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1、ExperimentalInvestigationofBricksUnderUniaxialTensileTestingBSTRACTSofteningisagradualdecreaseofmechanicalresistanceresultingfromacontinuousincreaseofdeformationimposedonamaterialspecimenorstructure.Itisasalientfeatureofquasi-brittlematerialslikeclaybrick,mortar,ceramics,stoneorconcretew
2、hichfailduetoaprocessofprogressiveInternalcrackgrowth.Suchmechanicalbehaviouriscommonlyattributedtotheheterogeneityofthematerial,duetothepresenceofdifferentphasesandmaterialdefects,suchasflawsandvoids.Fortensilefailurethisphenomenonhasbeenwellidentifiedforconcretebutveryfewresultsexistsf
3、orclaybrick..Inthepresentpaper,theresultsofanextensivesetoftestscarriedoutatUniversityofMinhoandincludingthreedifferenttypesofbackunderniaxialtensionwillbepresented.Bothtensilestrengthandfractureenergyarequantified,withrecommendationsfortheadoptionofpracticalvalues.INTRODUCTIONThetensile
4、behaviourofconcreteandotherquasi-brittlematerialsthathaveadisorderedInternalstructure,suchasbrick.canbewelldescribedbythecohesivecrackmodelproposedinitiallybyHILLERBORG[1].Thismodelhasbeenwidelyusedasthefundamentalmodelthatdescribesthenon-linearfracturemechanicsofquasi-brittlematerials,e
5、.g.[2,3].Accordingtothismodelandduetocrackinglocalization,whichisacharacteristicoffractureprocessInquasi-brittlematerials,thetensilebehaviourIscharacterizedbytwoconstitutivelawsassociatedwithdifferentzonesofthematerialduringtheloadingprocess.seeFigure1.Theelastic-plasticstress-strainrela
6、tionshipofFigurelaisvaliduntilthepeakloadisreached.ItisnotedthatbeforethepeakInelasticbehaviouroccursduetomicro-crackingandtheenergydissipatedinthisprocessisusuallyneglectedforthecalculationofthefractureenergy.Thestress-crackopeningdisplacementrelationshipofFigurelbdescribesthestrainsoft
7、eningbehaviourinthefractureprocesszoneafterthepeak.Thecohesivestress-openingdisplacementdiagramIscharacterizedbythegradualdecreaseofstressfromftmaximumvalue,tozero,correspondingtotheIncreaseofthedistancebetweenthetwoedgesofthecrackfromzerotothecriticalopening,u,Thesofteni
