Stress distributions in plasma-sprayed thermal barrier coati(4)

Stress distributions in plasma-sprayed thermal barrier coatings as a function of interface roughness and oxide scale thickness

30M.Ahrensetal./SurfaceandCoatingsTechnology161(2002)

26–35

Fig.4.FEresultsofthelocaldependencesoftheradialstressabovethepeakfordifferentamplitudes,A,andperiodlengths,L.Left:fixedL,amplitudes:1–30mm;right:fixedA,periodlengths:40–250mm.

Fig.5.FEresultsofthelocaldependencesofthenormalisedradialstressabovethepeakincombinationwiththeanalyticalfits(dashedlines)basedonEq.(3).Left:differentamplitudes(5–30mm,fixedL);right:differentperiodlengths(40–250mm,fixedA).Table1

RiforfittingthelocaldependencesoftheradialstressshowninFig.5A(mm)3020105202020202020

L(mm)656565652502001501006540

Ri(mm)6.77.69.612.446.035.024.414.27.64.0

decreaserelativelyfastintheTBC.Incontrast,inter-mediatevaluesofcurvaturehaveamorepronouncedsphereofinfluenceconcerningstressevaluationinthetopcoat.

3.1.2.2.Valley.Fig.6showsthecalculatedlocaldepend-encesoftheradialstressabovethebottomofthevalleyfordifferentAandLwiththeoriginoftheradialco-ordinateatthepoint‘V’inFig.1.Notethatsomedistanceawayfromtheinterfaceroughnessthecom-pressiveradialstressresultingfromthenegativecurva-tureofthevalleyconvergesintothe‘undisturbed’tensileradialstresswithinthetopcoat.

Besidesthisstressconversion,thedependencesdifferfromthoseobtainedforthepeaklocation.OveracertainrangemeasuredfromthebottomofthevalleythedecreaseofthestresslevelisslowerinthecaseofsmallvaluesofL.ThisisincontrasttothebehaviourfoundforthepeaklocationwherethedecreaseofsrishigherforsmallerL.ForR)2AtheradialstressesshowafasterdecreaseforsmallLsimilartothepeakcase.ConsideringthedependencesfordifferentamplitudesofA,wefindmoreslowlydecreasingstresslevelsin

plotitcanbeclearlyseenthattheanalyticalfitsfailfordistanceslargerthan25mm.

ConsideringthefitsbasedonEq.(3),highercurva-tures(largeA,smallL)correspondtosmallerparametersRi.ThusRiplaystheroleofaneffectiveattenuationlengthofthestresslevel.ThedifferentvaluesofRiusedforthefitsinFig.5arelistedinTable1.Thebasicresultisthatthehighradialstressesofverysharppeaks