble: Adhesion theory cant explain laws of

frictionApparent area


10/44

10 Sliding Friction and Surface Texture Introduction - History

1736-1806

Charles Augustin Coulomb

Coefficient of friction is independent of velocity

Considers Ff~ Adhesion + Roughness

Turned Surface Max Slope ~15o

Frank Phillip Bowden and David Tabor (1982), Friction An Introduction to Tribology,


11/44

11 Sliding Friction and Surface Texture Introduction - History

1. The apparent area of contact has no effect on friction.

2. If the load (weight) of an object is doubled, its friction will also be doubled

Refresh!!

So which is it? Roughness?, Adhesion?, Shearing of Asperities (Lesile, Phillipe de la

Hire)?

Ff= W


12/44

12Sliding Friction and Surface Texture Introduction - History

Frank Phillip Bowden(1903-1968)

Abbott and Firestone (1933) ( U of Michigan)-Invent Profilometer

David Tabor (1913-2005)

putting two solids together is rather like turning Switzerland upside

down and standing it on Austria their area of intimate contact will be

small (1950)

more closely Iowa on top of the Netherlands (Thomas 1973)


13/44

13Sliding Friction Strength of Materials Review

Bharat Bhushan, (2002), Introduction to Tribology, John Wiley & Sons, New York

Stress = Force/area

Strain L/LE Young's Modulus of Elasticity

Y - Yield Strength

H - Hardness Resistance of metal to plastic deformation, usually by indentation

H ~ 3Y (metals)


14/44

14Sliding Friction- Physics

Bowden/Tabor revisit adhesion theory....why?

Asperity slopes


15/44

15Sliding Friction - Physics

Bowden/Tabor key point

Arp

= W/H;

Real area of contact

1) Proportional to Force

2) Independent of apparent area of contact

sounds like friction!

Maybe friction will be related to the real area of contact??

Friction (Ff) is the force required to shear intermetallic junctions plus the force required to

plow the surface of the softer material by asperities of the harder surface

(Bowden/Tabor).Consider the shear term

Ffp = Arps (s is shear strength of junctions)

Recall (pure plastic):Arp= W/H so Ffp= W(s/H) =s/H

metals, s~0.5Y=H/6

So =1/6 (~0.2)


16/44

16Sliding Friction - Physics

Bowden/Tabor:

Ffpproportional to normal force

Ffp not dependent on the apparent area of contact

Ffpwill be reduced by lubricants that lower shear strength of asperities

Ffp(adhesion) not dependent on the surface roughness ???

BUT:

Are all contacts purely plastic?

How about elastic deformation?

Typically surface deforms plastically (work hardens?) then stabilizes-elastic support

Experience indicates some frictional dependence on surface roughness

Ff= W(s/H)
http://images.google.com/imgres?imgurl=http://www.sosnet.com/images/apc/Checkmark.jpg&imgrefurl=http://www.sosnet.com/apc.10.checklist.asp&h=194&w=200&sz=4&tbnid=K74tR5bxmyYJ:&tbnh=96&tbnw=99&hl=en&start=1&prev=/images%3Fq%3Dcheckmark%26hl%3Den%26lr%3Dlang_en%26safe%3Doff%26sa%3DGhttp://images.google.com/imgres?imgurl=http://www.sosnet.com/images/apc/Checkmark.jpg&imgrefurl=http://www.sosnet.com/apc.10.checklist.asp&h=194&w=200&sz=4&tbnid=K74tR5bxmyYJ:&tbnh=96&tbnw=99&hl=en&start=1&prev=/images%3Fq%3Dcheckmark%26hl%3Den%26lr%3Dlang_en%26safe%3Doff%26sa%3DGhttp://images.google.com/imgres?imgurl=http://www.sosnet.com/images/apc/Checkmark.jpg&imgrefurl=http://www.sosnet.com/apc.10.checklist.asp&h=194&w=200&sz=4&tbnid=K74tR5bxmyYJ:&tbnh=96&tbnw=99&hl=en&start=1&prev=/images%3Fq%3Dcheckmark%26hl%3Den%26lr%3Dlang_en%26safe%3Doff%26sa%3DGhttp://images.google.com/imgres?imgurl=http://www.sosnet.com/images/apc/Checkmark.jpg&imgrefurl=http://www.sosnet.com/apc.10.checklist.asp&h=194&w=200&sz=4&tbnid=K74tR5bxmyYJ:&tbnh=96&tbnw=99&hl=en&start=1&prev=/images%3Fq%3Dcheckmark%26hl%3Den%26lr%3Dlang_en%26safe%3Doff%26sa%3DG


17/44

17

Sliding Friction Strength of Materials Review again


Stress = Force/area- Strain L/LE Young's Modulus of Elasticity

Y - Yield Strength

H - Hardness Resistance of metal to plastic deformation, usually by indentation

H ~ 3Y (metals)

