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TribologyinMechanicalEngineeringMAE493N/593T

Dr.Konstantinos

A.

Sierros

WestVirginiaUniversity

Mechanical&AerospaceEngineering

ESBAnnex

263

kostas.sierros@mail.wvu.edu

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Project

listTeams:Names&Members

Projecttitle

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Wearofcoins

Eachgroupmustsubmit1shortreport(2pagesmaxincluding

figures,graphs,tablesetc)

Deadline:Thursday

7October

2010

(during

class)

Pleasetypeyourreportandsubmitahardcopy

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Wear

IntroductionDefinitionandmeasurementofwear

Classificationofwear

Mechanismsofwear

Seizure

Meltwear

Oxidationdominatedwear

Mechanicalwearprocesses

Fatigue

wear

in

rolling

contacts

Frettingandcorrosionwear

Erosivewear

Thirdbodiesandwear

Wear

by

abrasive

contaminants

Interfacialthird

bodies

Debrisanalysis

Furtherreading

http://www.engineering.leeds.ac.uk/ietsi/Research_Projects/Lubricant

surface.shtml

DLCcoatingweartrackinoillubricatedconditions

http://www.engineering.leeds.ac.uk/ietsi/Research_Projects/Lubricant-surface.shtmlhttp://www.engineering.leeds.ac.uk/ietsi/Research_Projects/Lubricant-surface.shtmlhttp://www.engineering.leeds.ac.uk/ietsi/Research_Projects/Lubricant-surface.shtmlhttp://www.engineering.leeds.ac.uk/ietsi/Research_Projects/Lubricant-surface.shtml

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Definitionofwear

Wearistheprogressivedamage,involvingmaterialloss,whichoccuronasurface

movingrelativelytoanothersurface

Wearistheinevitablecompanionoffriction

Lubricantsareemployedinordertoreducefrictionandwear

Wearratew(forrolling/slidingcontact):Thevolumelostfromthewearingsurface

perunitslidingdistance

Wearratedependson;

1.Normalload

2.Slidingspeed

3.Temperature4. Thermalpropertiesofinvolvedsurfaces

5.Mechanicalpropertiesofinvolvedsurfaces

6.Chemicalpropertiesofinvolvedsurfaces

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Weartesting

Slidingwear

A.Ringonring

B.Facetoface

C.Pinon

disc

D.Pinonrim

E.Blockonring

F.Pinonflat

(FromI.Hutchings Tribology)

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Contactconditions

(FromI.Hutchings

Tribology)

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Classificationofwear:Wearmaps

Wearcanbemild

orsevere

Thisis

not

based

on

any

value

of

wear

rate

but

on

observation

Increasedloading,slidingspeed,bulktemperatureleadstoincreasedwearrate

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Classificationofwear:Wearmaps

Wearcanbecausedby;

Abrasion

Adhesion

Oxidation

Delamination

Melting

Corrosion

andotherphenomena

H

W

Kw=

Archard

wearequation

Wearrate

Wearcoefficient

Surfacehardnessof

wearingmaterial

Appliedload wisdirectlyproportionaltoW

wisinverselyproportionaltoH

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Classificationofwear:Wearmaps

Atlowloads,wearincreaseswithload

(inagreement

with

Archard equation)

H

WKw =

Leadedbrasspinslidingagainst

ahardstellite

ring

Ataloadbetween510Nasharp

increaseinwearisobserved

Beyond

10N

load,

wear

rate

is

in

agreementwithArchard

equation

again

Mildtosevere

Transition

&

Drop

in

resistance

Cobaltchromiumalloys

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Leadedbrassagainststeel

Subsurfacedeformation

(FromI.Hutchings

Tribology)

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Testingwasdoneusingslowslidingandlowsurfacepressures

i.e.modest

temperature

increase

Kcanchangeifconditionsbecomemoreseverebecauseoftransitionsof

wearmechanisms

Kisalwayslessthan1

0.18

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Wearandfriction

There

is

no

simple

correlation

between

friction

and

wear

Qualitativelywemightexpecthigherfrictionalforcestoinvolverelativelyhigh

wear

Somematerialcombinationscanproduceverysimilarfrictionalforcesbut

very

differentwear

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Wearmaps

Wearmapsareusedtoexplorepatternsofwearbehaviourunderchangingconditions(Temperature,slidingspeed,loadetc) Wearmapsarespecifictoaparticularmaterial

Wearmapsalsoincorporateregimesofdifferentsurfacechemicalreactions

associatedwith

temperature

effects

Nodetailonmechanicalformsofwear

Wearmapscanbeconstructedfromexperimentaldata

Wearmapscanalsobebuiltfrommodelbasedequations

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Wearmaps

nomA

k

UU =~Normalized

velocity

Sliding

speed

Thermaldiffusivity

Ofwearingmaterial

Nominalcontact

area

Hpp =~

Normalizedpressure

Normal

pressureHardness

pK

A

ww

nom

~~==

Normalized

wearrate

Wearrate

Wearcoefficient

Plot

against

eachother

W

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Wearmaps

Appliednormalpressurevssliding

speed

Differentwearmechanismsare

traversedby

contours

of

equal

normalizedwearrate

LinePQdividesgraphintworegions

LHSregion:weariscontrolledby

mechanicalprocesses

(wear

rate

dependsonloadbutnotgreatlyon

speed)

RHS

region:Thermochemicaleffects

dominate(wearratedependsonboth

Loadandspeed)

W

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Wearmaps

Mildtosevereweartransition

occurswhencontoursbecomesteep

(eg

arrowA)

A

small

change

in

speed

can

move

theoperatingpointfromonecontour

toanother

Aroundvalleys

ofcontoursfirst

wear

rate

increases

and

then

decreases(normalforsomematerials

suchassteels!!)

W lt ti t ti

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Wearmaps alternativepresentation

h/ vs.

Thistypeofwearmapgivesmoreemphasistothemechanicalaspectsofwearandlessto

thermalsincevelocityisnotanindependentvariable

Shearstrength

of

interface

Shearstrengthofweakermaterial

Surfaceroughness

parameter

Wear maps alternati e presentation

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Wearmaps alternativepresentation

axisiscalibratedlogarithmicallyinordertoincludetheelasticregime

Wecancalibratethexaxisusingtheplasticityindex whichindicatesgraduallyelasticto

plastic

transition

Atsteepervaluesofsurfaceslope(higher)thereisplasticdeformationoftheworn

surface

Contoursofequalwearratetraversethemap

Wear maps alternative presentation

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Wearmaps alternativepresentation

Whensurfacesaresmooth(

issmall)elasticdeformationscannotbeneglected

Theycansolelyaccommodatetheappliedloadsandwearisdependsonfatigueor

damageaccumulation

When1,

elastic

plastic

boundary

is

met

For>1substrateplasticdeformationbecomessignificantandwearis

delaminationwearduetoelastoplasticeffects

IFsurfaceisrough,abrasionwearisinitiated(thisinvolvessevereplastic

deformationploughing

&

micromachining)

Duringmicromachiningwearrateisloweredbecauseshearstressesarereduced

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Summary

Definitionofwear

Measurementofwear wear rate

Wearmaps