mae 493n 593t lec12
TRANSCRIPT
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TribologyinMechanicalEngineeringMAE493N/593T
Dr.Konstantinos
A.
Sierros
WestVirginiaUniversity
Mechanical&AerospaceEngineering
ESBAnnex
263
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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/Lubricantsurface.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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Wearmechanisms
Delaminationwear
Duringrunning
in
the
surfaces
in
contact
are
losing
material
in
order
to
conform
Onthewearmap,contactconditionsmovefromrighttoleft(lowersurfaceslope)
Slidingvelocityislowenoughsoitdoesnotcausefrictionalheating
Frictionalforcedeformsthesurfacelayer,shearingitintheslidingdirection
Lossof
material
in
the
form
of
thin
flakes
or
platelets
(Delamination
wear)
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Wearmechanisms
Delaminationwear
Suh
(1986)
did
alot
of
work
on
delamination
wear
Surfacetractionexertedbyharderasperitiesinducesplasticsheardeformationof
thesoftersurfacewhichaccumulateswithrepeatedloading
Assubsurfacedeformationcontinues,cracksareformingbelowthesurface
Thosecracks
initiate
from
pre
existing
flaws/defects
Cracknucleationverynearthesurfaceisnotfavoredbecauseoflargehighly
compressivestresses
Cracksareextendingandpropagatingandjoiningneighboringcracks
Wearsheets
are
lost
or
delaminate
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Wearmechanisms
Delaminationwear
Thicknessof
awear
sheet
depends
on
subsurface
crack
location
Depthistypicallyofthesameorderasthesizeofanasperity
Modelforthissituation
Assumeinitial
distribution
of
voids/inclusions
at
near
surface
of
volume
fraction
fv
Atfv delamination initiates
o isthenettotalplasticshearstrainaccumulatedperasperitypass
AnArchardwearlawcanbegeneratedandthedimensionlessKis
givenby;
*
A
vo
f
fK
=
Criticalareafraction
ofvoids
to
generate
awearparticle
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*
A
vo
f
fK
=
Wearmechanisms
Foragivenmaterialthefractionscanbeconsideredasconstants
sothatwearrate
dependsono
If0.3theflowfieldextendstothesurfaceandtheplasticstrainperpass(o
)
becomesmuchlarger Therefore
for
higher
friction,
wear
coefficient
can
rapidly
increase
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Delaminationwear
http://www.oilcheck.com.au/Tutorial/17_delamination_wear.htm
http://www.oilcheck.com.au/Tutorial/17_delamination_wear.htmhttp://www.oilcheck.com.au/Tutorial/17_delamination_wear.htm -
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http://www.oilcheck.com.au/Tutorial/17_delamination_wear.htm
Delaminationwear
http://www.oilcheck.com.au/Tutorial/17_delamination_wear.htmhttp://www.oilcheck.com.au/Tutorial/17_delamination_wear.htm -
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Wearmechanisms
Fatiguewearinrollingcontacts
Racesand
rolling
elements
are
made
of
high
strength
material
Normally,theloadingisentirelyelasticandthereislittleslipattheinterface
Operatingtemperaturesarelessthan200oC
Verylittleadhesive,abrasive,oxidativewear
Therefore,
many
millions
of
cycles
can
be
achieved
with
no
visible
degradation
of
thesurfaces
However,atsomepointaparticlewillspallawayfromoneofthesurfaces
Thenfurther
deterioration
will
follow
rapidly
Well
developed
Fatigue SpallsonBearingInnerRacehttp://www.machinerylubrication.com/Read/664/wearbearingsgearsTypicalSpallCrater
(ScaleBar=400m)
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Wearmechanisms
Fatiguewearinrollingcontacts
Theparticlesaremuchlargerthantheverysmallfragmentsassociatedwith
adhesiveorabrasivewear
This
characteristic
pitted
surface
is
related
to
the
general
phenomenon
of
fatigue Thereisnorollingloadbelowwhichthereisa100%chanceof
infinitebearinglife
Bearingliveslimitedbyfatiguearegenerallyviewedstatistically(Weibull)
TypicalSpallCrater
(ScaleBar=400m)
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Geartoothcontacts