- Poissons ratio

= - trans/ longitudinal

= L/Lhttp://silver.neep.wisc.edu/~lakes/PoissonIntro.html


18/44

18

Sliding Friction Physics Real Contact Hertz

1880s

R1

R2

W

Elastic Real Area of Contact, Are

3/2

*

4

3

=

E

WRAre

21

111

RRR+=

2

2

2

1

2

1

*

111

EEE

+

=

1857-1894

Heinrich Hertz


19/44

19Sliding Friction Physics Real Contact

3/2

*4

3

=

E

WR

Are

In words

Smaller Asperity Radii Smaller real area

Larger Elastic Modulus Smaller real area

GPaEsteel 200

1 GPa = 1x 109

N/M2

= 1.45 x 105

psi

GPaElead 15

GPaESiC 500

GPaErubber 001.0


20/44


Greenwood & Williamson - 1966

W

Aa Apparent Area

Aa

W

Asperities of same radiiAsperities of random distribution of heights (e.g. Gaussian, exponential etc..)

Asperities separated no interaction

Exponential Distribution success!!

2/1

*

R

E

WAre

W - force applied

E*- composite Elastic Modulus

R summit radius of curvature

is the standard deviation of the peak heights


21/44


Greenwood Williamson - 1966

W

Aa

W

Recall:Ffe= Ares (s is shear strength of junctions)

Substituting for Are

Ffe~ W

Ffe has no dependence on Apparent Area

Consistent with Amonton

2/1

*

R

E

WsFfe

Aa

22
http://images.google.com/imgres?imgurl=http://www.sosnet.com/images/apc/Checkmark.jpg&imgrefurl=http://www.sosnet.com/apc.10.checklist.asp&h=194&w=200&sz=4&tbnid=K74tR5bxmyYJ:&tbnh=96&tbnw=99&hl=en&start=1&prev=/images%3Fq%3Dcheckmark%26hl%3Den%26lr%3Dlang_en%26safe%3Doff%26sa%3DGhttp://images.google.com/imgres?imgurl=http://www.sosnet.com/images/apc/Checkmark.jpg&imgrefurl=http://www.sosnet.com/apc.10.checklist.asp&h=194&w=200&sz=4&tbnid=K74tR5bxmyYJ:&tbnh=96&tbnw=99&hl=en&start=1&prev=/images%3Fq%3Dcheckmark%26hl%3Den%26lr%3Dlang_en%26safe%3Doff%26sa%3DG


22/44

22

2/1

*

R

EWAre

Dry Friction Physics Real Contact

Greenwood Williamson - 1966

In Words

Larger the applied force larger real area of contact (friction )

Larger Elastic Modulus smaller area of contact (friction)

Larger Summit Radii larger area of contact (friction)

Larger the roughness smaller area of contact (friction)*

Ffe= Ares

Friction ~ shear strength of the real regions of contact

* elastic domain

23


23/44


Greenwood Williamson 1966

1) Only Exponential law gives Laws of Friction results

2) Other frictional mechanisms (e.g. plowing) not considered

3) Asperity on asperity/ resolution - reality

4) Assumes elastic contact only next step is plasticity

Laws of friction follows since all surfaces have textureThe mean asperity real contact area is independent of applied force -Exp dist onlyRThe mean asperity real pressure very weak dependence on applied force -Exp dist onlyE*(/R)1/2The number of contacts are proportional to applied force -Exp Dist only W/(E*(3R)1/2)

Good News

Bad News

24


24/44

24Sliding Friction Physics Elastic and Plastic

Greenwood & Williamson 1966

2/1

*

R

EWAre Arp= W/H

Pure ElasticPure Plastic

Plastic deformation will begin when the pressure at the asperity is greater than H.

Calculate for various distribution (e.g. Exp) the probability of plastic deformation

...),( Wf

A

A

re

rp=

2

1*

=

RH

E Plasticity Index

(very weak dependence on W)

H- hardness of lowest hardness surface at interface

25


25/44

25

2

1*

=

RH

E

rA

2/1

*

R

E

WAre

Arp= W/H

1.00.6

Sliding Friction Physics Elastic and Plastic


1.0 plastic regime, lower Ar,but..deformation, wear etc. eventually back to elastic regime or

.scoring scuffing galling failure etc..

26


26/44

26

Sliding Friction Physics Elastic and Plastic


2

1*

=

RH

E

160 nm

R 10 um

100 nmR 70 um

Likely - Elastic Deformation Likely - Plastic Deformation

27


27/44

27Sliding Friction Physics Reset Real Area of Contact

2/1

*

R

E

WAre

Arp= W/H

Elastic Mode

Plastic Mode2

1*

= RH

E

Plasticity Index - Predicts Elastic or Plastic

Friction relates to the Adhesion between surfaces at the real area of contact.

