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1、CESSION15W55JWD刃他W^THefundamentalconceptsofstressandstraincan6eiCCustrated6yconsideringaprismatic6arthatisCoa(fe(f6ycLia[forcesTattheends,assHowninTig.1-1.人prismatic6arisastraightstructuralmem6erHavingconstantcrosssectiontHrougHoutitsCengtH.Inthisillustration,tfiea^iaCfo
2、rcesproduceauniformstretchingofthe6ar,hence,the6arissai(ftobeintension.Toinvestigatethe——/TinternalstressesprocfucedintHe6ar6ytfieaj(ia[:“forces,wema^eanffimaginarycutatsectionmmn^ig.l-la).Thisn1sectionista^enb>perpendicutartothe卜谄・】・1Bhsnwticbarintension[ongitudinaCcuqso
3、ftfie6ar;hence,itis^nownasacrosssection.14^nowisoCatethepartoftfiebartotherightofthecutasafreebody^ig.l-lb).ThetensiCeCoadTactsattherigHtendoftHefree6ody;attheotherendareforcesrepresentingtheactionoftheremovepartofthebaruponthepartthatremains,n^heseforcesCESSION15W55JWD刃他
4、W^THefundamentalconceptsofstressandstraincan6eiCCustrated6yconsideringaprismatic6arthatisCoa(fe(f6ycLia[forcesTattheends,assHowninTig.1-1.人prismatic6arisastraightstructuralmem6erHavingconstantcrosssectiontHrougHoutitsCengtH.Inthisillustration,tfiea^iaCforcesproduceaunifo
5、rmstretchingofthe6ar,hence,the6arissai(ftobeintension.Toinvestigatethe——/TinternalstressesprocfucedintHe6ar6ytfieaj(ia[:“forces,wema^eanffimaginarycutatsectionmmn^ig.l-la).Thisn1sectionista^enb>perpendicutartothe卜谄・】・1Bhsnwticbarintension[ongitudinaCcuqsoftfie6ar;hence,it
6、is^nownasacrosssection.14^nowisoCatethepartoftfiebartotherightofthecutasafreebody^ig.l-lb).ThetensiCeCoadTactsattherigHtendoftHefree6ody;attheotherendareforcesrepresentingtheactionoftheremovepartofthebaruponthepartthatremains,n^heseforcesarecontinuouslydistributecfoverthe
7、crosssection,analogoustotfiedistributionofhydrostaticpressureoverasubmergehorizontalsurface.加£intensityoffi)rce(tHatis,theforceperunitarea)iscaCCedthestressandiscommonlydenote(f6ytheQree^Cettero(sigma).AssumingthatthestressHasauniformdistributionovertfiecrosssedion(seeTig
8、.l-lb^wecanreadilyseethatitsresultantisequaltotheintensityatimesthecross-sectionalarea人ofthebar.
