8/8/2019 Mae 493n 593t Lec9
1/21
TribologyinMechanicalEngineeringMAE493N/593T
Dr.Konstantinos
A.
Sierros
WestVirginiaUniversity
Mechanical&AerospaceEngineering
ESBAnnex
263
8/8/2019 Mae 493n 593t Lec9
2/21
Project
listTeams:Names&Members
Projecttitle
8/8/2019 Mae 493n 593t Lec9
3/21
Wearofcoins
Eachgroupmustsubmit1shortreport(2pagesmaxincluding
figures,graphs,tablesetc)
Deadline:Thursday
7October
2010
(during
class)
Pleasetypeyourreportandsubmitahardcopy
8/8/2019 Mae 493n 593t Lec9
4/21
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.shtml8/8/2019 Mae 493n 593t Lec9
5/21
Definitionofwear
Wearistheprogressivedamage,involvingmaterialloss,whichoccuronasurface
movingrelativelytoanothersurface
Wearistheinevitablecompanionoffriction
Lubricantsareemployedinordertoreducefrictionandwear
Wearratew(forrolling/slidingcontact):Thevolumelostfromthewearingsurface
perunitslidingdistance
Wearratedependson;
1.Normalload
2.Slidingspeed
3.Temperature4. Thermalpropertiesofinvolvedsurfaces
5.Mechanicalpropertiesofinvolvedsurfaces
6.Chemicalpropertiesofinvolvedsurfaces
8/8/2019 Mae 493n 593t Lec9
6/21
Weartesting
Slidingwear
A.Ringonring
B.Facetoface
C.Pinon
disc
D.Pinonrim
E.Blockonring
F.Pinonflat
(FromI.Hutchings Tribology)
8/8/2019 Mae 493n 593t Lec9
7/21
Contactconditions
(FromI.Hutchings
Tribology)
8/8/2019 Mae 493n 593t Lec9
8/21
Classificationofwear:Wearmaps
Wearcanbemild
orsevere
Thisis
not
based
on
any
value
of
wear
rate
but
on
observation
Increasedloading,slidingspeed,bulktemperatureleadstoincreasedwearrate
8/8/2019 Mae 493n 593t Lec9
9/21
Classificationofwear:Wearmaps
Wearcanbecausedby;
Abrasion
Adhesion
Oxidation
Delamination
Melting
Corrosion
andotherphenomena
H
W
Kw=
Archard
wearequation
Wearrate
Wearcoefficient
Surfacehardnessof
wearingmaterial
Appliedload wisdirectlyproportionaltoW
wisinverselyproportionaltoH
8/8/2019 Mae 493n 593t Lec9
10/21
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
8/8/2019 Mae 493n 593t Lec9
11/21
Leadedbrassagainststeel
Subsurfacedeformation
(FromI.Hutchings
Tribology)
8/8/2019 Mae 493n 593t Lec9
12/21
Testingwasdoneusingslowslidingandlowsurfacepressures
i.e.modest
temperature
increase
Kcanchangeifconditionsbecomemoreseverebecauseoftransitionsof
wearmechanisms
Kisalwayslessthan1
0.18
8/8/2019 Mae 493n 593t Lec9
13/21
Wearandfriction
There
is
no
simple
correlation
between
friction
and
wear
Qualitativelywemightexpecthigherfrictionalforcestoinvolverelativelyhigh
wear
Somematerialcombinationscanproduceverysimilarfrictionalforcesbut
very
differentwear
8/8/2019 Mae 493n 593t Lec9
14/21
Wearmaps
Wearmapsareusedtoexplorepatternsofwearbehaviourunderchangingconditions(Temperature,slidingspeed,loadetc) Wearmapsarespecifictoaparticularmaterial
Wearmapsalsoincorporateregimesofdifferentsurfacechemicalreactions
associatedwith
temperature
effects
Nodetailonmechanicalformsofwear
Wearmapscanbeconstructedfromexperimentaldata
Wearmapscanalsobebuiltfrommodelbasedequations
8/8/2019 Mae 493n 593t Lec9
15/21
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
8/8/2019 Mae 493n 593t Lec9
16/21
Wearmaps
Appliednormalpressurevssliding
speed
Differentwearmechanismsare
traversedby
contours
of
equal
normalizedwearrate
LinePQdividesgraphintworegions
LHSregion:weariscontrolledby
mechanicalprocesses
(wear
rate
dependsonloadbutnotgreatlyon
speed)
RHS
region:Thermochemicaleffects
dominate(wearratedependsonboth
Loadandspeed)
W
8/8/2019 Mae 493n 593t Lec9
17/21
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
8/8/2019 Mae 493n 593t Lec9
18/21
Wearmaps alternativepresentation
h/ vs.
Thistypeofwearmapgivesmoreemphasistothemechanicalaspectsofwearandlessto
thermalsincevelocityisnotanindependentvariable
Shearstrength
of
interface
Shearstrengthofweakermaterial
Surfaceroughness
parameter
Wear maps alternati e presentation
8/8/2019 Mae 493n 593t Lec9
19/21
Wearmaps alternativepresentation
axisiscalibratedlogarithmicallyinordertoincludetheelasticregime
Wecancalibratethexaxisusingtheplasticityindex whichindicatesgraduallyelasticto
plastic
transition
Atsteepervaluesofsurfaceslope(higher)thereisplasticdeformationoftheworn
surface
Contoursofequalwearratetraversethemap
Wear maps alternative presentation
8/8/2019 Mae 493n 593t Lec9
20/21
Wearmaps alternativepresentation
Whensurfacesaresmooth(
issmall)elasticdeformationscannotbeneglected
Theycansolelyaccommodatetheappliedloadsandwearisdependsonfatigueor
damageaccumulation
When1,
elastic
plastic
boundary
is
met
For>1substrateplasticdeformationbecomessignificantandwearis
delaminationwearduetoelastoplasticeffects
IFsurfaceisrough,abrasionwearisinitiated(thisinvolvessevereplastic
deformationploughing
&
micromachining)
Duringmicromachiningwearrateisloweredbecauseshearstressesarereduced
8/8/2019 Mae 493n 593t Lec9
21/21
Summary
Definitionofwear
Measurementofwear wear rate
Wearmaps
Recommended