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1、EFFECTSOFPORE/GRAIN-SIZEINTERACTIONANDPOROSITYONTHEFRACTUREOFELECTROCERAMICSChunshengLu,RobertDanzer,andFranzDieterFischer*ABSTRACTThestrengthofbrittlematerialsdecreasesasthesizeofspecimensincreases,andthisso-calledsizeeffectcanbedescribedbytheWeibullstatisticalfracturetheory.Recentexperimentsonth
2、efracturestrengthofelectroceramics,however,haveshownthatitisnotalwaysso.Electroceramics,suchaszincoxide(ZnO)appliedforvaristors,aremainlydesignedwithrespecttoelectricalratherthanmechanicalproperties,andthustheyusuallycontainahighdegreeofporositywhichmayactastheoriginoffracture.Itissuspectedthatthe
3、complexnatureofdefect-microstructureinteractionandthehighdensityofporosityarepossiblereasonsforthisinsensitivitytostrengthscaling.Inordertoverifythishypothesis,moregenerally,todeliberatethescalingbehaviorofthefracturestrengthofelectroceramicscontaininghighdensitiesofflaws,theeffectsofpore/grain-si
4、zeinteractionandporosityonthefracturestrengthinZnOceramicsareinvestigatedbasedonthefiniteelementanalysis.Thenumericalresultsshowthatthefracturestrengthismoreinfluencedbythepore/grain-sizeinteractionthanonlybythesizeofaporeoritsshapealthoughthestresssingularityofsharp*ChunshengLu,Institutfu¨rStrukt
5、ur-undFunktionskeramik,Montanuniversita¨tLeoben,A-8700Leoben,Austria;andLNM,InstituteofMechanics,AcademiaSinica,Beijing100080,China.RobertDanzer,Institutfu¨rStruktur-undFunktionskeramik,Montanuniversita¨tLeoben,A-8700Leoben,Austria.FranzDieterFischer,Institutfu¨rMechanik,Montanuniversita¨tLeoben,A
6、-8700Leoben,Austria.411412ChunshengLuetal.groovesaroundaporeiscloselyrelatedtotheirangles.Asaconsequencethepore/grain-sizeinteractionwillincreasethefractureprobabilityofsmallpores,andleadtoahomogenizationofcriticalflawsizes.Furthermore,thefiniteelementanalysisexhibitsthatthehighdegreeofporosity,es
7、peciallytheheterogeneousdistributionandtheclusteringofpores,couldbeconducivetofurtherhomogenizationofcriticalcracksizes.ThisimpliesthatthefracturestrengthofZnOceramicsisinsensitivetothesizeofspecimens,whichhasbee