Adhesion chemical bonds, mechanical, etctotally different/new field

Ffp = Arps (s is shear strength of junctions)

Recall (pure plastic):Arp= W/H so Ffp= W(s/H) ap=s/H

Ffe= Ares (s is shear strength of junctions)Recall (pure elastic):

2/1

*

R

E

WAre

sWE

RFfe

2/1

2*

2/1

2*

E

Rsae

28


28/44

28Dry Friction Physics Elastic and Plastic - Models

AF- Abbot Firestone 1933 Pure Plastic (Truncation Model)

GW Greenwood and Williamson 1966- Elastic only spherical contacts etc.

CEB Cheng, Etsion, Bogy 1987 Elastic/Plastic

KE Kogut and Etsion 2004 - Elastic/Plastic and tangential loading effects

Jamari and Schipper 2006 Elastic/Plastic Ellipsoids asperities

J. Jamari and D.J. Schipper, An elastic-plastic contact model of ellipsoid bodies, Tribology Letters, Vol. 21 No. 3 march 2006.

F=external Load

P=Aspertiy Contact Force

Fs=Total Adhesive Force

Qmax-Static Friction Force

29


29/44

29Friction Physics Rough Surface Contacts

C.Y. Poon and R. S. Sayles, The Classification of rough surface contacts in relation to tribology, J. Phys D: Appl.

Phys. 25 (1992) A249-A256

FrictionCoefficient

30 Sliding Friction Engine Val e Train Components


30/44

30

2

1

*

=

RH

E

rA

2/1

*

R

E

WAre

Arp= W/H

1.00.6Unworn

high friction - deformation

Worn- run-in

Minimal frictionVery worn

high friction larger Aradhesion

Sliding Friction -- Engine- Valve Train Components

31
http://images.google.com/imgres?imgurl=http://energyoneclutches.com/images/P/BB-21.jpg&imgrefurl=http://www.energyoneclutches.com/product.php%3Fproductid%3D23%26cat%3D3%26page%3D1&usg=__2jNB3rq5L-m0ZJOlJMLIyyyQ2nY=&h=256&w=500&sz=28&hl=en&start=50&sig2=SHSjDyTp8b0uOESaslV1hw&tbnid=xDxq6uORixbHUM:&tbnh=67&tbnw=130&ei=jqVeSeT1C4P8MqjF-JII&prev=/images%3Fq%3Dclutch%2Bfriction%2Bplate%26start%3D40%26gbv%3D2%26ndsp%3D20%26hl%3Den%26sa%3DN


31/44

31

Sliding Friction

Transmission Components

2/1

*

R

E

WAre

32
http://images.google.com/imgres?imgurl=http://energyoneclutches.com/images/P/BB-21.jpg&imgrefurl=http://www.energyoneclutches.com/product.php%3Fproductid%3D23%26cat%3D3%26page%3D1&usg=__2jNB3rq5L-m0ZJOlJMLIyyyQ2nY=&h=256&w=500&sz=28&hl=en&start=50&sig2=SHSjDyTp8b0uOESaslV1hw&tbnid=xDxq6uORixbHUM:&tbnh=67&tbnw=130&ei=jqVeSeT1C4P8MqjF-JII&prev=/images%3Fq%3Dclutch%2Bfriction%2Bplate%26start%3D40%26gbv%3D2%26ndsp%3D20%26hl%3Den%26sa%3DN


32/44

32

Sliding Friction Physics Plowing Term

)tan(2=d Assumes isotropic material

Gear Surface 6 degd0.06


100:1 Vertical Magnification

33


33/44

33


Plowing Term Not that big for typical machined surface textures

But! - debris and wear particlesanother story

Sand Particle (Ottawa 16) Slope ~ 30 degd0.36

Also --Sandpaper, brake pads etc

34


34/44

34

Sa: In spec

Sdq: Low

Sa: In spec

Sdq: High

Problem: Brake Rotor Sa inspec some work ..some have NVH issues

Solution: Quantify the surfaces Spec additional texture parameters qSolution: Identify cause of texture variation..(materials? tools? setup?)

Glenn R. Weier, Kelsey Hayes 1995


dydxy

yxZLy

x

yxZLx

ASdq

2),(

0

2),(

0

1

+

=

Sdq: Root-Mean Square Surface Slope

35 Sliding Friction Physics Surface Texture
http://images.google.com/imgres?imgurl=http://www.roverparts.com/images/jaguar/JLM1305_Brake_Rotor_Front.jpg&imgrefurl=http://www.roverparts.com/Model/Jaguar.cfm&h=234&w=250&sz=4&hl=en&start=3&tbnid=owVawqxl7BC6sM:&tbnh=104&tbnw=111&prev=/images%3Fq%3Dbrake%2Brotor%26ndsp%3D18%26svnum%3D10%26hl%3Den%26safe%3Doff%26sa%3DN


35/44

Sliding Friction Physics Surface Texture

Bottom Line What is the connection between Surface Texture and Friction?