Combinationof
rolling
and
sliding
conditions
Theycanalsodeveloppittedsurfacestypicalofsurfacefatigue
Thefourballtestcanbeusedfortestingmaterialsandlubricantsforsuch
situations
Wearmechanisms
http://www.machinerylubrication.com/Read/732/rollingbearingscontamination
R.Martins,N.Cardoso,J.Seabra,(2008)"Influenceoflubricanttypeingear
scuffing",IndustrialLubricationandTribology,Vol.60Is:6,pp.299
308
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Wearmechanisms
Frettingand
corrosion
wear
Frettingwearoccursbetweentwosurfacesthathavearelativeoscillatorymotion
ofsmallamplitude(afewtensofm)
FormaterialscontainingFe,frettingresultsinreddishbrowndebris
It
is
powder
made
up
of
iron
oxide
particles
and
acts
as
grinding
paste
leading
to
highlypolishedpatches
Atypicalpatternisfollowed;
Mechanicalaction
disrupts
oxide
film
Freshmetalsurfaceisexposed
Freshmetalsurfaceisthenoxidizinginatmosphere
Particlesofthedisruptedfilmaretrappedinthecontactandareabradingthe
surface(abrasion
wear
element)
Areasofsurfacesthatareincompletelyoxidizedcanadhere(adhesivewear
element)
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Wearmechanisms
Schematicrepresentation
of
fretting
wear
http://www.timroninc.com/teknote_Mar2007.html
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Wearmechanisms
Frettingandcorrosionwear
Examplesinwhichfrettingisaproblem
Staticjoints(flanges,couplings,keywaysetc)
Undersides
of
screw/bolt
heads
Changesinsurfaceconditionbyplating,coatingorchemicaltreatmentscanbe
utilizedtoreducefrettingwear
In
the
case
of
aluminium
and
its
alloys,
ablack
powder
is
produced
(mixture
of
aluminiumandalumina)
Frettinghasalsobeenobservedwithalloysbasedonnickel,cobaltand
molybdenum
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Wearmechanisms
Erosivewear
Erosivewearistheprocessofmaterialremovalbytheimpingementofparticles(at
highvelocity)oncomponentsurfaces
Erosionisdeliberatewhencleaningbyironshotofsandparticles
However,erosion
problems
have
been
observed
in:
Transportofpowdersandslurries
Impactofdustonbladesofturbomachinery
Operationoffluidbedcombusters
Erosion
particles
do
not
have
to
be
solid
(water
droplets
can
be
an
alternative)
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Erosivewearinsteampipe
Wearmechanisms
Erosion particles do not have to be solid (water droplets can be
an alternative)
(eg in wet steam)
http://www.aludra.nl/Eng/Coatings/Weerstand%20tegen%20slijtage/Erosive/erosive.htm -
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Wearmechanisms
Erosivewear
Erosionisquantifiedusingthespecificweightloss
Specific
weight
loss:
Loss
of
mass
from
the
surface
in
question
resulting
from
aunit
massoftheimpingingparticles
ErosiontestinginvolvesblastingastreamofabrasiveparticlesatvelocityV
against
atargetspecimen
nVtcons = tan
2
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Wearmechanisms
Erosivewear
Thebehaviourofanindividualerosionparticlemustbestudied
Experimentally,agasgunisusedtofireasingle
particleonasurface
Highspeedphotographyisusedtocapturethedetails
Animportant
parameter
is
the
angle
of
impact
Wear mechanisms
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WearmechanismsErosivewear
Forductilemetalscurve(a)
At
20
o
erosionis
maximum
Frontfaceoftheparticleexhibitsalargeattackangle(similartoabrasion)
Photographyconfirmsclearsimilaritiesbetweenerosionandabrasion
Deformationcausedbyanangularparticledependsalsoonitsorientationwhenit
strikesthe
surface
Circularparticlesvs
angularparticles
Brittlematerials(curveb)
Materialisremovedfromsurfacebytheformationandintersectionofcracks
h i
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WearmechanismsErosivewear Brittlematerials(curveb)
Materialisremovedfromsurfacebytheformationandintersectionofcracks
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Summary
Mechanical wear processes
Fatigue wear in rolling contacts
Fretting and corrosion wear
Erosive wear