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1、TerminologyforMechanicalPropertiesStress-Forceorloadperunitareaofcross-sectionoverwhichtheforceorloadisacting.Strain-Elongationchangeindimensionperunitlength.Young’smodulus-Theslopeofthelinearpartofthestress-straincurveintheelasticregion,sameasmodulusof
2、elasticity.Shearmodulus(G)-Theslopeofthelinearpartoftheshearstress-shearstraincurve.•Tensilestress,s:•Shearstress,t:Stresshasunits:N/m2orlb/in2ENGINEERINGSTRESS•Elasticmodulus,E•E~curvatureatroEislargerifEoislarger.PROPERTIESFROMBONDING:E•ElasticShearmo
3、dulus,G:t=Gg•ElasticBulkmodulus,K:•Specialrelationsforisotropicmaterials:simpletorsiontestpressuretest:Init.vol=Vo.Volchg.=DVOTHERELASTICPROPERTIES•Tensilestrain:•Lateralstrain:•Shearstrain:qStrainisalwaysdimensionless.(L)(-LL)ENGINEERINGSTRAIN(c)2003
4、Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.3(a)Tensile,compressive,shearandbendingstresses.(b)IllustrationshowinghowYoung’smodulusisdefinedforelasticmaterial.(c)Fornonlinearmaterials,weusetheslo
5、peofatangentasavariablequantitythatreplacestheYoung’smodulusconstantTheTensileTest:UseoftheStress-StrainDiagramLoad-Theforceappliedtoamaterialduringtesting.StraingageorExtensometer-Adeviceusedformeasuringchangeinlengthandhencestrain.Glasstemperature(Tg)
6、-Atemperaturebelowwhichanotherwiseductilematerialbehavesasifitisbrittle.Engineeringstress-Theappliedload,orforce,dividedbytheoriginalcross-sectionalareaofthematerial.Engineeringstrain-Theamountthatamaterialdeformsperunitlengthinatensiletest.(c)2003Brook
7、s/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.7Aunidirectionalforceisappliedtoaspecimeninthetensiletestbymeansofthemoveablecrosshead.Thecross-headmovementcanbeperformedusingscrewsorahydraulicmechanism(c
8、)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.9Tensilestress-straincurvesfordifferentmaterials.Notethatthesearequalitative•Ductilefractureisdesirableforstructuralapplic