1) Friction - adhesion at the real area of contact

2) Friction - the deformation of asperities

2) Friction - plowing of the harder asperities into the softer material

Other Texture Parameters can relate to the real area of contact/asperity slope

..this has been the source of confusion/speculation/empirical work

Surfaces are not a nice distribution of asperities of radius R

36


36/44

Kotwal, C.A. and Bhuhsan, B. (1996) Contact Analysis of Non-Gaussian Surface for

Minimum Static and Kinetic Friction and Wear Tribol. Trans. 39, 890-898elastic limit

Sliding Friction Physics Surface Texture Parameters

Ssk Sku

Sku=3.0 Ssk=0.0

Ssk 0.0Sku< 3.0 Sku> 3.0


37/44

38C li d B Fi i h d Th i Eff t Oil C ti


38/44

Cylinder Bore Finishes and Their Effect on Oil Consumption

Stephen H. Hill,

SAE, 2001-01-3550

LD=Production Gasoline Auto Engines

Units in um unless specified

CylinderBore

Best predictor of Oil Consumption, Vo,

Vo = Svk(100-Mr2)/200

Careful of Vo units etc.

39Sliding Friction Ph sics S rface Te t re Parameters


39/44

Sliding Friction Physics Surface Texture Parameters

Functional Bearing Area Parameters .. Spk, Sk, Svk....

40


40/44

K

S

SS

SS

SSSI

z

ask

smvk

pk

k +

=

1log

SI = Surface Index for TFM

SIW SI for Optical Profiler

SIT SI for Stylus ProfilerLargest SI Worst TFM

K for optical or stylus

Tribology Transactions, 51: 784-789, 2008

41Effect of Roughness Parameter and Grinding Angle on Coefficient of
http://images.google.com/imgres?imgurl=http://www.northernautoparts.com/Images/Uploaded/BRM_Flex_hone/After_Flex_Hone_A400pxl.jpg&imgrefurl=http://www.northernautoparts.com/ProductDetail.cfm%3FProductId%3D2645&usg=__jRgxakz-gE67QPzETdo6IdC4faY=&h=503&w=400&sz=82&hl=en&start=8&sig2=uY3lUyiHobe6OxG06psrJA&tbnid=F8M4_p6aJAyUqM:&tbnh=130&tbnw=103&ei=ojekScbbFpXlmQeMzsi0Bg&prev=/images%3Fq%3Dtorn%2Band%2Bfolded%2Bmetal%26gbv%3D2%26hl%3Den%26sa%3DG


41/44

Effect of Roughness Parameter and Grinding Angle on Coefficient of

Friction When Sliding os Al-Mg Alloy over EN8 SteelPradeep L. Menezes Kishore and Satish V. Kailas,

ASME Journal of Tribology, October 2006, Vol 128. p 697-704

Thecoefficient of friction and transfer layer formation were observed to dependprimarily on the direction of the grinding marks of the harder mating surface andindependent of the surface roughness of harder mating surface.

Direction of Motion

42 Modeling and Optimizing Honing Texture for Reduced Friction in Internal


42/44

Modeling and Optimizing Honing Texture for Reduced Friction in Internal

Combustion Engines

Jeffrey Jocsak, Yong Li, Tian Tain and Victor K. Wong

SAE, 2006-01-0647MIT-Ring-Pack Simulation Program

Reduce Cross Hatch Angle -reduces friction (less asperity contact/more hydrodynamic lift)

However, -Tradeoff- As reduce cross hatch angle increase risk of scuffing (TDC) / oil consumption

u

u

=

0=

h

Friction

43 Sliding Friction 3D Texture Directional Analysis


43/44

Cross Hatch Angle Analysis

Sliding Friction 3D Texture Directional Analysis

44

C l i Slidi F i i d S f T


44/44

Conclusion Sliding Friction and Surface Texture

Friction relates to adhesion of surfaces at points of real contact

.Real area of contact relates to surface texture

Friction relates to deformation / plowing asperity shape/slope

Asperity Shape/Slope relates to surface texture

The challenge is choosing the right lateral/height resolution

for measurement and the appropriate texture parameters torelate to friction and then to optimize for desired friction

What is clear, is that the study of surface roughness continues to get more

complicated and that we are a long way from understanding it.

J. A. Greenwood (1992)

I.L. Singer and H.M. Pollock (eds.) Fundamentals of Friction: Macroscopic and

Microscopic Processes 57-76 1992 Kluwer Academic Publishers, Netherlands.

bruker-slidingfriction-presentation-07262013.pdf

Documents